Chapter 38 - Angiosperm Reproduction and Biotechnology
1. Plant and angiosperm life cycles are characterized by an alternation of generations. Haploid (n) and diploid (2n) generations take turns producing each other. Through meiosis, the diploid sporophyte, produces haploid spores, which divide by mitosis, giving rise to multicellular male and female haploid plants—the gametophytes. The gametophytes produce gametes—sperm and eggs. Fertilization results in diploid zygotes, which divide by mitosis to form new sporophytes.
In angiosperms, the dominant generation is the conspicuous sporophyte plant, which produces the flower. Flowers are specialized shoots that function as unique reproductive structures bearing the reproductive organs of the angiosperm sporophyte. Male and female gametophytes develop within the anthers and ovules, respectively, of a sporophyte flower. Gametophytes became reduced in seed plants over the course of time, and evolved to become dependent upon their sporophyte parents. Consisting of only a few cells, angiosperm gametophytes are the most reduced of all plants. A male gametophyte (pollen grain) is brought to a female gametophyte (contained in an ovule embedded in the ovary of a flower) through pollination by wind, water, or animals. A union of gametes (fertilization) takes place inside the ovary. Ovules develop into seeds, while the ovary itself develops into the fruit around the seed.
2. Floral parts in order from outside in: sepals, petals, stamen, carpels
3. Sepals, petals, stamens, and carpels are all floral organs. They attach to the stem at the receptacle.
Sepals enclose/protect the floral bud before it opens. They are generally green and more leaflike in appearance than the other floral organs. Petals are brightly colored organs that attract insects/pollinators. Sepals and petals are sterile. Stamens are male reproductive organs that consist of a stalk (filament) and a terminal anther containing chambers called pollen sacs, which produce pollen. Carpels are the female reproductive organs of a flower. Flowers can have more than one carpel. At the base of a carpel is an ovary, inside of which one or more ovules can be found. Carpels also have a slender neck called the style. A sticky structure called the stigma exists are the top of the style, and serves as a landing platform for pollen. The anthers and the ovules bear sporangia, where spores are produced by meiosis and gametophytes later develop. The male gametophytes are sperm-producing structures called pollen grains, which form within the pollen sacs of anthers. The female gametophytes are egg-producing structures called embryo sacs, which form within the ovules in ovaries.
5. Complete flowers have all four organs and has both male and female reproductive organs), while incomplete flowers lack one or more of the four floral parts.
A bisexual flower is equipped with both stamens and carpels. All complete and many incomplete flowers are bisexual. A unisexual flower is missing either stamens (making it a carpellate flower) or carpels (making it a staminate flower).
A monoecious plant has staminate and carpellate flowers at separate locations on the same individual plant. For example, maize and other corn varieties have ears derived from clusters of carpellate flowers, while the tassels consist of staminate flowers. Meanwhile, dioecious species have staminate flowers and carpellate flowers on separate plants. For example, date palms have carpellate individuals that produce dates and staminate individuals that produce pollen.
6. Gametes are produced in the haploid generation by gametophytes. Male and female gametophytes develop within the anthers and ovules, respectively, of a sporophyte flower. They are produced by the process of mitosis.
7. Male gametophytes= pollen grains & female gametophytes= embryo sacs
8. The female gametophytes are egg-producing structures called embryo sacs, which form within the ovules in ovaries. One cell in the sporangium of each ovule, the megasporocyte, grows and then goes through meiosis, producing four haploid megaspores. In many angiosperms, only one megaspore survives. This megaspore divides by mitosis three times without cytokinesis, forming in one cell with eight haploid nuclei. Membranes partition this mass into a multicellular female gametophyte—the embryo sac. Three cells sit at one end of the embryo sac: two synergid cells flanking the egg cell. The synergids function in the attraction and guidance of the pollen tube. At the other end of the egg sac are three antipodal cells of unknown function. The other two nuclei, the polar nuclei, share the cytoplasm of the large central cell of the embryo sac.
9. Pollination, which brings male and female gametophytes together, is the first step in the chain of events that leads to fertilization. Some plants, such as grasses and many trees, release large quantities of pollen on the wind to compensate for the randomness of this dispersal mechanism. Some aquatic plants rely on water to disperse pollen. Most angiosperms interact with insects or other animals that transfer pollen directly between flowers.
10. Pollination by wind, water, or animals brings a male gametophyte (pollen grain) to a female gametophyte contained in an ovule embedded in the ovary of a flower. Fertilization is the union of the gametes.
11. The various barriers that prevent self-fertilization contribute to genetic variety by ensuring that sperm and eggs come from different parents. Dioecious plants cannot self-fertilize because they are unisexual. In plants with bisexual flowers, a variety of mechanisms may prevent self-fertilization. For example, in some species stamens and carpels mature at different times. Alternatively, they may be arranged in such a way that it is mechanically unlikely that an animal pollinator could transfer pollen from the anthers to the stigma of the same flower. The most common anti-self fertilizing mechanism is self-incompatibility, the ability of a plant to reject its own pollen and that of closely related individuals. If a pollen grain from an anther happens to land on a stigma of a flower on the same plant, a biochemical block prevents the pollen from completing its development and fertilizing an egg.
12. Double fertilization gives rise to the zygote and endosperm. The process begins after a pollen grain lands on a plant’s stigma. The grain absorbs moisture and then germinates, producing a pollen tube that extends down the style toward the ovary. The tip of the pollen tube enters the ovary directed by a chemical attractant (possibly calcium), and probes through the micropyle (a gap in the integuments of the ovule). The germinated pollen grain contains the mature male gametophyte. The nucleus of the generative cell divides by mitosis to produce 2 sperm (male gametes), which are discharged within the embryo sac. Both sperm fuse with nuclei in the embryo sac. One fertilizes the egg to form the zygote. The other combines with the two polar nuclei to form a triploid nucleus in the central cell, which will give rise to the endosperm, a food-storing tissue of the seed. The endosperm provides nutrients to the developing embryo. In most monocots and some dicots, the endosperm also stores nutrients that can be used by the seedling after germination.
Double fertilization ensures that the endosperm will develop only in ovules where the egg has been fertilized, thus preventing angiosperms from squandering nutrients.
13. The self-incompatibility systems in plant are analogous to the immune response of animals. Both are based on the ability of organisms to distinguish “self” from “nonself.” The key difference is that the animal immune system rejects nonself, but self-incompatibility in plants is a rejection of self.
14. The union of two sperm cells with different nuclei of the embryo sac is termed double fertilization. After double fertilization, the ovule develops into a seed, and the ovary develops into a fruit enclosing the seed(s). As the embryo develops, the seed stockpiles proteins, oils, and starch. Initially, these nutrients are stored in the endosperm. Later in seed development in many species, the storage function is taken over by the swelling storage leaves (cotyledons) of the embryo itself.
15. Endosperm development usually precedes embryo development. After double fertilization, the triploid nucleus of the ovule’s central cell divides, forming a multinucleate “supercell” having a milky consistency. It becomes multicellular when cytokinesis partitions the cytoplasm between nuclei. Cell walls form, and the endosperm becomes solid. Coconut “milk” is an example of liquid endosperm and coconut “meat” is an example of solid endosperm.
16. The first mitotic division of the zygote is transverse, splitting the fertilized egg into a basal cell and a terminal cell. The terminal cell gives rise to most of the embryo. The basal cell continues to divide transversely, producing a thread of cells, the suspensor, which anchors the embryo to its parent. The suspensor functions in the transfer of nutrients to the embryo from the parent. The terminal cell divides several times and forms a spherical proembryo attached to the suspensor. Cotyledons begin to form as bumps on the proembryo. After the cotyledons appear, the embryo elongates. Cradled between cotyledons is the embryonic shoot apex with the apical meristem of the embryonic shoot. At the opposite end of the embryo axis is the apex of the embryonic root, also with a meristem. After the seed germinates, the apical meristems at the tips of the shoot and root sustain primary growth as long as the plant lives. During the last stages of maturation, a seed dehydrates until its water content is only about 5–15% of its weight. The embryo stops growing and becomes dormant until the seed germinates. The embryo and its food supply are enclosed by a protective seed coat formed by the integuments of the ovule.
17. Describe the development of a plant embryo from the first mitotic division to the embryonic plant with rudimentary organs.
After double fertilization occurs, the 1st mitotic division of the zygote (transverse) splits the fertilized egg into a basal cell and a terminal cell. The terminal cell gives rise to most of the embryo. The basal cell continues to divide (transversely), and produces a thread of cells, the suspensor, which anchor the embryo to its parent and functions in the transfer of nutrients to the embryo from the parent. The terminal cell divides several times and forms a spherical proembryo attached to the suspensor. Bumps on the proembryo turn into cotyledons (dicots have two and look heart-shaped at this stage, monocots only have one). Then, the embryo elongates. The shoot apex with the apical meristem grows between the cotyledons. At the opposite end of the embryo axis is the apex of the embryonic root, with its own meristem. After the seed germinates, the apical meristems at the root and shoot tips sustain primary growth as long as the plant lives.
During the last stages of maturation, a seed will dehydrate itself until its water content is only 55-15% of its weight. Growth stops and the seed becomes dormant. The embryo and its food supply are enclosed by a protective seed coat formed by the integuments of the ovule.
18. The seed coat, a protective layer of integument formed by the ovule, encloses the embryo and its food supply. The radicle is the embryonic root. The endosperm is a food-storing tissue of the seed, rich in nutrients to feed to developing embryo. The embryo is a structure in seeds that generally consists of an elongate structure (the embryonic axis), which is attached to fleshy cotyledons. Cotyledons are storage leaves of the embryo. They absorb nutrients from the endosperm and transfer them to the embryo when the seed germinates. Members of the grass family (i.e. maize & wheat), have a specialized cotyledons called scutellums, which are very thin, with a large surface area pressed against the endosperm. Below the point at which the fleshy cotyledons are attached, the embryonic axis is called the hypocotyl. The hypocotyl terminates in the radicle, or embryonic root. Above it is the epicotyl. At the tip of the epicotyl is the plumule, which consists of the shoot tip with a pair of miniature leaves. Cradled between cotyledons is the embryonic shoot apex with the apical meristem of the embryonic shoot.
19. Monocots and dicots seeds differ in many ways. To begin with, their endosperms are not alike. Generally, in monocots (and in some dicots), the endosperm can be used to stored nutrients even after the seed has germinated. Most dicots, however, completely export the food reserves of the endosperm to their cotyledons before seed development has ended. Thus, mature seeds lack endosperms. Secondly, monocot embryos have a single cotyledon, while dicots have two.
20. Fruits are plant ovaries adapted for seed disperal. Generally, however, if no pollination occurs, a fruit will not develop. Instead, the flower will wither and fall off.While seeds develop from ovules, the flowering plant’s ovary develops into a fruit, to protect the enclosed seeds, and aid in their dispersal by wind or animals. The transformation is triggered by hormonal changes after fertilization. The ovary’s walls become the pericarp, the thickened wall of the fruit. Normally, other parts of the flower wither and are shed, but in certain angiosperms, floral parts may contribute to the fruit. For example, in apples, the fleshy part of the fruit is mostly derived from the swollen receptacle, while the core of the apple fruit develops from the ovary. Depending on developmental origin, there are several types of fruits.
- simple = typical fruit derived from a single carpel or several fused carpels... can be fleshy (i.e. peach) or dry (i.e. pea pod)
- aggregate = results from single flower that has more than one carpelà each forms a small fruit à fruitlets are clustered together on a single receptacle (ex: raspberry)
- multiple = develops from a group of flowers tightly clustered together (inflorescence) à when walls of ovaries thicken, they fuse together and form one fruit (ex: pineapple)
Fruits usually ripen about the same time that their seeds are completing development. For dry fruit (i.e. soybean pods), the ripening occurs so that the fruit will open and release the seeds. In fleshy fruits, however, ripening is controlled by complex hormone interactions. The fruit becomes edible and enticing to animals, to help seed dispersal. The fruit’s “pulp” becomes soften due to enzymes that begin digesting components of the cell walls. Color changes will also occur, from green to red, orange, or yellow. Lastly, fruits becomes sweeter, as organic acids or starch molecules are converted to sugar.
22. As a seed matures, it dehydrates and enters a dormancy phase, a condition of extremely low metabolic rate and a suspension of growth and development. Seed dormancy increases the chances that germination will occur at a time and place advantageous to the seedling. Conditions required to break dormancy and resume growth/development vary between species. Some seeds germinate as soon as they are in a suitable environment. Others remain dormant until some specific environmental cue causes them to break dormancy. Where natural fires are common, many seeds require intense heat to break dormancy, allowing them to take advantage of new opportunities and open space. In the desert, many plants germinate only after a substantial rainfall, ensuring enough water to complete development. Small seeds require light for germination, and break dormancy only if they are buried near the soil’s surface. Other seeds require a chemical attack or physical abrasion as they pass through an animal’s digestive tract before they can germinate. The length of time that a dormant seed remains viable and capable of germinating varies from a few days to decades or longer. Most seeds are durable enough to last for a year or two until conditions are favorable for germination. Nongerminated seeds can accumulated for several years. Germination of seeds depends on imbibition, the uptake of water due to the low water potential of the dry seed. This causes the expanding seed to rupture its seed coat and triggers metabolic changes in the embryo that enable it to resume growth. Enzymes begin digesting the storage materials of endosperm or cotyledons, and the nutrients are transferred to the growing regions of the embryo.
23. Variation occur in germination as they occur in breaking dormancy. Different conditions and environments effect the plant’s growth and development process. Generally, however, the first organ to emerge from the germinating seed is the radicle, the embryonic root. Next, the shoot tip must break through the soil surface. In many dicots, a hook forms in the hypocotyl, and growth pushes it aboveground. Stimulated by light, the hypocotyl straightens, raising the cotyledons and epicotyl. As it rises into the air, the epicotyl spreads its first foliage [true] leaves. These expand, become green, and begin making food by photosynthesis. After the cotyledons have transferred all their nutrients to the developing plant, they shrivel and fall off the seedling. Monocots may use use a different method for breaking ground when they germinate. First, the coleoptile (the sheath enclosing/protecting the embryonic shoot) pushes upward through the soil and into the air. The shoot tip then grows straight up through the tunnel provided by the tubular coleoptile. The tough seed gives rise to a fragile seedling. Because this plant is exposed to both animals and the elements, its survival rate is not high. Thus, as a mature parent, it must produce enormous numbers of seeds to compensate for low individual survival. Ample genetic variation is provided for natural selection to screen.
25. Plants can reproduce sexually or asexually. Asexual reproduction is an extension of the capacity of plants for indeterminate growth. Meristematic tissues with dividing undifferentiated cells can sustain or renew growth indefinitely. Parenchyma cells throughout the plant can divide and differentiate into various types of specialized cells. Detached fragments of some plants can develop into whole offspring. In fragmentation, a parent plant separates into parts that re-form into whole plants. *A variation of this process occurs in some dicots, in which the root system of a single parent gives rise to many adventitious shoots that become separate root systems, forming a clone.* A different method of asexual reproduction, called apomixis, is found in dandelions and some other plants. These produce seed without their flowers being fertilized. A diploid cell in the ovule gives rise to the embryo, and the ovules mature into seeds, which are dispersed by the wind. This process combines asexual reproduction and seed dispersal.
Friday, February 22, 2008
AP Biology Ch36 Objectives
Chapter 36 – Transport in Vascular Plants
1. The most important active transport protein in the plasma membrane of plant cells is the proton pump. It hydrolyzes ATP and uses the released energy to pump hydrogen ions (H+) out of the cell. This creates a proton gradient because the H+ concentration is higher outside the cell than inside. It also creates a membrane potential or voltage, a separation of opposite charges across a membrane. Both the concentration gradient and the membrane potential are forms of potential (stored) energy that can be harnessed to perform cellular work. The proton gradient also functions in cotransport, in which the downhill passage of one solute (H+) is coupled with the uphill passage of another, such as NO3- or sucrose. The role of proton pumps in transport is a specific application of the general mechanism called chemiosmosis, a unifying process in cellular energetics. In chemiosmosis, a transmembrane proton gradient links energy-releasing processes to energy-consuming processes.
2. The net uptake or loss of water by a cell occurs by osmosis, the passive transport of water across a membrane. In the case of a plant cell, the direction of water movement depends on solute concentration and physical pressure. The combined effects of solute concentration and pressure are called water potential, represented by the Greek letter “psi.” Plant biologists measure psi in units called megapascals (MPa), where one MPa is equal to about 10 atmospheres of pressure. An atmosphere is the pressure exerted at sea level by an imaginary column of air—about 1 kg of pressure per square centimeter.
3. Both pressure and solute concentration affect water potential. The combined effects of pressure and solute concentrations on water potential are incorporated into psi = psip + psis, where psip is the pressure potential and psis is the solute potential (or osmotic potential). The addition of solutes lowers the water potential because the solutes bind water molecules, which have less freedom to move than they do in pure water.
4. In a flaccid cell, where the pressure potential is 0, the cell is limp. If this cell is placed in a solution with a higher solute concentration (and, therefore, a lower psi), water will leave the cell by osmosis. Eventually, the cell will plasmolyze by shrinking and pulling away from its wall. If a flaccid cell is placed in pure water (psi = 0), the cell will have lower water potential than pure water due to the presence of solutes, and water will enter the cell by osmosis. As the cell begins to swell, it will push against the cell wall, producing turgor pressure. The partially elastic wall will push back until this pressure is great enough to offset the tendency for water to enter the cell because of solutes. A walled cell with a greater solute concentration than its surroundings will be turgid, or firm.
5. In a flaccid cell, psip = 0 and the cell is limp. The cell will plasmolyze by shrinking and pulling away from its wall when water is leaving the cell by osmosis. Water in living cells is usually under positive pressure. The cell contents press the plasma membrane against the cell wall, producing turgor pressure. A walled cell with a greater solute concentration than its surroundings will be turgid, or firm.
6. Both plant and animal membranes have specific transport proteins, aquaporins, which facilitate the passive movement of water across a membrane. Aquaporins do not affect the water potential gradient or the direction of water flow, but rather increase the rate at which water diffuses down its water potential gradient. Evidence is accumulating that the rate of water movement through aquaporins is regulated by changes in second messengers such as calcium ions (Ca2+). This raises the possibility that the cell can regulate its rate of water uptake or loss when its water potential is different from that of its environment.
7. The three major compartments in vacuolated plants cells are: the cell wall, cytosol, and vacuole.
8. In most plant tissues, two of the three cellular compartments are continuous from cell to cell. Plasmodesmata connect the cytosolic compartments of neighboring cells. This cytoplasmic continuum, the symplast, forms a continuous pathway for transport of certain molecules between cells. The walls of adjacent plant cells are also in contact, forming a second continuous compartment, the apoplast.
9. Three routes are available for lateral transport. In one route, substances move out of one cell, across the cell wall, and into the neighboring cell, which may then pass the substances along to the next cell by the same mechanism (this transmembrane route requires repeated crossings of plasma membranes). The second route, via the symplast, requires only one crossing of a plasma membrane (after entering one cell, solutes and water move from cell to cell via plasmodesmata). The third route is along the apoplast, the extracellular pathway consisting of cell wall and extracellular spaces (water and solutes can move from one location to another within a root or other organ through the continuum of cell walls without ever entering a cell).
10. Diffusion is much too slow for long-distance transport within a plant, such as the movement of water and minerals from roots to leaves. Water and solutes move through xylem vessels and sieve tubes by bulk flow, the movement of a fluid driven by pressure. In phloem, hydrostatic pressure generated at one end of a sieve tube forces sap to the opposite end of the tube. In xylem, it is actually tension (negative pressure) that drives long-distance transport. Transpiration, the evaporation of water from a leaf, reduces pressure in the leaf xylem. This creates a tension that pulls xylem sap upward from the roots.
11. To maximize bulk flow, the sieve-tube members are almost entirely devoid of internal organelles. Vessel elements and tracheids are dead at maturity. The porous plates that connect contiguous sieve-tube members and the perforated end walls of xylem vessel elements also enhance bulk flow.
12. Water and mineral from the soil enter the plant through the epidermis of roots, cross the root cortex, pass into the vascular cylinder, and then flow up xylem vessels to the shoot system. The uptake of soil solution by the hydrophilic epidermal walls of root hairs provides access to the apoplast, and water and minerals can soak into the cortex along this route. Minerals and water that cross the plasma membranes of root hairs enter the symplast. Some water and minerals are transported into cells of the epidermis and cortex and then move inward via the symplast. Materials flowing along the apoplastic route are blocked by the waxy Casparian strip at the endodermis. Some minerals detour around the Casparian strip by crossing the plasma membrane of an endodermal cell to pass into the vascular cylinder. Endodermal and parenchyma cells within the vascular cylinder discharge water and minerals into their walls (apoplast). The water and minerals enter the dead cells of xylem vessels and are transported upward into the shoots.
