Test 2 Study Guide - March 2, 2016
Test 2 Study Guide - March 2, 2016 BIO 1144
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This 11 page Study Guide was uploaded by Grey Garris on Sunday February 28, 2016. The Study Guide belongs to BIO 1144 at Mississippi State University taught by Dr. Williamson in Spring 2016. Since its upload, it has received 160 views. For similar materials see Biology II in Biology at Mississippi State University.
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Date Created: 02/28/16
1 BIO 1144 Bio II with Dr. Williamson Angiosperms ● Monocots vs. Dicots ○ Angiosperms have two major types: Monocots and Dicots. Both have distinct differences at multiple stages of their life cycles. ○ Monocots (Grasses, Palms, etc.) ■ Have one seed leaf. When they grow from the ground they have a single leaf that grows first. ■ They have 3 parts to their flowers. ■ The veins in their leaves are straight and parallel from the shoot end to the leaf tip. ■ The vascular bundles (channels for air) in their stems are scattered at irregular intervals throughout the body. ■ Their roots branch off in multiple directions from the instant the shoot is in the ground. This is called a Fibrous root system. ■ They only exhibit Primary Growth, which is the stem growing upwards and the roots growing downwards. ■ Their pollen grains have only one fold/pore/slit in them. ○ Dicots (Roses, Sunflowers, etc.) ■ They have two seed leaves. ■ They have 4 or 5 parts to their flowers. ■ The veins in their leaves are branching and go outward in a wide pattern called a “net.” ■ The vascular bundles are set in rings. ■ Their roots branch from a single downward reaching root called the “taproot.” ■ They exhibit Primary Growth as well as Secondary Growth, which is the thickening of the stem and roots as well as the upward/downward growth. ■ Their pollen grains have three folds/pores/slits. ● Specialized Plant Cells ○ Parenchyma ■ Least specialized of the cells in plants. They have thin, flexible cell walls and remain alive into their mature stage. They act as enablers for the metabolic functions of the plant. They usually have one large vacuole (water storage organelle). Many Parenchyma can actually change into other specialized cells given the proper conditions such as damage repair. ○ Collenchyma ■ They have thicker cell walls that can be unevenly thick and are still living at maturity. They act as support for many plants. ○ Sclerenchyma ■ They have thick cell walls and are dead when they reach maturity. They cannot grow in length so they only exist in the parts of the plant that have stopped growing in that direction. ● Fibers long, thin with a generally normal cell wall. Ex: Hemp. ● Sclerids short cells with irregular shapes. Ex: Seed shells. ○ Xylem ■ They have thick cell walls and are usually uneven but in a curling pattern to allow stretching. They are dead when they reach maturity. They help with water and mineral movement. ● Tracheids long, thin cells connected to one another by “pits.” They are found in all vascular plants. 2 ● Vessel Elements shorter than Tracheids and have a hole in their cell wall ends. These are only in angiosperms ■ Phloem ● They transport sugars and other organic compounds. They are living at maturity but may lack organelles and a nucleus. Each end is connected to the next via SievePlates, which are highly porous end caps. ○ Sieve Tube Elements the channel for sucrose to move through the plant. ○ Companion Cells cells that assist the sieve tube element and help with dispersal of sucrose. ● Plant Tissues Plants have three main types of tissues: Dermal, Ground, and Vascular. ○ Dermal Tissue The skin of the plant. It is usually only one layer of cells and mostly composed of Parenchyma cells. Its function is to protect the plant. ○ Ground Tissue This is what the majority of the plant is actually comprised of. It is mostly Parenchyma cells but has Collenchyma and Sclerenchyma cells dispersed throughout as well. It functions for photosynthesis, material storage and the structural support of the plant. ○ Vascular Tissue This is the Xylem and Phloem tissue, which is specifically for the transport of water and minerals. ● Plant Growth Plants have indeterminate growth, which means that they have tissues which constantly regenerate despite the removal of others. The cells in these tissues are undifferentiated, which means that they can become any other type of cell. ○ Meristems Meristems are the very tips of branching parts from a plant. There are two different forms: Apical and Lateral. ■ Apical Meristems These are the tips of roots and shoots (the part above the ground) and allow the plant to grow in length, which is called Primary Growth. This kind of growth occurs