13. The mycorrhizae create an enormous surface area for absorption and enable older regions of the roots to supply water and minerals to the plant.
14. The endodermis, with it’s Casparian strip, functions as a selective barrier between the root cortex and the vascular cylinder by acting as a filter. The flow of materials is blocked by the waxy Casparian strip. Only certain minerals can cross by using the plasma membrane of an endodermal cell to pass into the vascular cylinder.
15. Root cells pump mineral ions into the xylem, where they accumulate in the vascular cylinder. Consequentially, water potential is lowered [in the cylinders]. When the water potential lowers, it forces fluid up the xylem. This force is called root pressure. Root pressure helps xylem sap travel upwards in trees against gravity. However, it is not the major mechanism driving ascent of xylem sap, because root pressure can only force water up a few meters at a time. In addition, many plants do not generate root pressure.
16. Transpiration is the evaporation of water from a leaf. It is the main mechanism driving the ascent of xylem sap. Guttation is the exudation of water droplets that can be seen in the morning on the tips of grass blades or the leaf margins of some small, herbaceous dicots as a result of root pressure.
17. Transpiration, in simple terms, reduces pressure in the leaf xylem, and creates a tension that pulls xylem sap upward from the roots. The tension created by transpiration, however, only causes movement of water because of water’s properties of cohesion and adhesion (caused by hydrogen bonding), which transmit the upward pull along the entire length of the xylem to the roots.
Negative pressure or tension must be generated in order for transpiration to occur. Water’s physical properties are also an important factor. Water’s cohesive properties due to hydrogen bonding makes it possible to pull a column of sap up. Water’s adhesion to the hydrophilic walls of the xylem cells help fight the force of gravity. Also, the very small diameter of the tracheids and vessel elements exposes a large proportion of the water to the hydrophilic walls. *The upward pull on the cohesive sap creates tension within the xylem.
STEPS
- Water transpires from a leaf à Water coating the mesophyll cells replaces water lost from the air spaces
- Transpiring water evaporates à The remaining film of water is drawn back into the cell wall’s pores (due to its attraction to the hydrophilic walls)
- Water’s cohesive properties make it resist an increase in surface area of the film.
- A meniscus forms on the surface of the water due to surface tension and cohesive/adhesive forces.
- The film of water at the surface of the leaf cells has a negative pressure less than that of the atmosphere. The more concavity, the move negative pressure.
- The negative pressure pulls the water out of the leaf xylem, through the mesophyll, towards the cells and surface film bordering the air spaces.
- The tension generated by adhesion and surface tension lowers the water potential, drawing water from an area of high water potential to an area of lower water potential.
- Mesophyll cells lose water to the surface film lining the air spaces, which in turn loses water by transpiration.
- The water lost via the stomata is replaced by water pulled out of the leaf xylem. The transpirational pull on xylem sap is transmitted all the way from the leaves to the root tips and the soil solution.
18. Cavitation is the formation of water vapor pockets in the xylem vessel, and occurs when xylem sap freezes in water. Cavitation prevents the transport of water through xylem vessels because it breaks the chain of H2O. Transpirational pull can only extend down to the roots through an unbroken chain of water molecules.
19. The movement of xylem sap upwards is ultimately solar-powered bulk flow. The fluid’s ascent is basically long-distance transport, driven by a water potential difference at opposite ends of xylem vessels of chains of tracheids (called conduits, in general). No metabolic energy is used to lift xylem sap up to the leaves. Sunlight absorbed by the plants drives transpiration and evaporation of water from the walls of a plant’s mesophyll cells. The water potential differences generated by transpirational pull at the leaf end, which also lowers the water potential at the “upstream” end of the xylem (in the leaves’ air spaces lowers). This lowering of water potential increases tension. Water potential drives the osmotic movement of water from cell to cell within the root and leaf tissue. Differences in solution concentration and turgor pressure are also factors in water movement. However, in bulk flow, pressure is the only mechanism for long-distance transport up xylem vessels, and the whole solution is moved—the solvent and the solutes.
20. An extensive inner surface area of a leaf is both important and costly. Generally, leaves have have broad surface areas and high ratios of surface area to volume to enhance the absorption of light for photosynthesis. This, however, increases water loss through stomata. To make food, a plant must spread its leaves to the sun and obtain CO2 from air. While oxygen diffuses out of the leaf via the stomata, carbon dioxide diffuses into the leaf and enters a honeycomb of air spaces formed by the parenchyma cells (irregularly shaped). This internal surface can be anywhere from 10 to 30 times greater than the external leaf surface in order to increases exposure to CO2 while also increasing the surface area for evaporation.
21. A leaf’s stomatal density is affected by both its environment and its genes. In terms of environment, the heat and humidity of a region are important factors. Plants lose water through their stomata to cool them down. Desert plants have lower stomatal densities than do marsh plants. High light intensities and low carbon dioxide levels during plant development tend to increase stomatal density in many plant species. Increased CO2 levels tend to lead to decreased stomatal density. Changes in the density of the stomata prevent the leaf from reaching temperatures that could denature enzymes.
22. Flanking either side of every stomata, pairs of guard cells are suspended by epidermal cells over air chambers that lead to the internal air space. Guard cells control the stoma’s diameter by changing shape and narrowing or widening the gap between two of them. After water intake through osmosis, these cells become more turgid. Due to the orientation of their cellulose microfibrils, the guard cells buckle outward. When water is lost by the guard cells, they become flaccid and less bowed, and consequentially, the space between them closes.
Guard cells’ role in photosynthesis-transpiration?
23. Stomata open and close based on changes in turgor pressure. Primarily, these changes occur as a result of the loss and uptake of potassium ions (K+) by guard cells. When these ions are actively being accumulated, stomata are open; the water potential in guard cells decreases while their turgor increases due to the inflow of water by osmosis. When K+ ions leave the guard cells, water is lost through osmosis, and the stomata close.
The guard cells’ shrinking/swelling and the stomatal opening/closings maybe also be linked to the regulation of aquaporins, which vary the permeability of the membranes to water. The K+ fluctuations across the guard cell membranes are coupled with the generation of membrane potentials by proton pumps. When stomata are open, H+ ions are being actively transported out of guard cells. The resulting voltage/membrane potential drives K+ into the cell through specific membrane channels.
Stomata are generally open during the day and closed at night to minimize water loss when it is too dark for photosynthesis. Stomata usually open at dawn as a result of 3 cues. Blue-light receptors in the guard cells stimulate proton pumps that work in the uptake of K+. Because the pumps require ATP, light reactions begin to occur, and photosynthesis occurs to create a supply of ATP. CO2 within the mesophyll is depleted by these processes. The internal “clock” of the guard cells regulates the cyclic process and monitors the daily rhythmic opening and closing (this is an example of circadian rhythm, or a cycle with an internal of about 24 hours).
Various environmental stresses, however, can cause stomata to close during the day. If the plant is suffering a water deficiency, turgor in the guard cells may be lost. A hormone called abscisic acid will then be produced by mesophyll cells in response to water deficiency. Guard cells will be given a signal, and the stomata will close. Thus, wilting is stopped and photosynthesis is slowed.
24. Xerophytes are plants that adapted to arid climates by modifying their leaves in various ways that help reduce the rate of transpiration. To begin with, surface area to volume ratios in leaves are reduced. Consequentially, xerophytes have small, thick leaves. In the driest months, some plants shed their leaves, while others live in water stored in their fleshy stems (from the rainy season). Thick cuticles on xerophyte leaves help preventing drying, but also give some plants a leathery consistency. Stomata are located in depressions or crypts that protect the pores from dry wind. Hairs called trichomes also break up air flow and help keep humidity high in the crypt (compared to the surrounding atmosphere).
25. Some xerophytes reduce their transpiration by assimilating CO2 through an alternative photosynthetic pathway, crassulacean acid metabolism (CAM). The mesophyll cells in these CAM plants store CO2 in organic acids during the night, and release the CO2 from these organic acids during the day. Only during the day do CAM plants synthesize sugars, and when doing so, use the conventional (C3) photosynthetic pathway. This process allows stomata to stay closed during day and to prevent great transpiration.
26. Translocation is a process in which the organic products of photosynthesis are transported throughout the plant by the phloem. In angiosperms, the specialized cells of the phloem involved in this process are called the sieve-tube members, and are arranged end to end to form long tubes with porous cross-walls between the cells. Sieve tubes always carry food from a sugar source to a sugar sink. Sugar sources are plant organs (i.e. mature leaves) where sugar is being produced through photosynthesis or starch breakdown. Sugar sinks are organs (i.e. growing roots, shoots, or fruit) that consume or store sugar as well as minerals. Depending on the season, storage organs (i.e. tubers or bulbs) can be sources or sinks. In the summer, they stockpile carbs and are sugar sinks. In the spring, the same organs become sources, as their starches are broken down to sugars and are carried away in the phloem to growing buds of the shoot system. Sieve tubes in the same vascular bundle can carry sap in different directions. The direction of transport depends on the location of the source and sink connected by the tube.
27. Before being exported to sugar sinks, sugar from mesophyll cells (or other sources) must be loaded into sieve-tube members. Depending on the species of the plant, this movement can be via the symplast or by a combination of symplastic and apoplastic pathways. Sucrose can diffuse through the symplast from mesophyll cells into small veins. Much of this sugar moves out of the cells into the apoplast in the vicinity of sieve-tube members and companion cells. Companion cells pass the sugar they accumulate into the sieve-tube members via plasmodesmata. In some plants, companion cells (transfer cells) have numerous ingrowths in their walls to increase the cell’s surface area and enhance the transfer of solutes between apoplast and symplast. Because some sieve-tube members accumulate sucrose of very high concentrations, active transport is required to load the phloem. Proton pumps generate an H+ gradient, which drives sucrose across the membrane via a cotransport protein that couples sucrose transport to the diffusion of H+ back into the cell. Downstream, at the sink end of the sieve tube, phloem unloads its sucrose. The mechanism of phloem unloading is highly variable and depends on plant species and type of organ. Regardless of mechanism, because the concentration of free sugar in the sink is lower than in the phloem, sugar molecules diffuse from the phloem into the sink tissues. Water follows by osmosis.
28. In angiosperms, the mechanism of translocation is called pressure flow. It involves moving phloem sap from sugar sources to sugar sinks by bulk flow driven by positive pressure. Pressure flow moves the sap faster than diffusion or cytoplasmic streaming. Pressure flow in a sieve tube drives the bulk flow of phloem sap. Sugar is loaded into the tube at source. This reduces the water potential inside the sieve-tube members, and causes water uptake. The absorption of water then generates hydrostatic pressure, which forces the sap to flow along the tube. At the sink, pressure is relieved when the sugars are unloaded and water is lost from the tube. In leaf-to-root translocation, water is recycled by the xylem from sink to source.
1. The most important active transport protein in the plasma membrane of plant cells is the proton pump. It hydrolyzes ATP and uses the released energy to pump hydrogen ions (H+) out of the cell. This creates a proton gradient because the H+ concentration is higher outside the cell than inside. It also creates a membrane potential or voltage, a separation of opposite charges across a membrane. Both the concentration gradient and the membrane potential are forms of potential (stored) energy that can be harnessed to perform cellular work. The proton gradient also functions in cotransport, in which the downhill passage of one solute (H+) is coupled with the uphill passage of another, such as NO3- or sucrose. The role of proton pumps in transport is a specific application of the general mechanism called chemiosmosis, a unifying process in cellular energetics. In chemiosmosis, a transmembrane proton gradient links energy-releasing processes to energy-consuming processes.
2. The net uptake or loss of water by a cell occurs by osmosis, the passive transport of water across a membrane. In the case of a plant cell, the direction of water movement depends on solute concentration and physical pressure. The combined effects of solute concentration and pressure are called water potential, represented by the Greek letter “psi.” Plant biologists measure psi in units called megapascals (MPa), where one MPa is equal to about 10 atmospheres of pressure. An atmosphere is the pressure exerted at sea level by an imaginary column of air—about 1 kg of pressure per square centimeter.
3. Both pressure and solute concentration affect water potential. The combined effects of pressure and solute concentrations on water potential are incorporated into psi = psip + psis, where psip is the pressure potential and psis is the solute potential (or osmotic potential). The addition of solutes lowers the water potential because the solutes bind water molecules, which have less freedom to move than they do in pure water.
4. In a flaccid cell, where the pressure potential is 0, the cell is limp. If this cell is placed in a solution with a higher solute concentration (and, therefore, a lower psi), water will leave the cell by osmosis. Eventually, the cell will plasmolyze by shrinking and pulling away from its wall. If a flaccid cell is placed in pure water (psi = 0), the cell will have lower water potential than pure water due to the presence of solutes, and water will enter the cell by osmosis. As the cell begins to swell, it will push against the cell wall, producing turgor pressure. The partially elastic wall will push back until this pressure is great enough to offset the tendency for water to enter the cell because of solutes. A walled cell with a greater solute concentration than its surroundings will be turgid, or firm.
5. In a flaccid cell, psip = 0 and the cell is limp. The cell will plasmolyze by shrinking and pulling away from its wall when water is leaving the cell by osmosis. Water in living cells is usually under positive pressure. The cell contents press the plasma membrane against the cell wall, producing turgor pressure. A walled cell with a greater solute concentration than its surroundings will be turgid, or firm.
6. Both plant and animal membranes have specific transport proteins, aquaporins, which facilitate the passive movement of water across a membrane. Aquaporins do not affect the water potential gradient or the direction of water flow, but rather increase the rate at which water diffuses down its water potential gradient. Evidence is accumulating that the rate of water movement through aquaporins is regulated by changes in second messengers such as calcium ions (Ca2+). This raises the possibility that the cell can regulate its rate of water uptake or loss when its water potential is different from that of its environment.
7. The three major compartments in vacuolated plants cells are: the cell wall, cytosol, and vacuole.
8. In most plant tissues, two of the three cellular compartments are continuous from cell to cell. Plasmodesmata connect the cytosolic compartments of neighboring cells. This cytoplasmic continuum, the symplast, forms a continuous pathway for transport of certain molecules between cells. The walls of adjacent plant cells are also in contact, forming a second continuous compartment, the apoplast.
9. Three routes are available for lateral transport. In one route, substances move out of one cell, across the cell wall, and into the neighboring cell, which may then pass the substances along to the next cell by the same mechanism (this transmembrane route requires repeated crossings of plasma membranes). The second route, via the symplast, requires only one crossing of a plasma membrane (after entering one cell, solutes and water move from cell to cell via plasmodesmata). The third route is along the apoplast, the extracellular pathway consisting of cell wall and extracellular spaces (water and solutes can move from one location to another within a root or other organ through the continuum of cell walls without ever entering a cell).
10. Diffusion is much too slow for long-distance transport within a plant, such as the movement of water and minerals from roots to leaves. Water and solutes move through xylem vessels and sieve tubes by bulk flow, the movement of a fluid driven by pressure. In phloem, hydrostatic pressure generated at one end of a sieve tube forces sap to the opposite end of the tube. In xylem, it is actually tension (negative pressure) that drives long-distance transport. Transpiration, the evaporation of water from a leaf, reduces pressure in the leaf xylem. This creates a tension that pulls xylem sap upward from the roots.
11. To maximize bulk flow, the sieve-tube members are almost entirely devoid of internal organelles. Vessel elements and tracheids are dead at maturity. The porous plates that connect contiguous sieve-tube members and the perforated end walls of xylem vessel elements also enhance bulk flow.
12. Water and mineral from the soil enter the plant through the epidermis of roots, cross the root cortex, pass into the vascular cylinder, and then flow up xylem vessels to the shoot system. The uptake of soil solution by the hydrophilic epidermal walls of root hairs provides access to the apoplast, and water and minerals can soak into the cortex along this route. Minerals and water that cross the plasma membranes of root hairs enter the symplast. Some water and minerals are transported into cells of the epidermis and cortex and then move inward via the symplast. Materials flowing along the apoplastic route are blocked by the waxy Casparian strip at the endodermis. Some minerals detour around the Casparian strip by crossing the plasma membrane of an endodermal cell to pass into the vascular cylinder. Endodermal and parenchyma cells within the vascular cylinder discharge water and minerals into their walls (apoplast). The water and minerals enter the dead cells of xylem vessels and are transported upward into the shoots.
13. The mycorrhizae create an enormous surface area for absorption and enable older regions of the roots to supply water and minerals to the plant.
14. The endodermis, with it’s Casparian strip, functions as a selective barrier between the root cortex and the vascular cylinder by acting as a filter. The flow of materials is blocked by the waxy Casparian strip. Only certain minerals can cross by using the plasma membrane of an endodermal cell to pass into the vascular cylinder.
15. Root cells pump mineral ions into the xylem, where they accumulate in the vascular cylinder. Consequentially, water potential is lowered [in the cylinders]. When the water potential lowers, it forces fluid up the xylem. This force is called root pressure. Root pressure helps xylem sap travel upwards in trees against gravity. However, it is not the major mechanism driving ascent of xylem sap, because root pressure can only force water up a few meters at a time. In addition, many plants do not generate root pressure.
16. Transpiration is the evaporation of water from a leaf. It is the main mechanism driving the ascent of xylem sap. Guttation is the exudation of water droplets that can be seen in the morning on the tips of grass blades or the leaf margins of some small, herbaceous dicots as a result of root pressure.
17. Transpiration, in simple terms, reduces pressure in the leaf xylem, and creates a tension that pulls xylem sap upward from the roots. The tension created by transpiration, however, only causes movement of water because of water’s properties of cohesion and adhesion (caused by hydrogen bonding), which transmit the upward pull along the entire length of the xylem to the roots.
Negative pressure or tension must be generated in order for transpiration to occur. Water’s physical properties are also an important factor. Water’s cohesive properties due to hydrogen bonding makes it possible to pull a column of sap up. Water’s adhesion to the hydrophilic walls of the xylem cells help fight the force of gravity. Also, the very small diameter of the tracheids and vessel elements exposes a large proportion of the water to the hydrophilic walls. *The upward pull on the cohesive sap creates tension within the xylem.
STEPS
- Water transpires from a leaf à Water coating the mesophyll cells replaces water lost from the air spaces
- Transpiring water evaporates à The remaining film of water is drawn back into the cell wall’s pores (due to its attraction to the hydrophilic walls)
- Water’s cohesive properties make it resist an increase in surface area of the film.
- A meniscus forms on the surface of the water due to surface tension and cohesive/adhesive forces.
- The film of water at the surface of the leaf cells has a negative pressure less than that of the atmosphere. The more concavity, the move negative pressure.
- The negative pressure pulls the water out of the leaf xylem, through the mesophyll, towards the cells and surface film bordering the air spaces.
- The tension generated by adhesion and surface tension lowers the water potential, drawing water from an area of high water potential to an area of lower water potential.
- Mesophyll cells lose water to the surface film lining the air spaces, which in turn loses water by transpiration.
- The water lost via the stomata is replaced by water pulled out of the leaf xylem. The transpirational pull on xylem sap is transmitted all the way from the leaves to the root tips and the soil solution.
18. Cavitation is the formation of water vapor pockets in the xylem vessel, and occurs when xylem sap freezes in water. Cavitation prevents the transport of water through xylem vessels because it breaks the chain of H2O. Transpirational pull can only extend down to the roots through an unbroken chain of water molecules.
19. The movement of xylem sap upwards is ultimately solar-powered bulk flow. The fluid’s ascent is basically long-distance transport, driven by a water potential difference at opposite ends of xylem vessels of chains of tracheids (called conduits, in general). No metabolic energy is used to lift xylem sap up to the leaves. Sunlight absorbed by the plants drives transpiration and evaporation of water from the walls of a plant’s mesophyll cells. The water potential differences generated by transpirational pull at the leaf end, which also lowers the water potential at the “upstream” end of the xylem (in the leaves’ air spaces lowers). This lowering of water potential increases tension. Water potential drives the osmotic movement of water from cell to cell within the root and leaf tissue. Differences in solution concentration and turgor pressure are also factors in water movement. However, in bulk flow, pressure is the only mechanism for long-distance transport up xylem vessels, and the whole solution is moved—the solvent and the solutes.