in Monocots and Dicots alike. ● Primary Growth in Roots ○ Root Cap The covering over the very tip of the Meristem. The Cap has special cells called Columella Cells that register gravity and allow roots to extend downward. This cap is derived from the Root Apical Meristem itself. This Cap also secretes Mucigel as a lubricant to allow movement through the soil. This Cap is regularly shedded like a snake skin and replaced. ○ Root Apical Meristem The entire area of cells contained by the Root Cap. Most of the cell division is actually directed away from the Root Cap. This Meristem creates the Primary Tissues: Protoderm, Ground Meristem, and Procambium. ■ Protoderm creates the Dermal Tissue. ■ Ground Meristem creates the Parenchyma cells. ■ Procambium creates the Vascular Tissue. ○ Quiescent Center This is an area within the Apical Meristem where the cells do not reproduce as quickly as other cells. They are resistant to damage from chemicals and radiation, which makes them a workable reserve of cells if the rest of the Meristem is damaged, ○ Zone of Elongation The cells in this area of the root can lengthen by 10 times their original length and help to push the root down and through the soil. ○ Zone of Maturation The area of cell differentiation and tissue specialization. This has “root hairs,” which are small follicles of the root 3 that reach into areas of the soil that the rest of the root cannot reach due to their small size. ○ Root Anatomy ■ Monocots ● Epidermis Composed of Dermal Tissue and protect the root. ● Cortex Composed of Ground Tissue and store the products of photosynthesis and work to absorb nutrients. ● Endodermis A cylindrical, singlecell wall of cells between the Cortex and the “stele,” which is a central core of vascular tissue. Contains the Casparian Strip. ● Vascular Tissue Xylem and Phloem in a ring format in the center. ■ Dicots ● Epidermis Composed of Dermal Tissue and protect the root. ● Cortex Composed of Ground Tissue and store the products of photosynthesis and work to absorb nutrients. ● Endodermis A cylindrical, singlecell wall of cells between the Cortex and the “stele,” which is a central core of vascular tissue. Contains the Casparian Strip. ● Pericycle Inside the Endodermis and is responsible for the formation of Lateral (sideways) roots. ● Vascular Tissue Xylem and Phloem in an X format in the center. ● Primary Growth in Shoots ○ Apical Meristems Domeshaped bud of dividing cells at the tip of the stem. Creates the three types of Meristems like in roots: protoderm, ground meristem, and procambium. ○ Axillary Meristem Regions of meristem tissue left after the apical meristem grows further. A dormant region but can become active in order to form branches. ■ Lateral Meristems These are not actual tips in most cases, these are on the outer edges of the plant like a second skin. They allow the plant to grow in width, which is called Secondary Growth. This type of growth is only found in Dicots. ● Secondary Growth in Shoots Lateral Meristems increase the plant’s width by generating Secondary Vascular Tissue (meristems made by tissues to help with secondary growth: Vascular Cambium and Cork Cambium) and Periderm. ○ Vascular Cambium A cylinder of meristem tissue that produces additional Xylem and Phloem. These cells come from the Procambium (part of the vascular bundles) and the Interfascicular Parenchyma cells between the vascular bundles (the first word just means between the bundles). These two forms of cells create a single ring of cells that is called the Vascular Cambium (which just means a ring of vascular tissue). ■ Division Patterns ● Multiplicative Division When the cells all divide as separate units that continue to divide further. Many 4 more initial cells and increase the circumference of the VC by widening the ring. ● Additive Division The cells divide but one cells remains to become a Phloem or Xylem mother cell, which just turn into their respective cell types. ○ Cork Cambium A new protective tissue that replaces the Epidermis when it falls off as the plant grows in width. Basically a new skin. It is a meristematic tissue that originally formed the outer cortex (the meat of the plant) and now produces Cork Cells, which act as the protective layer on the outside. Like human skin cells, these cells produce a waxy substance that hardens them until they die in order to protect themselves. Its called Suberin. The Cork Cambium and the Cork Cells together are referred to as the Periderm. Bark is Periderm with the Phloem. Plant Behavior ● Plant Behavior is any response they have to specific stimuli. ● Internal Stimuli Biological Clocks and Hormones are controlled by the plant and are regulated by alternations of night and day. Their actions