20. An extensive inner surface area of a leaf is both important and costly. Generally, leaves have have broad surface areas and high ratios of surface area to volume to enhance the absorption of light for photosynthesis. This, however, increases water loss through stomata. To make food, a plant must spread its leaves to the sun and obtain CO2 from air. While oxygen diffuses out of the leaf via the stomata, carbon dioxide diffuses into the leaf and enters a honeycomb of air spaces formed by the parenchyma cells (irregularly shaped). This internal surface can be anywhere from 10 to 30 times greater than the external leaf surface in order to increases exposure to CO2 while also increasing the surface area for evaporation.
21. A leaf’s stomatal density is affected by both its environment and its genes. In terms of environment, the heat and humidity of a region are important factors. Plants lose water through their stomata to cool them down. Desert plants have lower stomatal densities than do marsh plants. High light intensities and low carbon dioxide levels during plant development tend to increase stomatal density in many plant species. Increased CO2 levels tend to lead to decreased stomatal density. Changes in the density of the stomata prevent the leaf from reaching temperatures that could denature enzymes.
22. Flanking either side of every stomata, pairs of guard cells are suspended by epidermal cells over air chambers that lead to the internal air space. Guard cells control the stoma’s diameter by changing shape and narrowing or widening the gap between two of them. After water intake through osmosis, these cells become more turgid. Due to the orientation of their cellulose microfibrils, the guard cells buckle outward. When water is lost by the guard cells, they become flaccid and less bowed, and consequentially, the space between them closes.
Guard cells’ role in photosynthesis-transpiration?
23. Stomata open and close based on changes in turgor pressure. Primarily, these changes occur as a result of the loss and uptake of potassium ions (K+) by guard cells. When these ions are actively being accumulated, stomata are open; the water potential in guard cells decreases while their turgor increases due to the inflow of water by osmosis. When K+ ions leave the guard cells, water is lost through osmosis, and the stomata close.
The guard cells’ shrinking/swelling and the stomatal opening/closings maybe also be linked to the regulation of aquaporins, which vary the permeability of the membranes to water. The K+ fluctuations across the guard cell membranes are coupled with the generation of membrane potentials by proton pumps. When stomata are open, H+ ions are being actively transported out of guard cells. The resulting voltage/membrane potential drives K+ into the cell through specific membrane channels.
Stomata are generally open during the day and closed at night to minimize water loss when it is too dark for photosynthesis. Stomata usually open at dawn as a result of 3 cues. Blue-light receptors in the guard cells stimulate proton pumps that work in the uptake of K+. Because the pumps require ATP, light reactions begin to occur, and photosynthesis occurs to create a supply of ATP. CO2 within the mesophyll is depleted by these processes. The internal “clock” of the guard cells regulates the cyclic process and monitors the daily rhythmic opening and closing (this is an example of circadian rhythm, or a cycle with an internal of about 24 hours).
Various environmental stresses, however, can cause stomata to close during the day. If the plant is suffering a water deficiency, turgor in the guard cells may be lost. A hormone called abscisic acid will then be produced by mesophyll cells in response to water deficiency. Guard cells will be given a signal, and the stomata will close. Thus, wilting is stopped and photosynthesis is slowed.
24. Xerophytes are plants that adapted to arid climates by modifying their leaves in various ways that help reduce the rate of transpiration. To begin with, surface area to volume ratios in leaves are reduced. Consequentially, xerophytes have small, thick leaves. In the driest months, some plants shed their leaves, while others live in water stored in their fleshy stems (from the rainy season). Thick cuticles on xerophyte leaves help preventing drying, but also give some plants a leathery consistency. Stomata are located in depressions or crypts that protect the pores from dry wind. Hairs called trichomes also break up air flow and help keep humidity high in the crypt (compared to the surrounding atmosphere).
25. Some xerophytes reduce their transpiration by assimilating CO2 through an alternative photosynthetic pathway, crassulacean acid metabolism (CAM). The mesophyll cells in these CAM plants store CO2 in organic acids during the night, and release the CO2 from these organic acids during the day. Only during the day do CAM plants synthesize sugars, and when doing so, use the conventional (C3) photosynthetic pathway. This process allows stomata to stay closed during day and to prevent great transpiration.
26. Translocation is a process in which the organic products of photosynthesis are transported throughout the plant by the phloem. In angiosperms, the specialized cells of the phloem involved in this process are called the sieve-tube members, and are arranged end to end to form long tubes with porous cross-walls between the cells. Sieve tubes always carry food from a sugar source to a sugar sink. Sugar sources are plant organs (i.e. mature leaves) where sugar is being produced through photosynthesis or starch breakdown. Sugar sinks are organs (i.e. growing roots, shoots, or fruit) that consume or store sugar as well as minerals. Depending on the season, storage organs (i.e. tubers or bulbs) can be sources or sinks. In the summer, they stockpile carbs and are sugar sinks. In the spring, the same organs become sources, as their starches are broken down to sugars and are carried away in the phloem to growing buds of the shoot system. Sieve tubes in the same vascular bundle can carry sap in different directions. The direction of transport depends on the location of the source and sink connected by the tube.
27. Before being exported to sugar sinks, sugar from mesophyll cells (or other sources) must be loaded into sieve-tube members. Depending on the species of the plant, this movement can be via the symplast or by a combination of symplastic and apoplastic pathways. Sucrose can diffuse through the symplast from mesophyll cells into small veins. Much of this sugar moves out of the cells into the apoplast in the vicinity of sieve-tube members and companion cells. Companion cells pass the sugar they accumulate into the sieve-tube members via plasmodesmata. In some plants, companion cells (transfer cells) have numerous ingrowths in their walls to increase the cell’s surface area and enhance the transfer of solutes between apoplast and symplast. Because some sieve-tube members accumulate sucrose of very high concentrations, active transport is required to load the phloem. Proton pumps generate an H+ gradient, which drives sucrose across the membrane via a cotransport protein that couples sucrose transport to the diffusion of H+ back into the cell. Downstream, at the sink end of the sieve tube, phloem unloads its sucrose. The mechanism of phloem unloading is highly variable and depends on plant species and type of organ. Regardless of mechanism, because the concentration of free sugar in the sink is lower than in the phloem, sugar molecules diffuse from the phloem into the sink tissues. Water follows by osmosis.
28. In angiosperms, the mechanism of translocation is called pressure flow. It involves moving phloem sap from sugar sources to sugar sinks by bulk flow driven by positive pressure. Pressure flow moves the sap faster than diffusion or cytoplasmic streaming. Pressure flow in a sieve tube drives the bulk flow of phloem sap. Sugar is loaded into the tube at source. This reduces the water potential inside the sieve-tube members, and causes water uptake. The absorption of water then generates hydrostatic pressure, which forces the sap to flow along the tube. At the sink, pressure is relieved when the sugars are unloaded and water is lost from the tube. In leaf-to-root translocation, water is recycled by the xylem from sink to source.
AP Biology Ch33 Objectives
Chapter 33 - Invertebrates
1. Parts of a Sponge
spongocoel- water is drawn through the pores into this central cavity
porocyte- cell with pores that allow water into the sponge
epidermis- layer of cells that covers the outer surface of the sponge
choanocyte- cholar cells; create a flow of water through the sponge with their flagella and trap food with their collars
mesohyl- gelanitous region separating two cell layers of body of sponge
amoebocyte- wander through mesohyl, take up food from water and from choanocytes, digest it, and carry nutrients to other cells, secrete tough skeletal fibers within the mesohyl
osculum- large opening coming from central cavity, allows water to flow out
spicules- sharp spikes (made of calcium carbonate) located in the mesohyl; form the "skeleton" of many sponges
2. Distinguishing Characteristics of Phylum Cnidaria (hydras, jellies, sea anemones, and coral animals)
- radial symmetry
- gastrovascular cavity
- cnidocytes
o have batteries that may help with defense/attack
o can inject poison, stick to, or entangle the target
- mostly marine
- relatively simple body construction
o diploblastic
o sac with central digestive compartment
o single opening functions as both mouth and anus
o two variations
§ sessile polyp
· adhere to the substratum by the aboral end
· extend their tentacles, waiting for prey
§ floating medusa
· flattened, mouth-down versions of polyps
· move by drifting passively and contracting
· bell-shaped bodies
- carnivores à capture prey
- tentacles arranged in a ring
- nuscles and nerves exist in simplest forms
- four major classes: Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa
· Most hydrozoans alternate polyp and medusa forms, as in the life cycle of Obelia.
° The polyp stage, often a colony of interconnected polyps, is more conspicuous than the medusa.
· Hydras, among the few freshwater cnidarians, are unusual members of the class Hydrozoa in that they exist only in the polyp form.
° When environmental conditions are favorable, a hydra reproduces asexually by budding, the formation of outgrowths that pinch off from the parent to live independently.
° When environmental conditions deteriorate, hydras form resistant zygotes that remain dormant until conditions improve.
· The medusa generally prevails in the life cycle of class Scyphozoa.
° The medusae of most species live among the plankton as jellies.
· Most coastal scyphozoans go through small polyp stages during their life cycle.
° Jellies that live in the open ocean generally lack the sessile polyp.
· Cubozoans have a box-shaped medusa stage.
° They can be distinguished from scyphozoans in other significant ways, such as having complex eyes in the fringe of the medusae.
· Cubozoans, which generally live in tropical oceans, are often equipped with highly toxic cnidocytes.
· Sea anemones and corals belong to the class Anthozoa.
° They occur only as polyps.
° Coral animals live as solitary or colonial forms and secrete a hard external skeleton of calcium carbonate.
° Each polyp generation builds on the skeletal remains of earlier generations to form skeletons that we call coral.
· In tropical seas, coral reefs provide habitat for a great diversity of invertebrates and fishes.
3. Specialized cells found in cnidaria include cells of the epidermis and gastrodermis, which have bundles of microfilaments arranged into contractile fibers. Cnidarians also have muscles and nerves (in very simple forms). Their movements are controlled by their noncentralized nerve net and simple sensory receptors
4. The two basic body plans in Cnidaria are sessile polyps and floating medusas. The cylindrical polyps, such as hydras and sea anemones, use their aboral ends to adhere to their substratum. They wait for their prey with extended tentacles. The medusas are flattened, mouth-down versions of polyps that move by drifting passively and by contracting their bell-shaped bodies. Some cnidarians exist only as polyps, while others exist only as medusas. Some pass sequentially through both a medusa stage and a polyp stage in their life cycle.
5. Four Classes of Cnidaria
- Hydrozoa
o alternate polyp and medusa forms
o colony of interconnected polyps is more conspicuous than medusa
o favorable environmental conditions à asexual reproduction through budding
o bad conditions à hydras form resistant zygotes that remain dormant until conditions improve
- Scyphozoa
o medusa generally prevails in the life cycle
o small polyp stages
- Cubozoans
o boxed shaped medusa stage
o complex eyes embedded
o often have highly toxic cnidocytes
- Anthozoas
o occur only as polyps
o each generation builds on skeletal remains of earlier generations
o form skeletons called coral
o provide habitat for a great diversity of invertebrates and fishes
6. The term diploblastic refers to an animal with only 2 germ layers, such as the cnidarian. An animal with 3 germ layers is triploblastic.
Coeloms form from mesoderm tissue. Animals with a true coelom are known as coelomates. Animals that lack a coelom are known as acoelomates. They have a solid bodies without body cavities.
A gastrovascular cavity is a central digestive compartment while an alimentary canal is a digestive tract with a separate mouth and anus.
Protostomes undergo spiral cleavage, in which planes of cell division are diagonal to the vertical axis of the embryo. Some protostomes also show determinate cleavage, where the fate of each embryonic cell is determined early in development. Many deuterostomes undergo radial cleavage in which the cleavage planes are parallel or perpendicular to the vertical egg axis. Most deuterostomes show indeterminate cleavage, whereby each cell in the early embryo retains the capacity to develop into a complete embryo.
7. Distinguishing Characteristics of Platyhelminthes
- live in marine, freshwater, and damp terrestrial habitats
- thin bodies, ranging in size
- triploblastic
o middle embryonic tissue layer (a mesoderm)
o contributes to more complex organs/organ systems and to true muscle tissue
- gastrovascular cavity with only one opening
- lack a coelom
- flat shape
o places cells close to surrounding water
o enables gas exchange & elimination of nitrogenous wastes (ammonia) by diffusion across body surface
- no specialized organs for gas exchange/circulation
- relatively simple excretory apparatus mainly maintains osmotic balance
8. Four Classes of Platyhelminthes
- Turbellaria (planarians)
o nearly all free-living/nonparasitic
o mostly marine
o carnivores or scavengers
o move using cilia on ventral epidermis
o glide along secreted film of mucus
o muscles can be used for undulatory swimming
o pair of eyespots detect light
o lateral flaps function mainly for smell
o nervous system = complex & centralized à able to modify responses to stimuli
o reproduce asexually through regeneration (parent constricts in the middle, each half regenerates the missing end)
o able to reproduce sexually (hermaphrodites cross-fertilize)
- Monogenia
o parasites in/on host
o tough protective covering
o suckers help with attachment
o large reproductive organs take up most of body
o mostly external parasites of fishes
o simple life cycles
§ ciliated, free-living larva that infects host
- Trematoda
o parasites in/on wide range of hosts
o suckers help with attachment
o complex life cycles with alternation of sexual & asexual stages
§ many need intermediate host for larvae development
§ adult worm appears in final host (normally vertebrate)
§ large reproductive organs take up most of body
o release molecules that manipulate the host’s immune system
o tough protective covering
- Cestoidea (tapeworms)
o parasitic, mostly in vertebrates, including humans
o scolex, suckers and hooks on head, anchor worm in host’s digestive tract
o lack a gastrovascular cavity à absorb food particles
o series of proglottids, sacs of sex organs, lie posterior to the scolex
§ eggs develop into larvae à encyst hosts’s muscles
§ larvae develop into mature adults
§ mature proglottids= loaded with thousands of eggs
§ mature worms release eggs from posterior end
§ eggs leave with host’s feces
9. Trematodes live as parasites in or on other animals, and have very complicated life cycles. Most species have alternations of sexual and asexual stages. They require an intermediate host where the larvae can develop before being able to infect a final host (usually a vertebrate) where the adult worms lives. The blood fluke, Schistosoma, is an example of one such parasite. This organisms causes body pains and dysentery. It uses snails as an intermediate host before infecting humans. Thus, it must evade the immune systems of two very different hosts. These blood flukes create a partial immunological camouflage by mimicking their host’s surface proteins. They are also able to release molecules that manipulate the host’s immune system.
10. Trematodes evade detection by mimicking their host’s surface proteins and releasing molecules that manipulate the host’s immune system. Thus, they create a partial immunological camouflage
11. Tapeworms, of the class Cestoidea, are parasitic. They are mostly invertebrates and live mostly in vertebrates. They have suckers and hooks on the head, or scolex, which anchor them in the digestive tract of their host. They lack a gastrovascular cavity, but absorb food particles from their host. A long series of proglottids, sacs of sex organs, lie posterior to the scolex. Mature proglottids loaded with thousands of eggs are released from the posterior end of the tapeworm and leave with the host’s feces. The eggs are then ingested by intermediary hosts, such as pig and cattle. The eggs develop into larvae that encyst in the muscle of the host. Undercooked meat may cause the cysts to be transferred to the human where the larvae develop into mature adults inside the body.
12. Rotifers are tiny animals (ranging in size from 5 µm to 2 mm), most of which live in freshwater. They are smaller than many protists but are truly multicellular, with specialized organ systems. Rotifers have an alimentary canal, a digestive tract with a separate mouth and anus. Internal organs lie in the pseudocoelom, a body cavity that is not completely lined with mesoderm. The fluid in the pseudocoelom serves as a hydrostatic skeleton. Through the movements of nutrients and wastes dissolved in the coelomic fluid, the pseudocoelom also functions as a circulatory system. The word rotifer refers to the crown of cilia that draws a vortex of water into the mouth. Food particles drawn in by the cilia are captured by the jaws (trophi) in the pharynx and ground up. Some rotifers exist only as females that produce more females from unfertilized eggs, a type of parthenogenesis. Other species produce two types of eggs that develop by parthenogenesis. One type forms females, and the other forms degenerate males that survive just long enough to fertilize eggs. The zygote forms a resistant stage that can withstand environmental extremes until conditions improve. The zygote then begins a new female generation that reproduces by parthenogenesis until conditions become unfavorable again.
13. Parthenogenesis is a type of reproduction where the female produces offspring from unfertilized eggs. Some rotifers produce more females from unfertilized eggs; some produce two types of eggs. One forms females and the other forms degenerate males that survive just long enough to fertilize eggs. Species that reproduce asexually tend to accumulate harmful mutations in their genomes faster than sexually reproducing species. As a result, asexual species experience higher rates of extinction and lower rates of speciation. It is puzzling that so many rotifers survive without males.
14. Lophophores are horseshoes-shaped or circular fold of the body wall bearing ciliated tentacles that surround and draw water towards the mouth. Tentacles trap suspended food particles. There are three lophophore phyla: Ectoprocta, Phoronida, and Brachiopoda.
15. Nemertea have bodies much like flatworms. However, they have small fluid-filled sacs that may be a reduced version of a true coelom. The sac and fluid hydraulics operate an extensible proboscis, which the worm uses to capture prey. These organisms have an alimentary canal and a closed circulatory system in which the blood is contained in vessels. Nemerteans have no heart, and the blood is propelled by muscles squeezing the vessels. Nearly all nemerteans are marine.
16. Nemerteans and flatworms have very similar bodies. They have similar excretory, sensory, and nervous systems. However, what separates Nemerteans from flatworms is that they have an alimentary canal and a closed circuit system where blood is contained in vessels. Nemerteans have small fluid-filled sacs that may be a reduced version of a true coelom. Nemerteans also have no heart, the blood is propelled by muscles squeezing the vessels
17. Mollusca is an invertebrate phyla that includes snails and slugs, oysters and clams, and octopuses and squids. There are several characteristics that distinguishing them from other animal phyla.
- generally marine, but some may have fresh water or terrestrial habitat
- soft bodied... most protected by hard shell made of calcium carbonate (some shells have been lost/reduced in evolution)
- muscular foot typically for movement
- visceral mass with most of the internal organs
- mantle à secretes shell, drapes over visceral mass, creates water-filled chamber with gills, anus, and excretory pores
- feed using radula, a straplike rasping organ that scrapes up food
- generally have separate sexes, with gonads found in visceral mass*many snails, however, are hermaphrodites
- trochophore (ciliated larva stage) found in life cycle*also in marine annelids and certain lophotrochozoans
18. The basic molluscan body plan has evolved into distinct ways that constitute the 8 classes of the phylum. The are 4 prominent classes.
- Bivalvia (clams, oysters, mussels, and scallops)
o shells divided into 2 halves, hinged at the mid-dorsal line
o powerful adductor muscles close shell tightly for protection
o most = suspension feeders à trap fine particles in mucus that coats their gills
· cilia convey the particles to the mouth
· water flows into mantle cavity through incurrent siphon, passes over gills, exits through excurrent siphon
· generally have sedentary lives
· attach to surface, move using muscular foot or swim (flap shells, jet out water)
o no distinct head or radula
o mantle
· outer edge may have eyes/sensory tentacles
· cavity contains gills used for feeding/gas exchange
- Cephalopoda (squids, octopuses, cuttlefish, and chambered nautiluses)
o ancestors probably were shelled molluscs that took up predatory lifestyle
o only molluscs with closed circulatory system
o have well-developed sense organs and complex brain
o capture prey with long tentacles
o move quickly by contracting mantle cavity, firing stream of water out of excurrent siphon
o foot modified into muscular siphon, parts of tentacles, and head
o mantle covers visceral mass
o shell maybe be reduced/internal/missing
- Gastropoda (snails and slugs)
o make up three-quarters of all living species of molluscs
o shells formation = independent developmental process, generally conical, may be flattened (i.e. abalones)
o radulas used to graze on algae/plants
· in predators, modified to bore holes in the shells or to tear apart tough animal tissues
· teeth can form separate poison darts, which penetrate and stun prey
o have distinct heads with eyes at the tips of tentacles
o movement created by a rippling motion of foot or by cilia
o undergo torsion during embryonic development
· visceral mass is rotated up to 180 degrees
· anus and mantle cavity are above the head (in adults)
· some of the organs that were bilateral are reduced/lost on one side of the body
o aquatic species = gills
o terrestrial species = lining of the mantle cavity functions as lung
- Polyplacophora (chitons)
o oval shaped
o unsegmented bodies
o shells divided into eight dorsal plates
o muscular foot used to grips rock substrates and creep over them
o grazers à used radulas to scrape & ingest algae
19. There are two major characteristics that distinguish Annelida from other animal phyla, being that they have segmented bodies and live in moist habitats (sea, freshwater, damp soil)
20. The phylum Annelida is divided into three classes...
- Oligochaeta
o segmented worms
o named for their relatively sparse chaetae (bristles made of chitin)
o Earthworms
· eat their way through soil and digest it in their ailementary canal à undigested material is egested as castings, which enrich the tilled soil
· cross-fertilizing hermaphrodites
Ø 2 earthworms exchange sperm, separate, store sperm
Ø clitellum (special organ) secretes mucous cocoon
Ø cocoon slides along worm’s body, picking up stored eggs and sperm
· some are asexual and reproduce through fragmentation followed by regeneration
- Polychaeta
o polychaetes = “many setae”
o marine (w/ some exceptions)
o pair of paddle/ridgelike parapodia (“almost feet”)
· function in locomotion
· have several chitinous setae
· rich blood vessel inside function as gills (w/ some exceptions)
- Hirudinea (leeches)
o majority inhabit fresh water
o land leeches move through moist vegetation
o range in size from about 1 to 30 cm
o generally feed on other invertebrates
o some are blood-sucking parasites
· feed by attaching temporarily to host
· use blade-like jaws or enzymes to get through skin to blood
· anesthetic keeps host unaware
· secrete hirudin, an anticoagulant
21. Leeches are able to feed on blood due to their special adaptations, such as their feeding “technique.” To get through their hosts’ skin, leeches are equip with either blade-like jaws or enzymes that they can secrete to get to the blood source. Leeches also secrete anesthetics to keep their hosts unaware, so that they can suck longer and get more blood. Their hirudin secretions also are an adaptation, as they prevent blood from coagulating and allow the leeches to feed longer.