include Leaf Movement, Flower Opening, and Fragrance Emission. ● Environmental Stimuli are any outside forces acting on the plant. They are Physical, such as light and wind, and Biological, such as predators and chemicals. ● Plant Cell Signals ○ Plants react to changes in their environment via specific cell signals such as hormones. There are three stages to Cell Signaling: Receptor Activation (a signal binds to a protein receptor on a cell wall), Signal Transduction via Secondary Messengers (a molecule is released into the cell by the activated protein receptor), and Effector Release (the cell responds with an Effector that directly influences the cellular response to the stimulus. ○ Hormones ■ Chemical signals that have a variety of effects depending on what they are released into and what other hormones are activated alongside them. ■ Auxins The “master” hormone that is produced in the apical meristems and young leaves. The main example is Indoleacetic Acid (IAA). ● AuxinResponsive Genes The expression of these genes is promoted by Auxin. When there is a low level of Auxin repressor proteins prevent the gene expression and when there is a high level of Auxin the repressor proteins break down and the expression is enhanced. ● Auxin Transport Auxin mainly flows in a downward fashion from the shoots to the roots. It is produced in the tips of young leaves and it is moved directly from one Parenchyma Cell to the next. Uncharged molecules (IAAH) enter cells by diffusion but charged ones (IAA) require the aid of transport proteins. Auxin Influx Carriers (AUX1) carry Auxin into the cells and PIN Proteins help it move out of the cells. ● Function of Auxin It establishes the apicalbasal polarity of seed embryos. It allows for the differentiation of vascular tissues from the undifferentiated cells. It mediates Phototropism (growth towards sunlight) and promotes the growth of roots and fruits. ■ Cytokinins Chemicals such as Zeatin. These chemicals increase the rate of cell division and are mainly present in the root/shoot tips and seeds. They also have a role in the seed and flower production and control leaf senescence (aging). 5 ■ Gibberellins More than 100 forms of Gibberellic Acids. They are produced in the apical buds, young leaves, and embryos. They interact with with light and other hormones to foster seeds, help stems grow and flowering, and slows down leaf and fruit aging. ■ Ethylene Coordinates plant development and stress responses. It is produced during seedless growth, flower growth, and fruit ripening. It causes leaf and petal senescence and drop. It helps as defense against osmotic stress and pathogens and influences cell expansion. It is often used in coordination with Auxin. ■ Abscisic Acid Stress hormone. It stops or slows metabolism during unfavorable environmental conditions, It stimulates the formation of protective scales around the buds of Perennial Plants. ■ Brassinosteroids Stress hormone. It is found in all parts of most plants and causes vacuoles to increase their water intake. It allows for cell expansion, impedes leaf dropping, stimulates the development of Xylem, and allows for the alteration of carbohydrates in the cell wall. ○ Responses to Environmental Stimuli ■ Photoperiodism the plant’s ability to measure and respond to the amount of light in an area and the length of the day. It is not actually measuring the light but the time of the darkness. This response is generated via light receptors within the cells and results in: Sun Tracking (motion of the plant to turn towards the light), Phototropism (growth of the plant towards a light source), and determines Flowering and Seed Germination. ● Periods ○ LongDay Plants Flower in Spring or in early Summer. They flower when the night is shorter than the day. This includes beets, radishes, and spinach. ○ Shortday Plants Flower in late Summer, Fall and Winter. They flower when the night is longer than the day. This includes poinsettias, soybeans, and chrysanthemums. ○ Dayneutral Plants They flower no matter what the time period of darkness. This includes corn, sunflowers, and roses. ○ Responses to Shade The plant extends leaves from shady regions towards regions of light via elongation of branches. ● Receptors ○ BlueLight Receptors Cryptochromes. They tell seedlings if there is enough light available to perform photosynthesis, if there isn’t enough then they “tell” the seedling to grow taller. The main one is Phototroponin. ○ Red and FarRed Receptors Phytochromes. They have great control over Photoperiodism. Angiosperms use it to regulate the time of their flowering. ■ Gravitropism Plants grow in response to gravity. Roots exhibit Positive Gravitropism because they follow gravity by going downwards. Shoots exhibit Negative Gravitropism because they go against gravity by going up. The two parts of the plant will do this no matter how the seedling is placed in the ground. ■ Thigmotropism Plants respond to physical contact with objects. Roots that encounter rocks use this response to override their Gravitropism response to force the root to grow horizontally around the rock/barrier until the Gravitropic response can reactivate. ■ Flooding When roots are drowned they are unable to absorb sufficient oxygen. To protect themselves they produce Aerenchyma, which are tubes for air channelling within the root that are created by collapsing cells with ethylene. 