22. Characteristics Distinguishing Nematoda (Roundworms) from Other Wormlike Animals
- tough cuticle coating cylindrical body
o exoskeleton periodically shed
o new one is excreted
- alimentary tract
o use the fluid in their pseudocoelom to transport nutrients
o lack a circulatory system
- move by contracting longitudinal muscles (thrashing motion)
- reproduce sexually
o sexes generally separate
o fertilization = internal
o females can lay over 100,000 eggs per day
o zygote = resistant cell, able to survive harsh conditions
- major role in decomposition/nutrient recycling
- parasitize animals or attack plant roots
23. Over 50 species of nematodes—such as pinworms and hookworms—parasitize humans. For example, Trichinella spiralis is a species of nematodes that causes trichinosis and is acquired by consuming undercooked infected meat. The worms encyst in a variety of human organs, including skeletal muscle. These worms can hijack some of their hosts’ cellular function, thus effecting gene expression and protein coding. Nematodes do have a positive effect on the environment, however. Free-living nematodes help with decomposition and nutrient recycling. Caenorhabditis elegans, a soil organism, is a model organism in developmental biology.
24. Characteristics Distinguishing Anthropods from Other Animal Phyla
- seen as most successful phylum (three reasons in italics)
- diverse
- widely distributed à represented in nearly all habitats in the biosphere
- large population
- body segmentation and jointed appendages
o segments & appendages become specialized for variety of functions
o labor division is efficient among regions
- hard exoskeleton
o body completely covered by cuticle made of protein and chitin
o very strong – offers protection
o provides points of attachment for muscles that move appendages
o relatively impermeable to water – prevent desiccation, provides support
o can be thick & inflexible or thin & flexible – ce dépend
o must be molted during growth
§ new, larger on is secreted = ecdysis
§ animal temporarily vulnerable
- well-developed sense organ
o eyes (vision)
o olfactory receptors (smell)
o antennae (touch & smell)
o generally located at anterior end à shows extensive cephalization
- open circulatory system
o hemolymph fluid propelled by heart through short arteries into sinuses (hemocoel... not a coelom) surrounding tissues & organs
o hemolymph returns to heart through valved pores
- reduced true coelom
- specific organs for gas exchange
o aquatic à gills
§ thin, feathery extensions
§ extensive surface area in contact with water
o terrestrial à specialized internal surfaces
25. Exoskeletons can be advantageous because they are very strong and both provide protection support for the body. They also offer places where muscles can anchor in order to move appendages. Furthermore, exoskeletons are useful because they prevent dessication. However, exoskeletons can also be a disadvantage because they must be molted to accommodate for the growth of the body. During molting, while a new and larger exoskeleton is secreted in ecdysis, the animal is left vulnerable.
26. The hemocoel—sinuses connected to arteries—exists in open circulatory systems. It surrounds tissues and organs and contains hemolymph fluid. The hemocoel is not a coelom; the true coelom is very reduced in most arthropods.
27. It is believed that arthropods diverged early on into four main evolutionary lineages
- Cheliceriformes (sea spiders, horseshoe crabs, scorpions, ticks, spiders)
o named is derived from chelicerae, clawlike feeding appendages that serve as pincers/fangs
o have anterior cephalothorax and posterior abdomen
o lack sensory antennae
o most have simple eyes (with a single lens)
o earliest form was eurypterids (water scorpions) = marine and freshwater predators
o modern forms include sea spiders (pycnogonids) and horseshoe crabs
o living majority = arachnids (includes scorpions, spiders, ticks, mites)
- Myriapods (centipedes and millipedes)
o terrestrial
o millipedes = class Diplopoda
§ two pairs of walking legs on each of trunk segments, formed by two fused segments
§ eat decaying leaves and plant matter
§ among the earliest land animals
o centipedes (class Chilopoda)
§ carnivores
§ head has pair of antennae & three pairs of appendages modified as mouth parts, including jawlike mandibles
§ trunk region segments all have one pair of walking legs
§ poison claws on anteriormost trunk segment
· paralyze prey
· defense
- Hexapods (insects and their wingless, six-legged relatives)
o more species-rich than all other forms of life combined
o in almost all habitats (land, water, air)
o some are able to fly
o diverse mouths
o complex organ systems
§ regionally specialized
§ Malpighian tubules = outpockets of digestive tract, removes metabolic wastes from hemolymph
§ tracheal system (respiration) = branched, chitin-lined, carries O2 from spiracles directly to cells
§ nervous system = ventral nerve cords with several segmental ganglia
· two cords meet in the head
· ganglia from several anterior segments fuse into cerebral ganglion (brain)
· structure is close to the antennae, eyes, and other sense organs
o development through metamorphosis
§ incomplete à young are smaller with different body proportions, molting occurs until adult body and size are reached
§ complete à three stages = larval, pupal, adult
o reproduction usually sexual
§ individuals have separate sexes
§ attracted by color, odor, sound
§ females store sperm in spermatheca, in some cases holding enough sperm from a single mating to last a lifetime
§ eggs laid on food source
o important natural and agricultural pollinators
o carriers for many diseases (i.e. malaria and African sleeping sickness)
- Crustaceans (crabs, lobsters, shrimps, barnacles, and many others)
o most = marine/freshwater environment
o typically have biramous (branched), specialized appendages
§ two pairs of antennae
§ at least three pairs of mouthparts, including hard mandibles
§ walking legs present on thorax
§ appendages for swimming or reproduction found on abdomen
§ able to regenerate lost appendages during molting
o gas exchange differs based on size
§ small à exchange gases across thin areas of the cuticle
§ large à gills used
o open circulatory system
§ heart pumps hemolymph into short arteries and then into sinuses that bathe the organs
§ nitrogenous wastes excreted by diffusion through thin areas of cuticle
§ glands regulate salt balance of hemolymph
o sexual reproduction
§ most species have separate sexes
§ aquatic species have several larval stages
28. Spider have three specialized features. To begin with, they are able to inject poison into their prey to immobilize it. The poison is located in glands on their chelicerae. While consuming their prey, spiders spill some of their digestive juices into the tissues. The liquid is sucked up as their meal. Spiders also carry out gas exchange by book lungs, which are stacked plates with an extensive surface area contained in an internal chamber. Lastly, spiders are able to catch flying insects in their silk webs. The production of the protein occurs in abdominal glands. The silk begins as a liquid, but solidifies as it is spun in fibers by spinnerets. Silk fibers also function as egg covers, drop lines for a rapid escape, and “gift wrapping” for nuptial gifts.
29. Insects vary greatly and are the most species rich phylum because of two main things: their ability to fly and the diversification of their mouthparts. Insect flight evolved during the Carboniferous and Permian periods and what followed was an explosion in insect variety because new adaptive zones opened. Flying also enabled insects to escape predators and find more food and mates.
Then, insect mouthparts began to diversify due to different needs (feeding on gymnosperms and Carboniferous plants). Adaptive radiation occurred.
30. Distinguishing Characteristics of Echinoderms (i.e. sea stars)
- deuterostomes
- radial cleavage à secondary radial symmetry
- development of coelom from archenteron
- formation of anus from blastopore
- water vascular system
o network of hydraulic canals
o have tube feet, branched extensions, that function in movement, feeding, gas exchange
- thin skin covering endoskeleton of hard calcareaou plates
- most are sessile (slow moving marine animals)
- many have skeletals bumps/spines that make them prickly
- sexual reproduction à gametes released by males and females into seawater
- internal & external parts radiate from center (generally as 5 spokes)
- larvae have bilateral symmetry
- adults not perfectly radial
31. Living echinoderms are divided into six classes...
- Asteroidea (sea stars)
o multiple arms radiate from central disk
§ undersides have rows of tube feet
· act like suction disks
· controlled by hydraulic & muscular action
· can grasp substrates and prey, & creep over surfaces
§ able to pull apart bivalves (prey)
o can evert stomach through mouth
o can regernerate limbs
- Ophiuroidea (brittle stars)
o distinct central disk
o long, flexible arms
o tube feet lack suckers
o move by a serpentine lashing of arms
o suspension feeders, scavengers, or predators
- Echinoidea (sea urchins and sand dollars)
o no arms
o five rows of tube feet used for locomotion
o pivoting of long spines also enables movement
o mouths may be ringed with complex jawlike structures
o either spherical or flattened and disk-shaped
- Crinoidea (sea lilies and feather stars)
o lilies attach to substratum by stalks
o feather stars crawl using long, flexible arms
o mouth directed upward (award from substrate)
o arms (for suspension feeding) circle mouth
o very conservative evolution
- Holothuroidea (sea cucumbers)
o lack spines
o very reduced endoskeleton
o elongated oral-aboral axis
o five rows of tube feet à some function as feeding tentacles (suspension or deposit feeding)
- Concentricycloidea (sea daisies)
o discovered in 1986 à only two known species
o bodies = armless, disk-shaped, five-fold symmetry
o less than a centimeter in diameter
o absorb nutrients through the membrane surrounding body
o considered to be highly derived sea stars
32. Chordata are included in a chapter on invertebrates because the phylum does include invertebrate subphyla (although it is only 2 out of many). However, they are linked with Echidnoderms, because both are bilateral deuterostomes.
33. Echidnoderms and Chordates are developmentally similar because they are both bilateral deuterostomia. They are coelomates, with radial cleavage. Also, their coeloms develop from their archenterons and their anuses form from their blastopores.
1. Parts of a Sponge
spongocoel- water is drawn through the pores into this central cavity
porocyte- cell with pores that allow water into the sponge
epidermis- layer of cells that covers the outer surface of the sponge
choanocyte- cholar cells; create a flow of water through the sponge with their flagella and trap food with their collars
mesohyl- gelanitous region separating two cell layers of body of sponge
amoebocyte- wander through mesohyl, take up food from water and from choanocytes, digest it, and carry nutrients to other cells, secrete tough skeletal fibers within the mesohyl
osculum- large opening coming from central cavity, allows water to flow out
spicules- sharp spikes (made of calcium carbonate) located in the mesohyl; form the "skeleton" of many sponges
2. Distinguishing Characteristics of Phylum Cnidaria (hydras, jellies, sea anemones, and coral animals)
- radial symmetry
- gastrovascular cavity
- cnidocytes
o have batteries that may help with defense/attack
o can inject poison, stick to, or entangle the target
- mostly marine
- relatively simple body construction
o diploblastic
o sac with central digestive compartment
o single opening functions as both mouth and anus
o two variations
§ sessile polyp
· adhere to the substratum by the aboral end
· extend their tentacles, waiting for prey
§ floating medusa
· flattened, mouth-down versions of polyps
· move by drifting passively and contracting
· bell-shaped bodies
- carnivores à capture prey
- tentacles arranged in a ring
- nuscles and nerves exist in simplest forms
- four major classes: Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa
· Most hydrozoans alternate polyp and medusa forms, as in the life cycle of Obelia.
° The polyp stage, often a colony of interconnected polyps, is more conspicuous than the medusa.
· Hydras, among the few freshwater cnidarians, are unusual members of the class Hydrozoa in that they exist only in the polyp form.
° When environmental conditions are favorable, a hydra reproduces asexually by budding, the formation of outgrowths that pinch off from the parent to live independently.
° When environmental conditions deteriorate, hydras form resistant zygotes that remain dormant until conditions improve.
· The medusa generally prevails in the life cycle of class Scyphozoa.
° The medusae of most species live among the plankton as jellies.
· Most coastal scyphozoans go through small polyp stages during their life cycle.
° Jellies that live in the open ocean generally lack the sessile polyp.
· Cubozoans have a box-shaped medusa stage.
° They can be distinguished from scyphozoans in other significant ways, such as having complex eyes in the fringe of the medusae.
· Cubozoans, which generally live in tropical oceans, are often equipped with highly toxic cnidocytes.
· Sea anemones and corals belong to the class Anthozoa.
° They occur only as polyps.
° Coral animals live as solitary or colonial forms and secrete a hard external skeleton of calcium carbonate.
° Each polyp generation builds on the skeletal remains of earlier generations to form skeletons that we call coral.
· In tropical seas, coral reefs provide habitat for a great diversity of invertebrates and fishes.
3. Specialized cells found in cnidaria include cells of the epidermis and gastrodermis, which have bundles of microfilaments arranged into contractile fibers. Cnidarians also have muscles and nerves (in very simple forms). Their movements are controlled by their noncentralized nerve net and simple sensory receptors
4. The two basic body plans in Cnidaria are sessile polyps and floating medusas. The cylindrical polyps, such as hydras and sea anemones, use their aboral ends to adhere to their substratum. They wait for their prey with extended tentacles. The medusas are flattened, mouth-down versions of polyps that move by drifting passively and by contracting their bell-shaped bodies. Some cnidarians exist only as polyps, while others exist only as medusas. Some pass sequentially through both a medusa stage and a polyp stage in their life cycle.
5. Four Classes of Cnidaria
- Hydrozoa
o alternate polyp and medusa forms
o colony of interconnected polyps is more conspicuous than medusa
o favorable environmental conditions à asexual reproduction through budding
o bad conditions à hydras form resistant zygotes that remain dormant until conditions improve
- Scyphozoa
o medusa generally prevails in the life cycle
o small polyp stages
- Cubozoans
o boxed shaped medusa stage
o complex eyes embedded
o often have highly toxic cnidocytes
- Anthozoas
o occur only as polyps
o each generation builds on skeletal remains of earlier generations
o form skeletons called coral
o provide habitat for a great diversity of invertebrates and fishes
6. The term diploblastic refers to an animal with only 2 germ layers, such as the cnidarian. An animal with 3 germ layers is triploblastic.
Coeloms form from mesoderm tissue. Animals with a true coelom are known as coelomates. Animals that lack a coelom are known as acoelomates. They have a solid bodies without body cavities.
A gastrovascular cavity is a central digestive compartment while an alimentary canal is a digestive tract with a separate mouth and anus.
Protostomes undergo spiral cleavage, in which planes of cell division are diagonal to the vertical axis of the embryo. Some protostomes also show determinate cleavage, where the fate of each embryonic cell is determined early in development. Many deuterostomes undergo radial cleavage in which the cleavage planes are parallel or perpendicular to the vertical egg axis. Most deuterostomes show indeterminate cleavage, whereby each cell in the early embryo retains the capacity to develop into a complete embryo.
7. Distinguishing Characteristics of Platyhelminthes
- live in marine, freshwater, and damp terrestrial habitats
- thin bodies, ranging in size
- triploblastic
o middle embryonic tissue layer (a mesoderm)
o contributes to more complex organs/organ systems and to true muscle tissue
- gastrovascular cavity with only one opening
- lack a coelom
- flat shape
o places cells close to surrounding water
o enables gas exchange & elimination of nitrogenous wastes (ammonia) by diffusion across body surface
- no specialized organs for gas exchange/circulation
- relatively simple excretory apparatus mainly maintains osmotic balance
8. Four Classes of Platyhelminthes
- Turbellaria (planarians)
o nearly all free-living/nonparasitic
o mostly marine
o carnivores or scavengers
o move using cilia on ventral epidermis
o glide along secreted film of mucus
o muscles can be used for undulatory swimming
o pair of eyespots detect light
o lateral flaps function mainly for smell
o nervous system = complex & centralized à able to modify responses to stimuli
o reproduce asexually through regeneration (parent constricts in the middle, each half regenerates the missing end)
o able to reproduce sexually (hermaphrodites cross-fertilize)
- Monogenia
o parasites in/on host
o tough protective covering
o suckers help with attachment
o large reproductive organs take up most of body
o mostly external parasites of fishes
o simple life cycles
§ ciliated, free-living larva that infects host
- Trematoda
o parasites in/on wide range of hosts
o suckers help with attachment
o complex life cycles with alternation of sexual & asexual stages
§ many need intermediate host for larvae development
§ adult worm appears in final host (normally vertebrate)
§ large reproductive organs take up most of body
o release molecules that manipulate the host’s immune system
o tough protective covering
- Cestoidea (tapeworms)
o parasitic, mostly in vertebrates, including humans
o scolex, suckers and hooks on head, anchor worm in host’s digestive tract
o lack a gastrovascular cavity à absorb food particles
o series of proglottids, sacs of sex organs, lie posterior to the scolex
§ eggs develop into larvae à encyst hosts’s muscles
§ larvae develop into mature adults
§ mature proglottids= loaded with thousands of eggs
§ mature worms release eggs from posterior end
§ eggs leave with host’s feces
9. Trematodes live as parasites in or on other animals, and have very complicated life cycles. Most species have alternations of sexual and asexual stages. They require an intermediate host where the larvae can develop before being able to infect a final host (usually a vertebrate) where the adult worms lives. The blood fluke, Schistosoma, is an example of one such parasite. This organisms causes body pains and dysentery. It uses snails as an intermediate host before infecting humans. Thus, it must evade the immune systems of two very different hosts. These blood flukes create a partial immunological camouflage by mimicking their host’s surface proteins. They are also able to release molecules that manipulate the host’s immune system.
10. Trematodes evade detection by mimicking their host’s surface proteins and releasing molecules that manipulate the host’s immune system. Thus, they create a partial immunological camouflage
11. Tapeworms, of the class Cestoidea, are parasitic. They are mostly invertebrates and live mostly in vertebrates. They have suckers and hooks on the head, or scolex, which anchor them in the digestive tract of their host. They lack a gastrovascular cavity, but absorb food particles from their host. A long series of proglottids, sacs of sex organs, lie posterior to the scolex. Mature proglottids loaded with thousands of eggs are released from the posterior end of the tapeworm and leave with the host’s feces. The eggs are then ingested by intermediary hosts, such as pig and cattle. The eggs develop into larvae that encyst in the muscle of the host. Undercooked meat may cause the cysts to be transferred to the human where the larvae develop into mature adults inside the body.
12. Rotifers are tiny animals (ranging in size from 5 µm to 2 mm), most of which live in freshwater. They are smaller than many protists but are truly multicellular, with specialized organ systems. Rotifers have an alimentary canal, a digestive tract with a separate mouth and anus. Internal organs lie in the pseudocoelom, a body cavity that is not completely lined with mesoderm. The fluid in the pseudocoelom serves as a hydrostatic skeleton. Through the movements of nutrients and wastes dissolved in the coelomic fluid, the pseudocoelom also functions as a circulatory system. The word rotifer refers to the crown of cilia that draws a vortex of water into the mouth. Food particles drawn in by the cilia are captured by the jaws (trophi) in the pharynx and ground up. Some rotifers exist only as females that produce more females from unfertilized eggs, a type of parthenogenesis. Other species produce two types of eggs that develop by parthenogenesis. One type forms females, and the other forms degenerate males that survive just long enough to fertilize eggs. The zygote forms a resistant stage that can withstand environmental extremes until conditions improve. The zygote then begins a new female generation that reproduces by parthenogenesis until conditions become unfavorable again.
13. Parthenogenesis is a type of reproduction where the female produces offspring from unfertilized eggs. Some rotifers produce more females from unfertilized eggs; some produce two types of eggs. One forms females and the other forms degenerate males that survive just long enough to fertilize eggs. Species that reproduce asexually tend to accumulate harmful mutations in their genomes faster than sexually reproducing species. As a result, asexual species experience higher rates of extinction and lower rates of speciation. It is puzzling that so many rotifers survive without males.
14. Lophophores are horseshoes-shaped or circular fold of the body wall bearing ciliated tentacles that surround and draw water towards the mouth. Tentacles trap suspended food particles. There are three lophophore phyla: Ectoprocta, Phoronida, and Brachiopoda.
15. Nemertea have bodies much like flatworms. However, they have small fluid-filled sacs that may be a reduced version of a true coelom. The sac and fluid hydraulics operate an extensible proboscis, which the worm uses to capture prey. These organisms have an alimentary canal and a closed circulatory system in which the blood is contained in vessels. Nemerteans have no heart, and the blood is propelled by muscles squeezing the vessels. Nearly all nemerteans are marine.
16. Nemerteans and flatworms have very similar bodies. They have similar excretory, sensory, and nervous systems. However, what separates Nemerteans from flatworms is that they have an alimentary canal and a closed circuit system where blood is contained in vessels. Nemerteans have small fluid-filled sacs that may be a reduced version of a true coelom. Nemerteans also have no heart, the blood is propelled by muscles squeezing the vessels
17. Mollusca is an invertebrate phyla that includes snails and slugs, oysters and clams, and octopuses and squids. There are several characteristics that distinguishing them from other animal phyla.
- generally marine, but some may have fresh water or terrestrial habitat
- soft bodied... most protected by hard shell made of calcium carbonate (some shells have been lost/reduced in evolution)
- muscular foot typically for movement
- visceral mass with most of the internal organs
- mantle à secretes shell, drapes over visceral mass, creates water-filled chamber with gills, anus, and excretory pores
- feed using radula, a straplike rasping organ that scrapes up food
- generally have separate sexes, with gonads found in visceral mass*many snails, however, are hermaphrodites
- trochophore (ciliated larva stage) found in life cycle*also in marine annelids and certain lophotrochozoans
18. The basic molluscan body plan has evolved into distinct ways that constitute the 8 classes of the phylum. The are 4 prominent classes.
- Bivalvia (clams, oysters, mussels, and scallops)
o shells divided into 2 halves, hinged at the mid-dorsal line
o powerful adductor muscles close shell tightly for protection
o most = suspension feeders à trap fine particles in mucus that coats their gills
· cilia convey the particles to the mouth
· water flows into mantle cavity through incurrent siphon, passes over gills, exits through excurrent siphon
· generally have sedentary lives
· attach to surface, move using muscular foot or swim (flap shells, jet out water)
o no distinct head or radula
o mantle
· outer edge may have eyes/sensory tentacles
· cavity contains gills used for feeding/gas exchange
- Cephalopoda (squids, octopuses, cuttlefish, and chambered nautiluses)
o ancestors probably were shelled molluscs that took up predatory lifestyle
o only molluscs with closed circulatory system
o have well-developed sense organs and complex brain
o capture prey with long tentacles
o move quickly by contracting mantle cavity, firing stream of water out of excurrent siphon
o foot modified into muscular siphon, parts of tentacles, and head
o mantle covers visceral mass
o shell maybe be reduced/internal/missing
- Gastropoda (snails and slugs)
o make up three-quarters of all living species of molluscs
o shells formation = independent developmental process, generally conical, may be flattened (i.e. abalones)
o radulas used to graze on algae/plants
· in predators, modified to bore holes in the shells or to tear apart tough animal tissues
· teeth can form separate poison darts, which penetrate and stun prey
o have distinct heads with eyes at the tips of tentacles
o movement created by a rippling motion of foot or by cilia
o undergo torsion during embryonic development
· visceral mass is rotated up to 180 degrees
· anus and mantle cavity are above the head (in adults)
· some of the organs that were bilateral are reduced/lost on one side of the body
o aquatic species = gills
o terrestrial species = lining of the mantle cavity functions as lung
- Polyplacophora (chitons)
o oval shaped
o unsegmented bodies
o shells divided into eight dorsal plates
o muscular foot used to grips rock substrates and creep over them
o grazers à used radulas to scrape & ingest algae
19. There are two major characteristics that distinguish Annelida from other animal phyla, being that they have segmented bodies and live in moist habitats (sea, freshwater, damp soil)
20. The phylum Annelida is divided into three classes...
- Oligochaeta
o segmented worms
o named for their relatively sparse chaetae (bristles made of chitin)
o Earthworms
· eat their way through soil and digest it in their ailementary canal à undigested material is egested as castings, which enrich the tilled soil
· cross-fertilizing hermaphrodites
Ø 2 earthworms exchange sperm, separate, store sperm
Ø clitellum (special organ) secretes mucous cocoon
Ø cocoon slides along worm’s body, picking up stored eggs and sperm
· some are asexual and reproduce through fragmentation followed by regeneration
- Polychaeta
o polychaetes = “many setae”
o marine (w/ some exceptions)
o pair of paddle/ridgelike parapodia (“almost feet”)
· function in locomotion
· have several chitinous setae
· rich blood vessel inside function as gills (w/ some exceptions)
- Hirudinea (leeches)
o majority inhabit fresh water
o land leeches move through moist vegetation
o range in size from about 1 to 30 cm
o generally feed on other invertebrates
o some are blood-sucking parasites
· feed by attaching temporarily to host
· use blade-like jaws or enzymes to get through skin to blood
· anesthetic keeps host unaware
· secrete hirudin, an anticoagulant
21. Leeches are able to feed on blood due to their special adaptations, such as their feeding “technique.” To get through their hosts’ skin, leeches are equip with either blade-like jaws or enzymes that they can secrete to get to the blood source. Leeches also secrete anesthetics to keep their hosts unaware, so that they can suck longer and get more blood. Their hirudin secretions also are an adaptation, as they prevent blood from coagulating and allow the leeches to feed longer.
22. Characteristics Distinguishing Nematoda (Roundworms) from Other Wormlike Animals
- tough cuticle coating cylindrical body
o exoskeleton periodically shed
o new one is excreted
- alimentary tract
o use the fluid in their pseudocoelom to transport nutrients
o lack a circulatory system
- move by contracting longitudinal muscles (thrashing motion)
- reproduce sexually
o sexes generally separate
o fertilization = internal
o females can lay over 100,000 eggs per day
o zygote = resistant cell, able to survive harsh conditions
- major role in decomposition/nutrient recycling
- parasitize animals or attack plant roots
23. Over 50 species of nematodes—such as pinworms and hookworms—parasitize humans. For example, Trichinella spiralis is a species of nematodes that causes trichinosis and is acquired by consuming undercooked infected meat. The worms encyst in a variety of human organs, including skeletal muscle. These worms can hijack some of their hosts’ cellular function, thus effecting gene expression and protein coding. Nematodes do have a positive effect on the environment, however. Free-living nematodes help with decomposition and nutrient recycling. Caenorhabditis elegans, a soil organism, is a model organism in developmental biology.
24. Characteristics Distinguishing Anthropods from Other Animal Phyla
- seen as most successful phylum (three reasons in italics)
- diverse
- widely distributed à represented in nearly all habitats in the biosphere
- large population
- body segmentation and jointed appendages
o segments & appendages become specialized for variety of functions
o labor division is efficient among regions
- hard exoskeleton
o body completely covered by cuticle made of protein and chitin
o very strong – offers protection
o provides points of attachment for muscles that move appendages
o relatively impermeable to water – prevent desiccation, provides support
o can be thick & inflexible or thin & flexible – ce dépend
o must be molted during growth
§ new, larger on is secreted = ecdysis
§ animal temporarily vulnerable
- well-developed sense organ
o eyes (vision)
o olfactory receptors (smell)
o antennae (touch & smell)
o generally located at anterior end à shows extensive cephalization
- open circulatory system
o hemolymph fluid propelled by heart through short arteries into sinuses (hemocoel... not a coelom) surrounding tissues & organs
o hemolymph returns to heart through valved pores
- reduced true coelom
- specific organs for gas exchange
o aquatic à gills
§ thin, feathery extensions
§ extensive surface area in contact with water
o terrestrial à specialized internal surfaces
25. Exoskeletons can be advantageous because they are very strong and both provide protection support for the body. They also offer places where muscles can anchor in order to move appendages. Furthermore, exoskeletons are useful because they prevent dessication. However, exoskeletons can also be a disadvantage because they must be molted to accommodate for the growth of the body. During molting, while a new and larger exoskeleton is secreted in ecdysis, the animal is left vulnerable.
26. The hemocoel—sinuses connected to arteries—exists in open circulatory systems. It surrounds tissues and organs and contains hemolymph fluid. The hemocoel is not a coelom; the true coelom is very reduced in most arthropods.
27. It is believed that arthropods diverged early on into four main evolutionary lineages
- Cheliceriformes (sea spiders, horseshoe crabs, scorpions, ticks, spiders)
o named is derived from chelicerae, clawlike feeding appendages that serve as pincers/fangs
o have anterior cephalothorax and posterior abdomen
o lack sensory antennae
o most have simple eyes (with a single lens)
o earliest form was eurypterids (water scorpions) = marine and freshwater predators
o modern forms include sea spiders (pycnogonids) and horseshoe crabs
o living majority = arachnids (includes scorpions, spiders, ticks, mites)
- Myriapods (centipedes and millipedes)
o terrestrial
o millipedes = class Diplopoda
§ two pairs of walking legs on each of trunk segments, formed by two fused segments
§ eat decaying leaves and plant matter
§ among the earliest land animals
o centipedes (class Chilopoda)
§ carnivores
§ head has pair of antennae & three pairs of appendages modified as mouth parts, including jawlike mandibles
§ trunk region segments all have one pair of walking legs
§ poison claws on anteriormost trunk segment
· paralyze prey
· defense
- Hexapods (insects and their wingless, six-legged relatives)
o more species-rich than all other forms of life combined
o in almost all habitats (land, water, air)
o some are able to fly
o diverse mouths
o complex organ systems
§ regionally specialized
§ Malpighian tubules = outpockets of digestive tract, removes metabolic wastes from hemolymph
§ tracheal system (respiration) = branched, chitin-lined, carries O2 from spiracles directly to cells
§ nervous system = ventral nerve cords with several segmental ganglia
· two cords meet in the head
· ganglia from several anterior segments fuse into cerebral ganglion (brain)
· structure is close to the antennae, eyes, and other sense organs
o development through metamorphosis
§ incomplete à young are smaller with different body proportions, molting occurs until adult body and size are reached
§ complete à three stages = larval, pupal, adult
o reproduction usually sexual
§ individuals have separate sexes
§ attracted by color, odor, sound
§ females store sperm in spermatheca, in some cases holding enough sperm from a single mating to last a lifetime
§ eggs laid on food source
o important natural and agricultural pollinators
o carriers for many diseases (i.e. malaria and African sleeping sickness)
- Crustaceans (crabs, lobsters, shrimps, barnacles, and many others)
o most = marine/freshwater environment
o typically have biramous (branched), specialized appendages
§ two pairs of antennae
§ at least three pairs of mouthparts, including hard mandibles
§ walking legs present on thorax
§ appendages for swimming or reproduction found on abdomen
§ able to regenerate lost appendages during molting
o gas exchange differs based on size
§ small à exchange gases across thin areas of the cuticle
§ large à gills used
o open circulatory system
§ heart pumps hemolymph into short arteries and then into sinuses that bathe the organs
§ nitrogenous wastes excreted by diffusion through thin areas of cuticle
§ glands regulate salt balance of hemolymph
o sexual reproduction
§ most species have separate sexes
§ aquatic species have several larval stages
28. Spider have three specialized features. To begin with, they are able to inject poison into their prey to immobilize it. The poison is located in glands on their chelicerae. While consuming their prey, spiders spill some of their digestive juices into the tissues. The liquid is sucked up as their meal. Spiders also carry out gas exchange by book lungs, which are stacked plates with an extensive surface area contained in an internal chamber. Lastly, spiders are able to catch flying insects in their silk webs. The production of the protein occurs in abdominal glands. The silk begins as a liquid, but solidifies as it is spun in fibers by spinnerets. Silk fibers also function as egg covers, drop lines for a rapid escape, and “gift wrapping” for nuptial gifts.
29. Insects vary greatly and are the most species rich phylum because of two main things: their ability to fly and the diversification of their mouthparts. Insect flight evolved during the Carboniferous and Permian periods and what followed was an explosion in insect variety because new adaptive zones opened. Flying also enabled insects to escape predators and find more food and mates.
Then, insect mouthparts began to diversify due to different needs (feeding on gymnosperms and Carboniferous plants). Adaptive radiation occurred.
30. Distinguishing Characteristics of Echinoderms (i.e. sea stars)
- deuterostomes
- radial cleavage à secondary radial symmetry
- development of coelom from archenteron
- formation of anus from blastopore
- water vascular system
o network of hydraulic canals
o have tube feet, branched extensions, that function in movement, feeding, gas exchange
- thin skin covering endoskeleton of hard calcareaou plates
- most are sessile (slow moving marine animals)
- many have skeletals bumps/spines that make them prickly
- sexual reproduction à gametes released by males and females into seawater
- internal & external parts radiate from center (generally as 5 spokes)
- larvae have bilateral symmetry
- adults not perfectly radial
31. Living echinoderms are divided into six classes...
- Asteroidea (sea stars)
o multiple arms radiate from central disk
§ undersides have rows of tube feet
· act like suction disks
· controlled by hydraulic & muscular action
· can grasp substrates and prey, & creep over surfaces
§ able to pull apart bivalves (prey)
o can evert stomach through mouth
o can regernerate limbs
- Ophiuroidea (brittle stars)
o distinct central disk
o long, flexible arms
o tube feet lack suckers
o move by a serpentine lashing of arms
o suspension feeders, scavengers, or predators
- Echinoidea (sea urchins and sand dollars)
o no arms
o five rows of tube feet used for locomotion
o pivoting of long spines also enables movement
o mouths may be ringed with complex jawlike structures
o either spherical or flattened and disk-shaped
- Crinoidea (sea lilies and feather stars)
o lilies attach to substratum by stalks
o feather stars crawl using long, flexible arms
o mouth directed upward (award from substrate)
o arms (for suspension feeding) circle mouth
o very conservative evolution
- Holothuroidea (sea cucumbers)
o lack spines
o very reduced endoskeleton
o elongated oral-aboral axis
o five rows of tube feet à some function as feeding tentacles (suspension or deposit feeding)
- Concentricycloidea (sea daisies)
o discovered in 1986 à only two known species
o bodies = armless, disk-shaped, five-fold symmetry
o less than a centimeter in diameter
o absorb nutrients through the membrane surrounding body
o considered to be highly derived sea stars
32. Chordata are included in a chapter on invertebrates because the phylum does include invertebrate subphyla (although it is only 2 out of many). However, they are linked with Echidnoderms, because both are bilateral deuterostomes.
33. Echidnoderms and Chordates are developmentally similar because they are both bilateral deuterostomia. They are coelomates, with radial cleavage. Also, their coeloms develop from their archenterons and their anuses form from their blastopores.
AP Biology Ch32 Objectives
Chapter 32 - An Introduction to Animal Diversity
What Is An Animal?
1. Animals are defined by 5 characteristics. They begin with, they are (1) multicellular, ingestive heterotrophs, which means that they obtained energy by ingesting organic molecules. In addition, animals do not have cell walls as their structural support. Instead, their bodies are held together by (2) extracellular structural proteins, such as collagen. Intercellular junctions such as desmosomes, tight junctions, and gap junctions also hold tissues together. Furthermore, animals have (3) nerve and muscles cells. These two unique types of cells are used for impulse conduction and movement, respectively. Additionally, animals all share a unique family of genes called the (5) Hox genes, which contain unique homeoboxes that help regulate gene expression. Last of all, animals generally (4) reproduce sexually and tend to have the diploid stage dominating their life cycle.
- In most species, a small flagellated sperm fertilizes a larger, nonmotile egg
- A zygote forms and undergoes a series of mitotic cell divisions (cleavage)
- A multicellular, hollow ball of cells (blastula) is formed
- During gastrulation, part of the embryo folds inward, forming layers of embryonic tissues that will develop into adult body parts.
- The resulting development stage is called a gastrula.
- Some animals develop directly through transient stages into adults, but others have a distinct larval stage or stages.
- A larva is a sexually immature stage that is morphologically distinct from the adult, usually eats different foods, and may live in a different habitat from the adult.
- Animal larvae eventually undergo metamorphosis, transforming the animal into an adult.
2. In animal development, gene expression must be regulated. Hox genes are families of genes that are able to help with this regulation due to the fact that they contain special homeoboxes. Homeoboxes are common modules of DNA sequences. Because animals share the unique family of Hox genes, it is believed that this gene family arose in the eukaryotic lineage that gave rise to animals. Hox genes control cell division and differentiation, producing different morphological features of animals. In sponges, they regulate the formation of channels (a primary feature of sponge morphology), while in complex animals, they regulate patterning of the anterior-posterior axis.
The Origins of Animal Diversity
3. It is believed that animals first evolved about a billion years ago based on evidence from molecular clock calculations which estimate that the ancestors of animals diverged from the ancestors of fungi as much as 1.5 billion years ago. Similar studies suggest that the common ancestor of living animals lived 1.2 billion to 800 million years ago.
4. The Cambrian explosion was significant because during that time (about 542–525 million years ago) animals underwent considerable diversification. About half of extant animal phyla arose. The first animals with hard, mineralized skeletons fossilized.
Hypotheses for the Cause
1) The new predator-prey relationships that emerged in the Cambrian generated diversity through natural selection.
a) Adaptations helped predators catch prey
b) Prey adapted to help them resist predation
2) A rise of atmospheric oxygen preceded the Cambrian explosion, which might have provided opportunities for animals with higher metabolic rates and larger body sizes to develop.
3) The evolution of the Hox complex provided the developmental flexibility that resulted in variations in morphology.
5. Major Grades of Animal Kingdom
- Based on symmetry
o Sponges lack symmetry.
o Some animals, such as sea anemones, have radial symmetry.
o Many animals have bilateral symmetry.
§ dorsal (top) and a ventral (bottom) side
§ a left and right side
§ an anterior (head) and a posterior (tail) end
§ linked with cephalization
· evolutionary trend toward the concentration of sensory equipment (on the anterior end)
· includes the development of a central nervous system concentrated in the head and extending toward the tail as a longitudinal nerve cord
- Based on embryonic germ layers
o body plans vary according to organization of tissues
o sponges lack true tissues (collection of specialized cells isolated from others)
o gastrulation causes layering
o ectoderm - covers surface of embryo, gives rise to outer covering (and sometimes the central nervous system)
o endoderm - innermost layer, lines developing digestive tube (archenteron) and gives rise to the lining of the digestive tract and its future organs (i.e. liver & lungs of vertebrates)
o mesoderm - third germ layer, lies between the endoderm and ectoderm, develops into muscles and organs between the digestive tube and the outer covering of the animal.
- Based on the presence/absence and type of coelom
o coelomates
o pseudocoelomates
o acoelomates
explained in #7
- Based on protostome/deuterostome development
o cleavage pattern
o coelom formation
o blastopore fate
6. The symmetry of an animal generally fits its lifestyle. Radial symmetry is circular like the divisions of a pie. Many radial animals are sessile or planktonic and need to meet the environment equally well from all sides. Bilateral symmetry involves dorsal/ventral and left/right sides as well as anterior/posterior ends. Animals that move actively are generally bilateral due to the fact that bilateral symmetry is linked to the nervous system, which coordinates complex movements (i.e. crawling, burrowing, flying, and swimming).
7. Coeloms form from mesoderm tissue. Animals with a true coelom are known as coelomates. Triploblastic animals with cavities formed from blastocoel rather than mesoderm tissue are called pseudocoelomates because their cavity is a “pseudocoel.” Animals that lack a coelom are known as acoelomates. They have a solid bodies without body cavities.
A body cavity has many functions. To begin with, it can help prevent internal injury by cushioning internal organs with its fluid. The noncompressible fluid can also function as a hydrostatic skeleton against which muscles can work. The presence of a cavity also enables the internal organs to grow and move independently of the outer body wall.
8. The term diploblastic refers to an animal with only 2 germ layers, such as the cnidarian. An animal with 3 germ layers is triploblastic.
Many protostomes undergo spiral cleavage, in which planes of cell division are diagonal to the vertical axis of the embryo. Certain deuterostomes undergo radial cleavage, in which the cleavage planes are parallel or perpendicular to the vertical egg axis.
Some protostomes show determinate cleavage, where the fate of each embryonic cell is determined early in development. In indeterminate cleavage, each cell in the early embryo retains the capacity to develop into a complete embryo.