6 ■ Drought Drought has a similar response to that of high salinity (salt content) and temperature shifts because all of them decrease the water content of cells. Abscisic Acid manages this response and allows for the Aquaporin (channels that allow intake of water at an extremely fast pace) to open and close. Drought stressed plants also close their stomata to prevent water loss. ■ Herbivores and Pathogens Plants have structural barriers such as the cuticle (waxy coating), epidermal trichomes (basically thorns and burrs), and bark. In the case of herbivore attack plants have chemical responses too in that they can deter the herbivores and summon the predators of those herbivores. Plant Nutrition ● Macronutrients are nutrients that the plant needs in at least 1 gram per 1 kilogram of dry plant mass. Micronutrients are only needed at .1 gram per 1 kilogram. ● Light ○ Light is necessary for photosynthesis. Plants adapted their leaves to be sun leaves or shade leaves. Shade leaves have thinner leaves to let more light filter through and produce more chlorophyll to gather more available light. Sun leaves are thicker, have less spaces for air and more stomata. The arrangement of the leaves is also key; tropical plants that don't see much light on the forest floor have long stems with leaves only at the very top. Excess light can damage chloroplasts so they change their position in the plant. Some carotenoids (light absorbing chemical) absorb excess light and dissipate it as heat. UV radiation can be absorbed by the cuticle. carotenoids, and the flavonoids. Plants that can do this are usually brightly colored. ● CO2 ○ Most of dry plant mass is C2 Plants cannot obtain enough to reach maximum photosynthetic potential. When there are hot, dry conditions the stomata close as well and the plant can’t absorb CO2either. ● HO 2 ○ Water is the source of most of the Hydrogen and much of the Oxygen in organic compounds in plants. Water acts as the solvent and is used as a transport medium for plants. Plants are 90% water and most will die if they go below half that normal amount. Plant Transport ● Plasma Membrane Transport Mechanisms ○ Passive Transport (Does not require ATP) ■ Diffusion movement across a membrane. Uncharged particles only. Osmosis is water diffusion. ■ Aquaporin Large channels for water to allow for rapid intake. ■ Facilitated Need minor help to move across the membrane. ● Channels Pores that allow for up to 100 Million molecules per second to move through. ● Transporters The molecule binds on and changes the protein shape, which releases it. Allows for 100 1000 molecules per second. ○ Active Transport (Requires ATP to move it across membrane or against concentration gradient (moving from low concentration to high instead of the reverse). ● Turgor Pressure Turgor Pressure is the pressure against the cell wall. ○ Turgid Cells These cells are full of water and the Plasma Membrane is pressed tightly against the Cell Wall, which makes them rigid. This occurs when the plant is placed in a Hypotonic Solution. ○ Flaccid Cells These cells have a fair amount of water and the Plasma Membrane is not pressed against the Cell Wall as tightly. This occurs when the plant is placed in a Isotonic Solution. 7 ○ Plasmolyzed Cells These cells have so little water that there is a space between the Plasma Membrane and the Cell Wall. This occurs when the plant is placed in a Hypertonic Solution. ○ Water Potential Ψw is the symbol. ■ The potential energy of water. It is directly influenced by the concentration of solutes and the presence or absence of a cell wall. It is measured in Megapascals (MPa) and water moves along the Water Potential Gradient, from an area of high Potential to low. The Water Potential is equal to the Solute Potential(determined by presence or absence of solutes) plus the Pressure Potential, which is determined by the hydrostatic Pressure (whethe the cell is Turgid, Flaccid, or Wilted/Plasmolyzed, which makes the Pressure Potential positive, equal, or negative respectively. This is written as Ψw = Ψs + Ψp ■ Relative Water Content