During gastrulation, the archenteron can develop in 2 distinct ways. In protostomes, solid masses of mesoderm split to form the coelomic cavities, in a pattern called schizocoelous development. In deuterostomes, mesoderm buds off from the wall of the archenteron and hollows to become the coelomic cavities, in a pattern called enterocoelous development.
9. Bilaterians are divided into one of two clades: protostomes or deuterostomes. The two differ in cleavage patterns.
- Protosomes can undergo determinate cleavage (cell fates determined early on) and/or spiral cleavage (planes of cell division are diagonal to the embryo’s vertical axis).
- Deuterostomes mostly go through radial cleavage (planes are parallel/perpendicular to the vertical egg axis). They can also show indeterminate cleavage.
Their blastopores also have different fates awaiting them.
- In many protostomes, the blastopore develops into the mouth, and a second opening at the opposite end of the gastrula develops into the anus.
- In deuterostomes, the blastopore usually develops into the anus, and the mouth is derived from the secondary opening.
Lastly, the two clades differ in coelom formation
- With protostomes, solid masses of the mesoderm split to form the coelom, in a pattern called schizocoelous development.
- In deuterostomes, mesoderm buds off from the wall of the archenteron and hollows to become the coelomic cavities, in a pattern called enterocoelous development.
10. There are 5 major features of animal phylogeny that are supported by systematic analyses of morphological characters and recent molecular studies.
- All animals share a common ancestor. The kingdom is monophyletic.
- Sponges are basal animals. They exhibit a parazoan grade of organization, without tissues. Some molecular analyses suggest that sponges are paraphyletic.
- Eumetazoa is a clade of animals with true tissues.
o All animals except sponges belong to a clade of eumetazoans.
o The common ancestor of living eumetazoans acquired true tissues.
- Most animal phyla belong to the clade Bilateria, which is defined by the shared derived character of bilateral symmetry seen in the organisms
- Vertebrates and some other phyla belong to the clade Deuterostomia, whose name refers to an animal development grade as well as a clade that includes vertebrates
11. Protostomes can be categorized as ecdysozoans or lophotrochozoans. Ecdysozoans include animals such as nematodes and arthropods that secrete external skeletons. These exoskeletons are molted as the organism grows. The Lophotrochozoans may develop lophophores, which are horseshoe-shaped crowns of ciliated tentacles used for feeding. Other organisms in this taxa have a distinctive larval stage called a trochophore larva.
What Is An Animal?
1. Animals are defined by 5 characteristics. They begin with, they are (1) multicellular, ingestive heterotrophs, which means that they obtained energy by ingesting organic molecules. In addition, animals do not have cell walls as their structural support. Instead, their bodies are held together by (2) extracellular structural proteins, such as collagen. Intercellular junctions such as desmosomes, tight junctions, and gap junctions also hold tissues together. Furthermore, animals have (3) nerve and muscles cells. These two unique types of cells are used for impulse conduction and movement, respectively. Additionally, animals all share a unique family of genes called the (5) Hox genes, which contain unique homeoboxes that help regulate gene expression. Last of all, animals generally (4) reproduce sexually and tend to have the diploid stage dominating their life cycle.
- In most species, a small flagellated sperm fertilizes a larger, nonmotile egg
- A zygote forms and undergoes a series of mitotic cell divisions (cleavage)
- A multicellular, hollow ball of cells (blastula) is formed
- During gastrulation, part of the embryo folds inward, forming layers of embryonic tissues that will develop into adult body parts.
- The resulting development stage is called a gastrula.
- Some animals develop directly through transient stages into adults, but others have a distinct larval stage or stages.
- A larva is a sexually immature stage that is morphologically distinct from the adult, usually eats different foods, and may live in a different habitat from the adult.
- Animal larvae eventually undergo metamorphosis, transforming the animal into an adult.
2. In animal development, gene expression must be regulated. Hox genes are families of genes that are able to help with this regulation due to the fact that they contain special homeoboxes. Homeoboxes are common modules of DNA sequences. Because animals share the unique family of Hox genes, it is believed that this gene family arose in the eukaryotic lineage that gave rise to animals. Hox genes control cell division and differentiation, producing different morphological features of animals. In sponges, they regulate the formation of channels (a primary feature of sponge morphology), while in complex animals, they regulate patterning of the anterior-posterior axis.
The Origins of Animal Diversity
3. It is believed that animals first evolved about a billion years ago based on evidence from molecular clock calculations which estimate that the ancestors of animals diverged from the ancestors of fungi as much as 1.5 billion years ago. Similar studies suggest that the common ancestor of living animals lived 1.2 billion to 800 million years ago.
4. The Cambrian explosion was significant because during that time (about 542–525 million years ago) animals underwent considerable diversification. About half of extant animal phyla arose. The first animals with hard, mineralized skeletons fossilized.
Hypotheses for the Cause
1) The new predator-prey relationships that emerged in the Cambrian generated diversity through natural selection.
a) Adaptations helped predators catch prey
b) Prey adapted to help them resist predation
2) A rise of atmospheric oxygen preceded the Cambrian explosion, which might have provided opportunities for animals with higher metabolic rates and larger body sizes to develop.
3) The evolution of the Hox complex provided the developmental flexibility that resulted in variations in morphology.
5. Major Grades of Animal Kingdom
- Based on symmetry
o Sponges lack symmetry.
o Some animals, such as sea anemones, have radial symmetry.
o Many animals have bilateral symmetry.
§ dorsal (top) and a ventral (bottom) side
§ a left and right side
§ an anterior (head) and a posterior (tail) end
§ linked with cephalization
· evolutionary trend toward the concentration of sensory equipment (on the anterior end)
· includes the development of a central nervous system concentrated in the head and extending toward the tail as a longitudinal nerve cord
- Based on embryonic germ layers
o body plans vary according to organization of tissues
o sponges lack true tissues (collection of specialized cells isolated from others)
o gastrulation causes layering
o ectoderm - covers surface of embryo, gives rise to outer covering (and sometimes the central nervous system)
o endoderm - innermost layer, lines developing digestive tube (archenteron) and gives rise to the lining of the digestive tract and its future organs (i.e. liver & lungs of vertebrates)
o mesoderm - third germ layer, lies between the endoderm and ectoderm, develops into muscles and organs between the digestive tube and the outer covering of the animal.
- Based on the presence/absence and type of coelom
o coelomates
o pseudocoelomates
o acoelomates
explained in #7
- Based on protostome/deuterostome development
o cleavage pattern
o coelom formation
o blastopore fate
6. The symmetry of an animal generally fits its lifestyle. Radial symmetry is circular like the divisions of a pie. Many radial animals are sessile or planktonic and need to meet the environment equally well from all sides. Bilateral symmetry involves dorsal/ventral and left/right sides as well as anterior/posterior ends. Animals that move actively are generally bilateral due to the fact that bilateral symmetry is linked to the nervous system, which coordinates complex movements (i.e. crawling, burrowing, flying, and swimming).
7. Coeloms form from mesoderm tissue. Animals with a true coelom are known as coelomates. Triploblastic animals with cavities formed from blastocoel rather than mesoderm tissue are called pseudocoelomates because their cavity is a “pseudocoel.” Animals that lack a coelom are known as acoelomates. They have a solid bodies without body cavities.
A body cavity has many functions. To begin with, it can help prevent internal injury by cushioning internal organs with its fluid. The noncompressible fluid can also function as a hydrostatic skeleton against which muscles can work. The presence of a cavity also enables the internal organs to grow and move independently of the outer body wall.
8. The term diploblastic refers to an animal with only 2 germ layers, such as the cnidarian. An animal with 3 germ layers is triploblastic.
Many protostomes undergo spiral cleavage, in which planes of cell division are diagonal to the vertical axis of the embryo. Certain deuterostomes undergo radial cleavage, in which the cleavage planes are parallel or perpendicular to the vertical egg axis.
Some protostomes show determinate cleavage, where the fate of each embryonic cell is determined early in development. In indeterminate cleavage, each cell in the early embryo retains the capacity to develop into a complete embryo.
During gastrulation, the archenteron can develop in 2 distinct ways. In protostomes, solid masses of mesoderm split to form the coelomic cavities, in a pattern called schizocoelous development. In deuterostomes, mesoderm buds off from the wall of the archenteron and hollows to become the coelomic cavities, in a pattern called enterocoelous development.
9. Bilaterians are divided into one of two clades: protostomes or deuterostomes. The two differ in cleavage patterns.
- Protosomes can undergo determinate cleavage (cell fates determined early on) and/or spiral cleavage (planes of cell division are diagonal to the embryo’s vertical axis).
- Deuterostomes mostly go through radial cleavage (planes are parallel/perpendicular to the vertical egg axis). They can also show indeterminate cleavage.
Their blastopores also have different fates awaiting them.
- In many protostomes, the blastopore develops into the mouth, and a second opening at the opposite end of the gastrula develops into the anus.
- In deuterostomes, the blastopore usually develops into the anus, and the mouth is derived from the secondary opening.
Lastly, the two clades differ in coelom formation
- With protostomes, solid masses of the mesoderm split to form the coelom, in a pattern called schizocoelous development.
- In deuterostomes, mesoderm buds off from the wall of the archenteron and hollows to become the coelomic cavities, in a pattern called enterocoelous development.
10. There are 5 major features of animal phylogeny that are supported by systematic analyses of morphological characters and recent molecular studies.
- All animals share a common ancestor. The kingdom is monophyletic.
- Sponges are basal animals. They exhibit a parazoan grade of organization, without tissues. Some molecular analyses suggest that sponges are paraphyletic.
- Eumetazoa is a clade of animals with true tissues.
o All animals except sponges belong to a clade of eumetazoans.
o The common ancestor of living eumetazoans acquired true tissues.
- Most animal phyla belong to the clade Bilateria, which is defined by the shared derived character of bilateral symmetry seen in the organisms
- Vertebrates and some other phyla belong to the clade Deuterostomia, whose name refers to an animal development grade as well as a clade that includes vertebrates
11. Protostomes can be categorized as ecdysozoans or lophotrochozoans. Ecdysozoans include animals such as nematodes and arthropods that secrete external skeletons. These exoskeletons are molted as the organism grows. The Lophotrochozoans may develop lophophores, which are horseshoe-shaped crowns of ciliated tentacles used for feeding. Other organisms in this taxa have a distinctive larval stage called a trochophore larva.
AP Biology Ch35 Objectives
Chapter 35 - Plants
1. Vascular plants have three basic organs: roots, stems, and leaves. Roots are organs that anchor a vascular plant in the soil, absorb minerals and water, and store food. Stems are organs that consist of alternating nodes, points at which leaves are attached, and internodes, stem segments between nodes. Leaves are the main photosynthetic organs of most plants, although green stems are also photosynthetic. Each of these systems is interdependent of each other. Lacking chloroplasts and living in the dark, roots would starve without the sugar and other organic nutrients imported from the photosynthetic tissues of the shoot system.
2. A root is an organ that anchors a vascular plant in the soil, absorbs minerals and water, and stores food. Most eudicots and gymnosperms have a taproot system, consisting of one large vertical root (the taproot) that produces many small lateral, or branch, roots. Seedless vascular plants and most monocots, including grasses, have fibrous root systems consisting of a mat of thin roots that spread out below the soil surface. A fibrous root system is usually shallower than a taproot system. Grass roots are concentrated in the upper few centimeters of soil. As a result, grasses make excellent ground cover for preventing erosion. Sturdy, horizontal, underground stems called rhizomes anchor large monocots such as palms and bamboo. In both taproot and fibrous root systems, absorption of water and minerals occurs near the root tips, where vast numbers of tiny root hairs (extensions of individual epidermal cells on the root surface) enormously increase the surface area. Some plants have modified roots. Some arise from roots while adventitious roots arise aboveground from stems or even from leaves. Some modified roots provide additional support and anchorage. Others store water and nutrients or absorb oxygen or water from the air.
3. Modified shoots with diverse functions have evolved in many plants. These shoots include stolons, rhizomes, tubers, and bulbs. Stolons, such as the "runners" of strawberry plants, are horizontal stems that grow on the surface and enable a plant to colonize large areas asexually as plantlets form at nodes along each runner. Rhizomes, like those of ginger, are horizontal stems that grow underground. Tubers, including potatoes, are the swollen ends of rhizomes specialized for food storage. Bulbs, such as onions, are vertical, underground shoots consisting mostly of the swollen bases of leaves that store food.
4. Leaves are the main photosynthetic organs of most plants, although green stems are also photosynthetic. While leaves vary extensively in form, they generally consist of a flattened blade and a stalk, the petiole, which joins the leaf to a stem node. Grasses and other monocots lack petioles. In these plants, the base of the leaf forms a sheath that envelops the stem. Most monocots have parallel major veins that run the length of the blade, while eudicot leaves have a multibranched network of major veins.
5. Each organ of a plant has three tissue systems (dermal, vascular, and ground) that are continuous throughout the plant body. The dermal tissue is the outer covering. In nonwoody plants, it is a single layer of tightly packed cells, or epidermis, which covers and protects all young parts of the plant. The epidermis has other specialized characteristics consistent with the function of the organ it covers (i.e. (1) the root hairs are extensions of epidermal cells near the tips of the roots (2) The epidermis of leaves and most stems secretes a waxy coating, the cuticle, which helps the aerial parts of the plant retain water). In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots. Vascular tissue is involved in the transport of materials between roots and shoots. Xylem conveys water and dissolved minerals upward from roots into the shoots. Phloem transports food made in mature leaves to the roots; to nonphotosynthetic parts of the shoot system; and to sites of growth, such as developing leaves and fruits. The vascular tissue of a root or stem is called the stele. In angiosperms, the vascular tissue of the root forms a solid central vascular cylinder, while stems and leaves have vascular bundles, strands consisting of xylem and phloem. Ground tissue is tissue that is neither dermal tissue nor vascular tissue. In eudicot stems, ground tissue is divided into pith, internal to vascular tissue, and cortex, external to the vascular tissue. The functions of ground tissue include photosynthesis, storage, and support (i.e. the cortex of a eudicot stem typically consists of both fleshy storage cells and thick-walled support cells).
6. Leaves are the main photosynthetic organs of most plants, although green stems are also photosynthetic. While leaves vary extensively in form, they generally consist of a flattened blade and a stalk, the petiole, which joins the leaf to a stem node. Grasses and other monocots lack petioles. In these plants, the base of the leaf forms a sheath that envelops the stem. Most monocots have parallel major veins that run the length of the blade, while eudicot leaves have a multibranched network of major veins.
7. Each organ of a plant has three tissue systems (dermal, vascular, and ground) that are continuous throughout the plant body. The dermal tissue is the outer covering. In nonwoody plants, it is a single layer of tightly packed cells, or epidermis, which covers and protects all young parts of the plant. The epidermis has other specialized characteristics consistent with the function of the organ it covers (i.e. (1) the root hairs are extensions of epidermal cells near the tips of the roots (2) The epidermis of leaves and most stems secretes a waxy coating, the cuticle, which helps the aerial parts of the plant retain water). In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots. Vascular tissue is involved in the transport of materials between roots and shoots. Xylem conveys water and dissolved minerals upward from roots into the shoots. Phloem transports food made in mature leaves to the roots; to nonphotosynthetic parts of the shoot system; and to sites of growth, such as developing leaves and fruits. The vascular tissue of a root or stem is called the stele. In angiosperms, the vascular tissue of the root forms a solid central vascular cylinder, while stems and leaves have vascular bundles, strands consisting of xylem and phloem. Ground tissue is tissue that is neither dermal tissue nor vascular tissue. In eudicot stems, ground tissue is divided into pith, internal to vascular tissue, and cortex, external to the vascular tissue. The functions of ground tissue include photosynthesis, storage, and support (i.e. the cortex of a eudicot stem typically consists of both fleshy storage cells and thick-walled support cells).
8. The major types of differentiated plant cells are parenchyma, collenchyma, and sclerenchyma. Mature parenchyma cells have primary walls that are relatively thin and flexible, and most lack secondary walls. The protoplast of a parenchyma cell usually has a large central vacuole. Parenchyma cells are often depicted as "typical" plant cells because they generally are the least specialized, but there are exceptions (i.e. highly specialized sieve-tube members of the phloem are parenchyma cells). Parenchyma cells perform most of the metabolic functions of the plant, synthesizing and storing various organic products (i.e. photosynthesis occurs within the chloroplasts of parenchyma cells in the leaf). Some parenchyma cells in the stems and roots have colorless plastids that store starch. The fleshy tissue of most fruit is composed of parenchyma cells. Most parenchyma cells retain the ability to divide and differentiate into other cell types under special conditions, such as the repair and replacement of organs after injury to the plant. In the laboratory, it is possible to regenerate an entire plant from a single parenchyma cell. Collenchyma cells have thicker primary walls than parenchyma cells, though the walls are unevenly thickened. Grouped into strands or cylinders, collenchyma cells help support young parts of the plant shoot. Young stems and petioles often have strands of collenchyma just below the epidermis, providing support without restraining growth. Mature collenchyma cells are living and flexible and elongate with the stems and leaves they support. Sclerenchyma cells (water-conducting cells of the xylem and sugar-conducting cells of the phloem) have thick secondary walls usually strengthened by lignin and function as supporting elements of the plant. They are much more rigid than collenchyma cells. Unlike parenchyma cells, they cannot elongate. Sclerenchyma cells occur in plant regions that have stopped lengthening. Many sclerenchyma cells are dead at functional maturity, but they produce rigid secondary cells walls before the protoplast dies. In parts of the plant that are still elongating, secondary walls are deposited in a spiral or ring pattern, enabling the cell wall to stretch like a spring as the cell grows. Two types of sclerenchyma cells, fibers and sclereids, are specialized entirely for support. Fibers are long, slender, and tapered, and usually occur in groups. Sclereids are irregular in shape and are shorter than fibers (very thick, lignified secondary walls). The water-conducting elements of xylem, the tracheids and vessel elements, are elongated cells that are dead at functional maturity. The thickened cell walls remain as a nonliving conduit through which water can flow. Both tracheids and vessels have secondary walls interrupted by pits, thinner regions where only primary walls are present. Tracheids are long, thin cells with tapered ends. Because their secondary walls are hardened with lignin, tracheids function in support as well as transport. Vessel elements are generally wider, shorter, thinner walled, and less tapered than tracheids. They are aligned end to end, forming long micropipes or xylem vessels. The ends are perforated, enabling water to flow freely.
9. In the phloem, sucrose, other organic compounds, and some mineral ions move through tubes formed by chains of cells called sieve-tube members. These are alive at functional maturity, although a sieve-tube member lacks a nucleus, ribosomes, and a distinct vacuole. The end walls, the sieve plates, have pores that facilitate the flow of fluid between cells. Each sieve-tube member has a nonconducting nucleated companion cell, which is connected to the sieve-tube member by numerous plasmodesmata. The nucleus and ribosomes of the companion cell serve both that cell and the adjacent sieve-tube member. In some plants, companion cells in leaves help load sugar into the sieve-tube members, which transport the sugars to other parts of the plant.
10. Most plants demonstrate indeterminate growth, growing as long as the plant lives. In contrast, most animals and certain plant organs, such as flowers and leaves, undergo determinate growth, ceasing to grow after they reach a certain size.
11. Annual plants complete their life cycle—from germination through flowering and seed production to death—in a single year or less. Many wildflowers and important food crops, such as cereals and legumes, are annuals. The life of a biennial plant spans two years. Often, there is an intervening cold period between the vegetative growth season and the flowering season. Plants such as trees, shrubs, and some grasses that live many years are perennials. Perennials do not usually die from old age, but from an infection or some environmental trauma.
12. A plant is capable of indeterminate growth because it has perpetually embryonic tissues called meristems in its regions of growth. These cells divide to generate additional cells, some of which remain in the meristematic region, while others become specialized and are incorporated into the tissues and organs of the growing plant. Cells that remain as wellsprings of new cells in the meristem are called initials. Those that are displaced from the meristem, derivatives, continue to divide for some time until the cells they produce differentiate within developing tissues. The pattern of plant growth depends on the location of meristems. Apical meristems, located at the tips of roots and in the buds of shoots, supply cells for the plant to grow in length.
13. Primary growth enables roots to extend through the soil and shoots to increase their exposure to light and carbon dioxide. In herbaceous plants, primary growth produces almost all of the plant body. Woody plants also show secondary growth, progressive thickening of roots and shoots where primary growth has ceased. Secondary growth is produced by lateral meristems, cylinders of dividing cells that extend along the length of roots and shoots. The vascular cambium adds layers of vascular tissue called secondary xylem and phloem. The cork cambium replaces the epidermis with thicker, tougher periderm. ** In woody plants, primary growth produces young extensions of roots and shoots each growing season, while secondary growth thickens and strengthens the older parts of the plant.
17. Modern molecular techniques allow plant biologists to investigate how growth, morphogenesis, and cellular differentiation give rise to a plant. Much of this research has focused on Arabidopsis thaliana, a small weed in the mustard family. Thousands of these small plants can be cultivated in a few square meters of lab space. With a generation time of about six weeks, it is an excellent model for genetic studies.
18. Arabidopsis & Plant Development
a. Fass mutants have unusually squat cells, which follow seemingly random planes of cell division. Their roots and stems lack the ordered cell files and layers. Fass mutants develop into tiny adult plants with all their organs compressed longitudinally. The cortical microtubular organization of fass mutants is abnormal. Although the microtubules involved in chromosome movement and in cell plate deposition are normal, preprophase bands do not form prior to mitosis. In interphase cells, the cortical microtubules are randomly positioned. Therefore, the cellulose microfibrils deposited in the cell wall cannot be arranged to determine the direction of the cell's elongation. Cells with a fass mutation expand in all directions equally and divide in a haphazard arrangement, leading to stout stature and disorganized tissues.
b. Gnom mutant – In the gnom mutant of Arabidopsis , the first division is symmetrical, and the resulting ball-shaped plant lacks roots and leaves.
c. KNOTTED-1 – the protein product of the homeotic gene is important for the development of leaf morphology, including production of compound leaves. Overexpression of this gene causes the compound leaves of a tomato plant to become "supercompound."
d. GLABRA-2 – normally expressed only in hairless cells. If it is rendered dysfunctional, every root epidermal cell develops a root hair
19. Morphogenesis is the development of body form and organization. Growth is an increase in mass, resulting from cell division and cell expansion. The specialization of cells with the same set of genetic instructions to produce a diversity of cell types is called differentiation.
20. Plants growth and development are affected plane (direction) and symmetry of cell division, the orientation of cell expansion, and cortical microtubules.
- If the planes of division by a single cell and its descendents are parallel to the plane of the first cell division, a single file of cells will be produced. If the planes of cell division of the descendent cells vary at random, an unorganized clump of cells will result.
- Cell expansion in plants involves adding some organic material to their cytoplasm. 90% of the expansion, however, is accounted for by the water uptake of a large central vacuole.
- The cortical microtubular organization of fass mutants is abnormal. Although the microtubules involved in chromosome movement and in cell plate deposition are normal, preprophase bands do not form prior to mitosis. In interphase cells, the cortical microtubules are randomly positioned. Therefore, the cellulose microfibrils deposited in the cell wall cannot be arranged to determine the direction of the cell’s elongation. Cells with a fass mutation expand in all directions equally and divide in a haphazard arrangement, leading to stout stature and disorganized tissues.
21. The development of specific structures in specific locations is called pattern formation. Pattern formation depends to a large extent on positional information, signals that continuously indicate each cell’s location within an embryonic structure. Within a developing organ, each cell responds to positional information by differentiating into a particular cell type.
22. The importance of a cell’s location in its developmental fate is shown by clonal analysis of the shoot apex. In the process of shaping a rudimentary organ, patterns of cell division and cell expansion affect the differentiation of cells by placing them in specific locations relative to other cells. Thus, positional information underlies all the processes of development: growth, morphogenesis, and differentiation.
To some extent, the developmental fates of cells in the shoot apex are predictable. Clonal mapping has shown that almost all the cells derived from division of the outermost meristematic cells become part of the dermal tissue of leaves and stems. However, it is not possible to pinpoint precisely which cells of the meristem will give rise to specific tissues and organs because random changes in rates and planes of cell division can reorganize the meristem. For example, the outermost cells usually divide in a plane parallel to the surface of the shoot apex. Occasionally, an outer cell divides in a plane perpendicular to this layer, placing one daughter cell beneath the surface, among cells derived from different lineages. In plants, a cell’s developmental fate is determined not by its membership in a particular lineage but by its final position in an emerging organ.
23. The switch from a vegetative shoot tip to a floral meristem is triggered by a combination of environmental cues (i.e. day length & internal signals, like hormones). Unlike vegetative growth, which is indeterminate, the production of a flower by an apical meristem terminates primary growth of that shoot tip as the apical meristem develops into the flower’s organs. This transition is associated with the switching on of floral meristem identity genes. The protein products of these genes are transcription factors that help activate the genes required for the development of the floral meristem. Once a shoot meristem is induced to flower, positional information commits each primordium arising from the flanks of the shoot tip to develop into a specific flower organ. Organ identity genes regulate positional information and function in the development of the floral pattern.
24. In Arabidopsis, three classes of organ identity genes interact to produce the spatial pattern of floral organs. The ABC model of flower formation—which proposes that each class of organ identity genes is switched on in 2 specific whorls of the floral meristem—identifies how these genes direct the formation of four types of floral organs.
§ A genes are switched on in the two outer whorls (sepals and petals)
§ B genes are switched on in the two middle whorls (petals and stamens)
§ C genes are switched on in the two inner whorls (stamens and carpels)
Sepals arise in those parts of the floral meristems in which only A genes are active. When A and B genes are active, petals arise in those parts of the floral meristems. Stamens arise in those parts of the floral meristems in which B and C genes are active. Lastly, carpels arise in those parts of the floral meristems in which only C genes are active.
1. Vascular plants have three basic organs: roots, stems, and leaves. Roots are organs that anchor a vascular plant in the soil, absorb minerals and water, and store food. Stems are organs that consist of alternating nodes, points at which leaves are attached, and internodes, stem segments between nodes. Leaves are the main photosynthetic organs of most plants, although green stems are also photosynthetic. Each of these systems is interdependent of each other. Lacking chloroplasts and living in the dark, roots would starve without the sugar and other organic nutrients imported from the photosynthetic tissues of the shoot system.
2. A root is an organ that anchors a vascular plant in the soil, absorbs minerals and water, and stores food. Most eudicots and gymnosperms have a taproot system, consisting of one large vertical root (the taproot) that produces many small lateral, or branch, roots. Seedless vascular plants and most monocots, including grasses, have fibrous root systems consisting of a mat of thin roots that spread out below the soil surface. A fibrous root system is usually shallower than a taproot system. Grass roots are concentrated in the upper few centimeters of soil. As a result, grasses make excellent ground cover for preventing erosion. Sturdy, horizontal, underground stems called rhizomes anchor large monocots such as palms and bamboo. In both taproot and fibrous root systems, absorption of water and minerals occurs near the root tips, where vast numbers of tiny root hairs (extensions of individual epidermal cells on the root surface) enormously increase the surface area. Some plants have modified roots. Some arise from roots while adventitious roots arise aboveground from stems or even from leaves. Some modified roots provide additional support and anchorage. Others store water and nutrients or absorb oxygen or water from the air.
3. Modified shoots with diverse functions have evolved in many plants. These shoots include stolons, rhizomes, tubers, and bulbs. Stolons, such as the "runners" of strawberry plants, are horizontal stems that grow on the surface and enable a plant to colonize large areas asexually as plantlets form at nodes along each runner. Rhizomes, like those of ginger, are horizontal stems that grow underground. Tubers, including potatoes, are the swollen ends of rhizomes specialized for food storage. Bulbs, such as onions, are vertical, underground shoots consisting mostly of the swollen bases of leaves that store food.
4. Leaves are the main photosynthetic organs of most plants, although green stems are also photosynthetic. While leaves vary extensively in form, they generally consist of a flattened blade and a stalk, the petiole, which joins the leaf to a stem node. Grasses and other monocots lack petioles. In these plants, the base of the leaf forms a sheath that envelops the stem. Most monocots have parallel major veins that run the length of the blade, while eudicot leaves have a multibranched network of major veins.
5. Each organ of a plant has three tissue systems (dermal, vascular, and ground) that are continuous throughout the plant body. The dermal tissue is the outer covering. In nonwoody plants, it is a single layer of tightly packed cells, or epidermis, which covers and protects all young parts of the plant. The epidermis has other specialized characteristics consistent with the function of the organ it covers (i.e. (1) the root hairs are extensions of epidermal cells near the tips of the roots (2) The epidermis of leaves and most stems secretes a waxy coating, the cuticle, which helps the aerial parts of the plant retain water). In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots. Vascular tissue is involved in the transport of materials between roots and shoots. Xylem conveys water and dissolved minerals upward from roots into the shoots. Phloem transports food made in mature leaves to the roots; to nonphotosynthetic parts of the shoot system; and to sites of growth, such as developing leaves and fruits. The vascular tissue of a root or stem is called the stele. In angiosperms, the vascular tissue of the root forms a solid central vascular cylinder, while stems and leaves have vascular bundles, strands consisting of xylem and phloem. Ground tissue is tissue that is neither dermal tissue nor vascular tissue. In eudicot stems, ground tissue is divided into pith, internal to vascular tissue, and cortex, external to the vascular tissue. The functions of ground tissue include photosynthesis, storage, and support (i.e. the cortex of a eudicot stem typically consists of both fleshy storage cells and thick-walled support cells).
6. Leaves are the main photosynthetic organs of most plants, although green stems are also photosynthetic. While leaves vary extensively in form, they generally consist of a flattened blade and a stalk, the petiole, which joins the leaf to a stem node. Grasses and other monocots lack petioles. In these plants, the base of the leaf forms a sheath that envelops the stem. Most monocots have parallel major veins that run the length of the blade, while eudicot leaves have a multibranched network of major veins.
7. Each organ of a plant has three tissue systems (dermal, vascular, and ground) that are continuous throughout the plant body. The dermal tissue is the outer covering. In nonwoody plants, it is a single layer of tightly packed cells, or epidermis, which covers and protects all young parts of the plant. The epidermis has other specialized characteristics consistent with the function of the organ it covers (i.e. (1) the root hairs are extensions of epidermal cells near the tips of the roots (2) The epidermis of leaves and most stems secretes a waxy coating, the cuticle, which helps the aerial parts of the plant retain water). In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots. Vascular tissue is involved in the transport of materials between roots and shoots. Xylem conveys water and dissolved minerals upward from roots into the shoots. Phloem transports food made in mature leaves to the roots; to nonphotosynthetic parts of the shoot system; and to sites of growth, such as developing leaves and fruits. The vascular tissue of a root or stem is called the stele. In angiosperms, the vascular tissue of the root forms a solid central vascular cylinder, while stems and leaves have vascular bundles, strands consisting of xylem and phloem. Ground tissue is tissue that is neither dermal tissue nor vascular tissue. In eudicot stems, ground tissue is divided into pith, internal to vascular tissue, and cortex, external to the vascular tissue. The functions of ground tissue include photosynthesis, storage, and support (i.e. the cortex of a eudicot stem typically consists of both fleshy storage cells and thick-walled support cells).
8. The major types of differentiated plant cells are parenchyma, collenchyma, and sclerenchyma. Mature parenchyma cells have primary walls that are relatively thin and flexible, and most lack secondary walls. The protoplast of a parenchyma cell usually has a large central vacuole. Parenchyma cells are often depicted as "typical" plant cells because they generally are the least specialized, but there are exceptions (i.e. highly specialized sieve-tube members of the phloem are parenchyma cells). Parenchyma cells perform most of the metabolic functions of the plant, synthesizing and storing various organic products (i.e. photosynthesis occurs within the chloroplasts of parenchyma cells in the leaf). Some parenchyma cells in the stems and roots have colorless plastids that store starch. The fleshy tissue of most fruit is composed of parenchyma cells. Most parenchyma cells retain the ability to divide and differentiate into other cell types under special conditions, such as the repair and replacement of organs after injury to the plant. In the laboratory, it is possible to regenerate an entire plant from a single parenchyma cell. Collenchyma cells have thicker primary walls than parenchyma cells, though the walls are unevenly thickened. Grouped into strands or cylinders, collenchyma cells help support young parts of the plant shoot. Young stems and petioles often have strands of collenchyma just below the epidermis, providing support without restraining growth. Mature collenchyma cells are living and flexible and elongate with the stems and leaves they support. Sclerenchyma cells (water-conducting cells of the xylem and sugar-conducting cells of the phloem) have thick secondary walls usually strengthened by lignin and function as supporting elements of the plant. They are much more rigid than collenchyma cells. Unlike parenchyma cells, they cannot elongate. Sclerenchyma cells occur in plant regions that have stopped lengthening. Many sclerenchyma cells are dead at functional maturity, but they produce rigid secondary cells walls before the protoplast dies. In parts of the plant that are still elongating, secondary walls are deposited in a spiral or ring pattern, enabling the cell wall to stretch like a spring as the cell grows. Two types of sclerenchyma cells, fibers and sclereids, are specialized entirely for support. Fibers are long, slender, and tapered, and usually occur in groups. Sclereids are irregular in shape and are shorter than fibers (very thick, lignified secondary walls). The water-conducting elements of xylem, the tracheids and vessel elements, are elongated cells that are dead at functional maturity. The thickened cell walls remain as a nonliving conduit through which water can flow. Both tracheids and vessels have secondary walls interrupted by pits, thinner regions where only primary walls are present. Tracheids are long, thin cells with tapered ends. Because their secondary walls are hardened with lignin, tracheids function in support as well as transport. Vessel elements are generally wider, shorter, thinner walled, and less tapered than tracheids. They are aligned end to end, forming long micropipes or xylem vessels. The ends are perforated, enabling water to flow freely.
9. In the phloem, sucrose, other organic compounds, and some mineral ions move through tubes formed by chains of cells called sieve-tube members. These are alive at functional maturity, although a sieve-tube member lacks a nucleus, ribosomes, and a distinct vacuole. The end walls, the sieve plates, have pores that facilitate the flow of fluid between cells. Each sieve-tube member has a nonconducting nucleated companion cell, which is connected to the sieve-tube member by numerous plasmodesmata. The nucleus and ribosomes of the companion cell serve both that cell and the adjacent sieve-tube member. In some plants, companion cells in leaves help load sugar into the sieve-tube members, which transport the sugars to other parts of the plant.
10. Most plants demonstrate indeterminate growth, growing as long as the plant lives. In contrast, most animals and certain plant organs, such as flowers and leaves, undergo determinate growth, ceasing to grow after they reach a certain size.
11. Annual plants complete their life cycle—from germination through flowering and seed production to death—in a single year or less. Many wildflowers and important food crops, such as cereals and legumes, are annuals. The life of a biennial plant spans two years. Often, there is an intervening cold period between the vegetative growth season and the flowering season. Plants such as trees, shrubs, and some grasses that live many years are perennials. Perennials do not usually die from old age, but from an infection or some environmental trauma.
12. A plant is capable of indeterminate growth because it has perpetually embryonic tissues called meristems in its regions of growth. These cells divide to generate additional cells, some of which remain in the meristematic region, while others become specialized and are incorporated into the tissues and organs of the growing plant. Cells that remain as wellsprings of new cells in the meristem are called initials. Those that are displaced from the meristem, derivatives, continue to divide for some time until the cells they produce differentiate within developing tissues. The pattern of plant growth depends on the location of meristems. Apical meristems, located at the tips of roots and in the buds of shoots, supply cells for the plant to grow in length.
13. Primary growth enables roots to extend through the soil and shoots to increase their exposure to light and carbon dioxide. In herbaceous plants, primary growth produces almost all of the plant body. Woody plants also show secondary growth, progressive thickening of roots and shoots where primary growth has ceased. Secondary growth is produced by lateral meristems, cylinders of dividing cells that extend along the length of roots and shoots. The vascular cambium adds layers of vascular tissue called secondary xylem and phloem. The cork cambium replaces the epidermis with thicker, tougher periderm. ** In woody plants, primary growth produces young extensions of roots and shoots each growing season, while secondary growth thickens and strengthens the older parts of the plant.
17. Modern molecular techniques allow plant biologists to investigate how growth, morphogenesis, and cellular differentiation give rise to a plant. Much of this research has focused on Arabidopsis thaliana, a small weed in the mustard family. Thousands of these small plants can be cultivated in a few square meters of lab space. With a generation time of about six weeks, it is an excellent model for genetic studies.
18. Arabidopsis & Plant Development
a. Fass mutants have unusually squat cells, which follow seemingly random planes of cell division. Their roots and stems lack the ordered cell files and layers. Fass mutants develop into tiny adult plants with all their organs compressed longitudinally. The cortical microtubular organization of fass mutants is abnormal. Although the microtubules involved in chromosome movement and in cell plate deposition are normal, preprophase bands do not form prior to mitosis. In interphase cells, the cortical microtubules are randomly positioned. Therefore, the cellulose microfibrils deposited in the cell wall cannot be arranged to determine the direction of the cell's elongation. Cells with a fass mutation expand in all directions equally and divide in a haphazard arrangement, leading to stout stature and disorganized tissues.
b. Gnom mutant – In the gnom mutant of Arabidopsis , the first division is symmetrical, and the resulting ball-shaped plant lacks roots and leaves.
c. KNOTTED-1 – the protein product of the homeotic gene is important for the development of leaf morphology, including production of compound leaves. Overexpression of this gene causes the compound leaves of a tomato plant to become "supercompound."
d. GLABRA-2 – normally expressed only in hairless cells. If it is rendered dysfunctional, every root epidermal cell develops a root hair
19. Morphogenesis is the development of body form and organization. Growth is an increase in mass, resulting from cell division and cell expansion. The specialization of cells with the same set of genetic instructions to produce a diversity of cell types is called differentiation.
20. Plants growth and development are affected plane (direction) and symmetry of cell division, the orientation of cell expansion, and cortical microtubules.
- If the planes of division by a single cell and its descendents are parallel to the plane of the first cell division, a single file of cells will be produced. If the planes of cell division of the descendent cells vary at random, an unorganized clump of cells will result.
- Cell expansion in plants involves adding some organic material to their cytoplasm. 90% of the expansion, however, is accounted for by the water uptake of a large central vacuole.
- The cortical microtubular organization of fass mutants is abnormal. Although the microtubules involved in chromosome movement and in cell plate deposition are normal, preprophase bands do not form prior to mitosis. In interphase cells, the cortical microtubules are randomly positioned. Therefore, the cellulose microfibrils deposited in the cell wall cannot be arranged to determine the direction of the cell’s elongation. Cells with a fass mutation expand in all directions equally and divide in a haphazard arrangement, leading to stout stature and disorganized tissues.
21. The development of specific structures in specific locations is called pattern formation. Pattern formation depends to a large extent on positional information, signals that continuously indicate each cell’s location within an embryonic structure. Within a developing organ, each cell responds to positional information by differentiating into a particular cell type.
22. The importance of a cell’s location in its developmental fate is shown by clonal analysis of the shoot apex. In the process of shaping a rudimentary organ, patterns of cell division and cell expansion affect the differentiation of cells by placing them in specific locations relative to other cells. Thus, positional information underlies all the processes of development: growth, morphogenesis, and differentiation.
To some extent, the developmental fates of cells in the shoot apex are predictable. Clonal mapping has shown that almost all the cells derived from division of the outermost meristematic cells become part of the dermal tissue of leaves and stems. However, it is not possible to pinpoint precisely which cells of the meristem will give rise to specific tissues and organs because random changes in rates and planes of cell division can reorganize the meristem. For example, the outermost cells usually divide in a plane parallel to the surface of the shoot apex. Occasionally, an outer cell divides in a plane perpendicular to this layer, placing one daughter cell beneath the surface, among cells derived from different lineages. In plants, a cell’s developmental fate is determined not by its membership in a particular lineage but by its final position in an emerging organ.
23. The switch from a vegetative shoot tip to a floral meristem is triggered by a combination of environmental cues (i.e. day length & internal signals, like hormones). Unlike vegetative growth, which is indeterminate, the production of a flower by an apical meristem terminates primary growth of that shoot tip as the apical meristem develops into the flower’s organs. This transition is associated with the switching on of floral meristem identity genes. The protein products of these genes are transcription factors that help activate the genes required for the development of the floral meristem. Once a shoot meristem is induced to flower, positional information commits each primordium arising from the flanks of the shoot tip to develop into a specific flower organ. Organ identity genes regulate positional information and function in the development of the floral pattern.
24. In Arabidopsis, three classes of organ identity genes interact to produce the spatial pattern of floral organs. The ABC model of flower formation—which proposes that each class of organ identity genes is switched on in 2 specific whorls of the floral meristem—identifies how these genes direct the formation of four types of floral organs.