A measurement used to gauge the normal water content of a plant or one of its organs. This is used to calculate whether a plant is able to recover from water loss. ○ Osmotic Stress ■ Plants adapt to Osmotic Stress (rapid change in water movement/location) in two main ways. ● They can increase the solute concentration of the Cytosol (the fluid in the cell) in order to decrease the Water Potential and draw the water into the cell. The solute addition lowers the freezing point of the Cytosol. ● They can open or close Aquaporin Channels in the Plasma Membrane allow water to rush in or out depending on the need. ● Short Distance Transport ○ Transmembrane Transport The movement of materials between two cells via transport proteins. This leads to repeated crossing of cell membranes and walls and is, in practice, like a line of people passing a bucket of water down the line. ○ Symplastic Transport Movement of materials from cell to cell via the Plasmodesmata. These are small tubes that link cells together and allow for quick transport by just moving through the tube. There are two parts to this transport: Protoplasts (the contents of a single cell including its cell wall) and the Symplasts (the Protoplasts plus the Plasmodesmata). ○ Apoplastic Transport An Apoplast is the “empty” space between the cells. Materials can move through this space. This is for quick and easy transport of water and minerals. ○ Concept Visual ■ Think of this transportation as though each cell is a building in New York. Transmembrane Transport would be like one person throwing an item from their window to a person in the building over and that person doing the same to the other person and so on. Symplastic Transport would be like having walkways between the buildings for people to go straight across between the buildings. Apoplastic Transport is like moving through the streets below to walk into the buildings. ● Long Distance Transport ○ Movement from the Roots to the Shoots and Leaves can be difficult. This is mainly in trees, especially since some trees can grow taller than 110 meters (roughly 360 feet). For this movement, Xylem and Phloem are used because they are extensive, branched vascular tissues. ■ These Vascular Tissues allow for Bulk Flow, which is the mass movement of liquid or material due to gravity, pressure, or both at once. Bulk Flow is faster than diffusion. ○ Xylem ■ In Angiosperms Xylem has specialized cells and their structures are important to their function. Tracheids and Vessel Elements are separate structures but both function mainly for water uptake, which makes them both Xylem structures. ● Parenchyma Cells Living at maturity. They have thin, flexible cell walls and remain alive into their mature stage. They act as enablers for the metabolic 8 functions of the plant. They usually have one large vacuole (water storage organelle). Many Parenchyma can actually change into other specialized cells given the proper conditions such as damage repair. ● Vessels ○ Tracheids Dead at maturity. Long, narrow cells with slanted end walls that fit together like a puzzle. They have lignin rings around their walls to allow for extension. Some areas have no lignin, these areas are called Pits. These “Pits” are parts of the wall that are 1 cell thick and are permeable to water. Water moves both vertically and laterally through these pits. ○ Vessel Elements Dead at maturity. They are arranged like pipes and are plentiful in angiosperms. They have wide diameters comparatively, which allows for greater bulk flow, and their cell walls are 2 cells thick and lignified (have lignin rings present). They too have Pits and the ends of their cells have large holes to connect them to the next Element and still allow Bulk Flow. ○ 2 Types of Water Conducting Cells are needed because both types are vulnerable to Embolisms (air bubbles that block the flow of water) caused by damage, drought, and freezing/thawing cycles. In woody plants these vessels can be completely blocked and if there were only one type of cells available the entire area they fed water to would die. ● Transpiration Transpiration is the loss of water by evaporation. This effect is used to force water upwards through the vessel cells. This requires no energy because it’s natural as the water warms within the plant. This effect is the main way that water is moved long distances through plants. 