§ A genes are switched on in the two outer whorls (sepals and petals)
§ B genes are switched on in the two middle whorls (petals and stamens)
§ C genes are switched on in the two inner whorls (stamens and carpels)
Sepals arise in those parts of the floral meristems in which only A genes are active. When A and B genes are active, petals arise in those parts of the floral meristems. Stamens arise in those parts of the floral meristems in which B and C genes are active. Lastly, carpels arise in those parts of the floral meristems in which only C genes are active.
AP Biology Ch30 Objectives
Chapter 30
Plant Diversity II – Evolution of Seed Plants
1. The terrestrial adaptations that contributed to the success of seed plants include: the seed, the reduction of the gametophyte generation, heterospory, ovules, and pollen.
2. The size of the gametophytes of bryophytes is tiny, but still visible to the naked eye, whereas gametophytes of seed plants are microscopically small. When considering the independence of gametophytes, the gametophytes of seed plants rely on obtaining nutrients from their parents, while the free-living gametophytes of seedless vascular plants fend for themselves.
3. The ovule of a seed plant consists of the megasporangium, megaspores which develop the female gametophyte, and integuments. The female gametophyte is retained within the sporophyte ovule. The transfer of pollen to the vicinity of the ovule is called pollination. Also, the ovule is the site where sperm is delivered in the female gametophyte through a pollen tube. The ovule is what develops into the seed, consisting of the embryo and its food supply within a protective coat derived from the integuments
4. The male gametophytes of bryophytes vs that of seed plants... [unanswered]
5. Pollen grains are an important adaptation for successful reproduction on land because it allows the male gametophytes to travel long distances. The sperm of seed plants lack flagella and do not require a film of water, as they rely on the pollen tube to reach the egg cell of the female gametophyte within the ovule. Its tough coat, which contains sporopollenin, makes it easier to be carried by the wind or animals to its destination: the ovule. Also, they contributed to diversity and variation, aiding in successful reproduction.
6. A seed can be said to include contributions from three distinct generations because ???
7. When a sperm fertilizes an egg of a seed plant, the zygote forms and develops into a sporophyte embryo. The ovule develops into a seed, consisting of the embryo and its food supply within a protective coat derived from the integuments. The evolution of the seed enabled plants to resist harsh environments and disperse offspring more widely. For bryophytes and seedless vascular plants, single-celled spores are the only protective stage in the life cycle. Moss spores can survive even if the local environment is too cold, too hot, or too dry for the moss plants themselves to survive. Because of their tiny size, the spores themselves can be dispersed in a dormant state to a new area.
8. Climatic changes with the formation of the supercontinent Pangaea favored the spread of gymnosperms because the air became warmer and drier. This type of climate allowed many organisms, including gymnosperms, to thrive, while it caused others to disappear completely.
9. Gymnosperms phylums are as follows...
v Phylum Ginkgophyta: consists of only a single extant species, Ginkgo biloba; has fanlike leaves that turn gold before falling off during autumn; coats of seeds produced by female plants produce a repulsive odor as they decay
v Phylum Cycadophyta: large cones and palmlike leaves; 130 species of survivng cycads today; flourished in the Mesozoic era
v Phylum Gnetophyta: 3 different genera; Weltwitschia plants, from deserts in southwestern Africa, have straplike leaves that are among the largest known leaves; Gentum species are tropical trees or vines; Ephedra (Mormon tea) is a shrub of the American deserts
v Phylum Coniferophyta: largest gymnosperm phylum; term conifer comes from the reproductive structure, the cone, which is a cluster of scalelike sporophylls; only about 600 species of conifers; a few species dominate vast forested regions in the Northern Hemisphere where the growing season is short; Most conifers are evergreen, retaining their leaves and photosynthesizing throughout the year; needle-shaped leaves of some conifers are adapted for dry conditions.
10. During the gametophyte generation, male and female gametophytes develop from different types of spores produced by separate cones: small pollen cones and large ovulate cones. During the sporophyte generation, each cone produces microspore mother cells that undergo meiosis to produce haploid microspores. Each microspore then develops into a pollen grain containing a male gametophyte. Ovulate cones produce megaspore mother cells that undergo meiosis to produce four haploid cells, one of which will develop into a megaspore. Surviving megaspores develop into female gametophytes, which are retained within the sporangia. Two or three archegonia, each with an egg, develop within the gametophyte. During pollination, windblown pollen falls on the ovulate cone and grows into the ovule through the micropyle, followed by fertilization. The pine embryo, the new sporophyte, has a rudimentary root and several embryonic leaves. The female gametophyte surrounds and nourishes the embryo. The ovule develops into a pine seed, which consists of an embryo (new sporophyte), its food supply (derived from gametophyte tissue), and a seed coat derived from the integuments of the parent tree (parent sporophyte). It takes three years from the appearance of young cones on a pine tree to the formation of mature seeds.
11. Sepal: modified leaves that are usually green and enclose the flower before it opens; sterile floral partPetal: lie inside the ring of sepals; sterile floral part; not directly involved in reproductionStamen: male reproductive organs; sporophylls that produce microspores that will give rise to pollen grains containing male gametophytesCarpel: female sporophylls that produce megaspores and their products, female gametophytesFilament: stalk of the stamen; pollen is producedAnther: terminal sac of stamen; pollen is producedStigma: tip of the carpal; sticky; receives pollenStyle: leads to ovary at base of carpalOvary: at base of carpal; protects ovulesOvule: protected within ovary; female reproduction
12. Fruits usually consist of a mature ovary. As seeds develop from ovules after fertilization, the wall of the ovary thickens to form the fruit. Fruits protect dormant seeds and aid in their dispersal. Fruits are adapted to disperse seeds because winged seeds may function as kites or propellers to assist wind dispersal. Also, coconuts are specialized for water dispersal. Some fruits are modified as burrs that cling to animal fur. Many fruits are edible, nutritious, sweet tasting, and colorful. These fruits rely on animals to eat the fruit and deposit the seeds, along with a supply of fertilizer, some distance from the parent plant.
13. A cereal grain is a fruit rather than a seed because the grains have dry pericarps that adhere to the seed coat of the seed.
14. Generalized Life Cycle of Angiosperm
Angiosperms have more refined versions of the alternation of generations common to all plants. The reasons behind this refinement is that angiosperms are heterosporous, and produce microspores that form male gametophytes and megaspores that form female gametophytes. The male gametophytes are found inside of pollen grains which are themselves found within the anthers of stamens. The female gametophyte—the embryo sad—is found within the ovule, which develops in the ovary.
Life Cycle
v Mature flower forms on sporophyte plants and culminates in a germinating seed
v Microspore mother cells (inside of the microsporangia, which are themselves found in anthers) produce microspores via meiosis
v Microspores form pollen grains, or immature male gametophytes
v Megaspore mother cells in ovule produce four megaspores by meiosis
v One megaspore survives to form female gametophyte, the embryo sac
v Pollen released from the anther is carried to the sticky stigma of the carpel
v Cross pollination occurs
v Pollen grain germinates into mature male gametophyte
v Pollen tube penetrates micropyle, a pore in the integuments of the ovule
v Two sperm discharged in double fertilization à One fertilized egg (forming diploid zygote), other fuses with 2 polar nuclei in the central cell of the embryo sac to form the triploid endosperm nucleus
v Zygote develops into embryo with rudimentary root and 1 or 2 seed leaves, called cotyledons
v Seed germinates, embryo becomes mature sporophyte
15. The generative cell—one of the haploid cells found in a pollen grain—divides to form two sperm as well as a tube cell. The tube cell produces a pollen tube.
16. Double fertilization, a process unique to angiosperms, occurs when two sperm are released into the female gametophyte. One sperm is used to fertilize the egg and form a diploid zygote while the other fuses with two polar nuclei in the central cell of the embryo sac to form the triploid endosperm nucleus. A special type of double fertilization evolved in gymnosperms of the phylum Gnetophyta. In this process, two embryos form. It is hypothesized that double fertilization synchronizes the development of food storage in the seed with development of the embryo. It may also prevent flowers from wasting nutrients on infertile ovules.
17. The Archaefructus is significant because 125-million-year-old fossils of the species Archaefructus liaoningensis and Archaefructus sinensis were discovered in China in the late 1990s which displayed both derived and primitive traits. The latter has both anthers and seeds inside its closed carpels, but lacks petals or sepals. It is consider a “proto-angiosperm” and its form suggests that the ancestors of flowering plants were herbaceous rather than woody. It was found along with fish fossils and may be aquatic, which has lead to suggestions from some paleobotanists that angiosperms originated as aquatic plants. Others dispute this, pointing out that aquatic angiosperms tend to evolve simpler flowers such as the “primitive” flowers of Archaefructus.
18. The Amborella is a basal angiosperm lacking vessels normally found in more derived angiosperms.
It is significant because...
19. Flowering plants were once split into 2 divisions: monocots and dicots. These categories are based upon their number of cotyledons or seed leaves. Recent research has shown, however, that while monocots form a clade, dicots are not monophyletic. Thus, plants that were once called “dicots” are now grouped into the clade “eudicots.” Eudicots, which make up about two-thirds of existing angiosperms—have pollen grains with three openings and floral parts in multiples of four or five, as well as vascular bundles arranged as a ring. A plant in this clade will also have a taproot, two cotyledons, and netlike venation. On the other hand, monocots have parallel venation, scattered vascular bundles, and a fibrous root systems. They only one cotyledon and contain pollen grains with a single opening, and floral parts in multiples of three.
20. Since their colonization of land, animals have influenced the evolution of terrestrial plants and vice versa. Animals and plants can act as each others’ selective agents. For example, since animals can easily consume plant reproductive units, natural selection favors plants that kept their spores and gametophytes above the ground. Then, flying insects helped plants disperse pollen and seeds. Animals benefited from plants because they could consume the fruits, nectar, and seeds. Then, pollinator-plant relationships helped increase animal and angiosperms diversity. Flower color, fragrance, and structures evolved to attract pollinators. The linked adaptations that occurred between plants and animals which involved reciprocal genetic modifications were called coevolution.
Examples: Grassland expansion increased diversity of grazing animals
Madagascan orchid can only be pollinated by special moth species due to evolution of nectary in former and proboscis in latter.
21. There are size angiosperms that are key in the diet of the human species, namely wheat, rice, maize, potatoes, cassava, and sweet potatoes. These plants yield 80% of all the calories consumed by men (and women... and children).
22. Plant diversity is currently threatened by the human population, whose exponential rate of growth has created an unprecedented demand for space and natural resources. This is a problem because plant diversity is not a renewable resource (although plants themselves are). In the tropics, plant diversity is especially threatened by the practice of slashing-and-burning forests to clear them for agricultural uses, which has caused the disappearance of thousands of plant species, as well as the animals that depend on them.
Plant Diversity II – Evolution of Seed Plants
1. The terrestrial adaptations that contributed to the success of seed plants include: the seed, the reduction of the gametophyte generation, heterospory, ovules, and pollen.
2. The size of the gametophytes of bryophytes is tiny, but still visible to the naked eye, whereas gametophytes of seed plants are microscopically small. When considering the independence of gametophytes, the gametophytes of seed plants rely on obtaining nutrients from their parents, while the free-living gametophytes of seedless vascular plants fend for themselves.
3. The ovule of a seed plant consists of the megasporangium, megaspores which develop the female gametophyte, and integuments. The female gametophyte is retained within the sporophyte ovule. The transfer of pollen to the vicinity of the ovule is called pollination. Also, the ovule is the site where sperm is delivered in the female gametophyte through a pollen tube. The ovule is what develops into the seed, consisting of the embryo and its food supply within a protective coat derived from the integuments
4. The male gametophytes of bryophytes vs that of seed plants... [unanswered]
5. Pollen grains are an important adaptation for successful reproduction on land because it allows the male gametophytes to travel long distances. The sperm of seed plants lack flagella and do not require a film of water, as they rely on the pollen tube to reach the egg cell of the female gametophyte within the ovule. Its tough coat, which contains sporopollenin, makes it easier to be carried by the wind or animals to its destination: the ovule. Also, they contributed to diversity and variation, aiding in successful reproduction.
6. A seed can be said to include contributions from three distinct generations because ???
7. When a sperm fertilizes an egg of a seed plant, the zygote forms and develops into a sporophyte embryo. The ovule develops into a seed, consisting of the embryo and its food supply within a protective coat derived from the integuments. The evolution of the seed enabled plants to resist harsh environments and disperse offspring more widely. For bryophytes and seedless vascular plants, single-celled spores are the only protective stage in the life cycle. Moss spores can survive even if the local environment is too cold, too hot, or too dry for the moss plants themselves to survive. Because of their tiny size, the spores themselves can be dispersed in a dormant state to a new area.
8. Climatic changes with the formation of the supercontinent Pangaea favored the spread of gymnosperms because the air became warmer and drier. This type of climate allowed many organisms, including gymnosperms, to thrive, while it caused others to disappear completely.
9. Gymnosperms phylums are as follows...
v Phylum Ginkgophyta: consists of only a single extant species, Ginkgo biloba; has fanlike leaves that turn gold before falling off during autumn; coats of seeds produced by female plants produce a repulsive odor as they decay
v Phylum Cycadophyta: large cones and palmlike leaves; 130 species of survivng cycads today; flourished in the Mesozoic era
v Phylum Gnetophyta: 3 different genera; Weltwitschia plants, from deserts in southwestern Africa, have straplike leaves that are among the largest known leaves; Gentum species are tropical trees or vines; Ephedra (Mormon tea) is a shrub of the American deserts
v Phylum Coniferophyta: largest gymnosperm phylum; term conifer comes from the reproductive structure, the cone, which is a cluster of scalelike sporophylls; only about 600 species of conifers; a few species dominate vast forested regions in the Northern Hemisphere where the growing season is short; Most conifers are evergreen, retaining their leaves and photosynthesizing throughout the year; needle-shaped leaves of some conifers are adapted for dry conditions.
10. During the gametophyte generation, male and female gametophytes develop from different types of spores produced by separate cones: small pollen cones and large ovulate cones. During the sporophyte generation, each cone produces microspore mother cells that undergo meiosis to produce haploid microspores. Each microspore then develops into a pollen grain containing a male gametophyte. Ovulate cones produce megaspore mother cells that undergo meiosis to produce four haploid cells, one of which will develop into a megaspore. Surviving megaspores develop into female gametophytes, which are retained within the sporangia. Two or three archegonia, each with an egg, develop within the gametophyte. During pollination, windblown pollen falls on the ovulate cone and grows into the ovule through the micropyle, followed by fertilization. The pine embryo, the new sporophyte, has a rudimentary root and several embryonic leaves. The female gametophyte surrounds and nourishes the embryo. The ovule develops into a pine seed, which consists of an embryo (new sporophyte), its food supply (derived from gametophyte tissue), and a seed coat derived from the integuments of the parent tree (parent sporophyte). It takes three years from the appearance of young cones on a pine tree to the formation of mature seeds.
11. Sepal: modified leaves that are usually green and enclose the flower before it opens; sterile floral partPetal: lie inside the ring of sepals; sterile floral part; not directly involved in reproductionStamen: male reproductive organs; sporophylls that produce microspores that will give rise to pollen grains containing male gametophytesCarpel: female sporophylls that produce megaspores and their products, female gametophytesFilament: stalk of the stamen; pollen is producedAnther: terminal sac of stamen; pollen is producedStigma: tip of the carpal; sticky; receives pollenStyle: leads to ovary at base of carpalOvary: at base of carpal; protects ovulesOvule: protected within ovary; female reproduction
12. Fruits usually consist of a mature ovary. As seeds develop from ovules after fertilization, the wall of the ovary thickens to form the fruit. Fruits protect dormant seeds and aid in their dispersal. Fruits are adapted to disperse seeds because winged seeds may function as kites or propellers to assist wind dispersal. Also, coconuts are specialized for water dispersal. Some fruits are modified as burrs that cling to animal fur. Many fruits are edible, nutritious, sweet tasting, and colorful. These fruits rely on animals to eat the fruit and deposit the seeds, along with a supply of fertilizer, some distance from the parent plant.
13. A cereal grain is a fruit rather than a seed because the grains have dry pericarps that adhere to the seed coat of the seed.
14. Generalized Life Cycle of Angiosperm
Angiosperms have more refined versions of the alternation of generations common to all plants. The reasons behind this refinement is that angiosperms are heterosporous, and produce microspores that form male gametophytes and megaspores that form female gametophytes. The male gametophytes are found inside of pollen grains which are themselves found within the anthers of stamens. The female gametophyte—the embryo sad—is found within the ovule, which develops in the ovary.
Life Cycle
v Mature flower forms on sporophyte plants and culminates in a germinating seed
v Microspore mother cells (inside of the microsporangia, which are themselves found in anthers) produce microspores via meiosis
v Microspores form pollen grains, or immature male gametophytes
v Megaspore mother cells in ovule produce four megaspores by meiosis
v One megaspore survives to form female gametophyte, the embryo sac
v Pollen released from the anther is carried to the sticky stigma of the carpel
v Cross pollination occurs
v Pollen grain germinates into mature male gametophyte
v Pollen tube penetrates micropyle, a pore in the integuments of the ovule
v Two sperm discharged in double fertilization à One fertilized egg (forming diploid zygote), other fuses with 2 polar nuclei in the central cell of the embryo sac to form the triploid endosperm nucleus
v Zygote develops into embryo with rudimentary root and 1 or 2 seed leaves, called cotyledons
v Seed germinates, embryo becomes mature sporophyte
15. The generative cell—one of the haploid cells found in a pollen grain—divides to form two sperm as well as a tube cell. The tube cell produces a pollen tube.
16. Double fertilization, a process unique to angiosperms, occurs when two sperm are released into the female gametophyte. One sperm is used to fertilize the egg and form a diploid zygote while the other fuses with two polar nuclei in the central cell of the embryo sac to form the triploid endosperm nucleus. A special type of double fertilization evolved in gymnosperms of the phylum Gnetophyta. In this process, two embryos form. It is hypothesized that double fertilization synchronizes the development of food storage in the seed with development of the embryo. It may also prevent flowers from wasting nutrients on infertile ovules.
17. The Archaefructus is significant because 125-million-year-old fossils of the species Archaefructus liaoningensis and Archaefructus sinensis were discovered in China in the late 1990s which displayed both derived and primitive traits. The latter has both anthers and seeds inside its closed carpels, but lacks petals or sepals. It is consider a “proto-angiosperm” and its form suggests that the ancestors of flowering plants were herbaceous rather than woody. It was found along with fish fossils and may be aquatic, which has lead to suggestions from some paleobotanists that angiosperms originated as aquatic plants. Others dispute this, pointing out that aquatic angiosperms tend to evolve simpler flowers such as the “primitive” flowers of Archaefructus.
18. The Amborella is a basal angiosperm lacking vessels normally found in more derived angiosperms.
It is significant because...
19. Flowering plants were once split into 2 divisions: monocots and dicots. These categories are based upon their number of cotyledons or seed leaves. Recent research has shown, however, that while monocots form a clade, dicots are not monophyletic. Thus, plants that were once called “dicots” are now grouped into the clade “eudicots.” Eudicots, which make up about two-thirds of existing angiosperms—have pollen grains with three openings and floral parts in multiples of four or five, as well as vascular bundles arranged as a ring. A plant in this clade will also have a taproot, two cotyledons, and netlike venation. On the other hand, monocots have parallel venation, scattered vascular bundles, and a fibrous root systems. They only one cotyledon and contain pollen grains with a single opening, and floral parts in multiples of three.
20. Since their colonization of land, animals have influenced the evolution of terrestrial plants and vice versa. Animals and plants can act as each others’ selective agents. For example, since animals can easily consume plant reproductive units, natural selection favors plants that kept their spores and gametophytes above the ground. Then, flying insects helped plants disperse pollen and seeds. Animals benefited from plants because they could consume the fruits, nectar, and seeds. Then, pollinator-plant relationships helped increase animal and angiosperms diversity. Flower color, fragrance, and structures evolved to attract pollinators. The linked adaptations that occurred between plants and animals which involved reciprocal genetic modifications were called coevolution.
Examples: Grassland expansion increased diversity of grazing animals
Madagascan orchid can only be pollinated by special moth species due to evolution of nectary in former and proboscis in latter.
21. There are size angiosperms that are key in the diet of the human species, namely wheat, rice, maize, potatoes, cassava, and sweet potatoes. These plants yield 80% of all the calories consumed by men (and women... and children).
22. Plant diversity is currently threatened by the human population, whose exponential rate of growth has created an unprecedented demand for space and natural resources. This is a problem because plant diversity is not a renewable resource (although plants themselves are). In the tropics, plant diversity is especially threatened by the practice of slashing-and-burning forests to clear them for agricultural uses, which has caused the disappearance of thousands of plant species, as well as the animals that depend on them.
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