99% of the water absorbed by plants is evaporated away by Transpiration because its main function is to act as a transport mechanism for materials. ○ Stomata Stomata prevent the loss of this water by closing and allow it by opening. A Stomata is just the hole, it is closed or opened by the shrinking (close) or elongation (open) of Guard Cells around the hole. ○ Leaf Abscission When plants are under stress by having too little water they drop their leaves in order to prevent water loss and embolisms from air absorption. ○ Phloem ■ The main function of Phloem is to transport sugars and minerals. There are two different types of Phloem: 1 Cell and 2 Cell. 1 Cell is in the Vascular Bundles and is comprised of Sieve Tube Elements and Companion Cells. 2 Cell is in the Inner Bark and is comprised of Fibers and Parenchyma Cells. ● SieveTube Elements Living at maturity. Cylindrical cells stacked on one another with holes in their end walls. ● Companion Cells They help to repair STEs ^. They cause P Protein to collect on the Sieve Plate (the junction between two STEs) to block loss from the Phloem and prevents pathogens from infecting the cells. ■ Phloem Loading The active movement of sugar into the STEs. The main form of the sugar is Sucrose because it is less likely to break down during transport. ● Woody Plants In woody plants Symplastic Transport is used and the Sucrose is moved from a higher concentration to a lower one. ● Herbaceous Plants In nonwoody plants Apoplastic Transport is used and Sucrose is usually moved from a higher concentration to a lower one. This requires energy to move it across the cell membranes. 9 ■ Pressure Flow Hypothesis ● Phloem Transport is driven by turgor pressure differences between the cells where the sugar is made (source) and the cells where the sugar is used (sink). The movement of Sucrose requires the Plasma Membrane, which explains why the STEs are alive at maturity. Whenever the concentration of solute in the Phloem decreases, water flows from the Phloem to the Xylem, which explains why they are located so close together. Plant Reproduction ● Sexual Reproduction ○ Alternation of Generations Plants have two multicellular lifecycle stages and most have both stages present on the main body. ■ Sporophyte The diploid, spore producing generation. This is the Dominant Generation in all plants except the Bryophytes. ■ Gametophyte The haploid, gamete producing generation. ○ Flowers Reproductive shoots that are branches specialized for reproduction instead of leaves. They are thought to have evolved from leaflike structures and are produced by apical meristems. ■ Whorls and Organs There are 4 Whorls to Flowers. A Whorl is a concentric ring of flower organs. ● Sepals They form the Calyx Whorl. They function to protect the unopened flower bud. They are usually small and green but some are colored and they generally remain around the base of the flowers. ● Petals They form the Corolla Whorl. Together with the Calyx Whorl they form the Perianth. They function to attract pollinators. ● Stamens They form the Androecium Whorl. They produce spores. They are composed of a Filament and Anther. ○ Filament The stalk supporting the Anther ○ Anther The chunk of plant material at the top. They are composed of 4 Microsporangia. ■ Microsporangia Produce the Microspores. Sacks of Microspores. ■ Microspores Mother Cells that develop into Pollen. ■ Pollen Grain Immature male gametophytes. The wall between 2 Microsporangia breaks down to form one Pollen Sac. The anther then splits to release the Pollen. ● Has 2 layers: the Exine (thick layer of Sporopollenin one of the most resistant biological materials in existence. Pollen pores where this material is thin or absent) and Intine (super thin inner wall). ● Has 2 Cells The Generative Cell (forms 2 Sperm Cells) and the Pollen Tube Cell (forms the Pollen Tube). ● Carpels They form the Gynoecium Whorl. They produce and enclose the female gametophytes. It is a vase shaped and vascular tissues deliver nutrients from the Sporophyte (remainder of the plant body) to it. One or more Carpels fused are called a Pistil. 10 ○ ○ Pistil single or a fused Carpel. ■ Stigma The top of the Carpel. Receives the Pollen. ■ Style The elongated portion of the Carpel. ■ Ovary Produces and Nourishes the Ovules ■ Ovule The Spore Producing Structure enclosed in Teguments. ● In the ovary a Megaspore mother cell divides by meiosis to produce 4 Megaspores, 3 of which die and 1 remains alive to become the Functional Megaspore. This divides by Mitosis to produce a 7 cell gametophyte that has 8 nuclei: 6 cells have 1 nucleus and 1 cell has two. ○ 1 cell is the Egg Cell ○ 2 are Synergids, which surround the Egg Cell and help to guide the Pollen Tube to the Egg ○ 3 are Antipodal Cells, which lie at the opposite side of the above 3 and their function is unknown ○ 1 cell is the Central Cell and has the two other nuclei. This cell forms the Endosperm. ■ Complete vs. Incomplete Flowers with all 4 Whorls vs. 1 or more missing Whorls. ■ Perfect vs. Imperfect Have stamens and Carpels vs. Have one or the other. Staminate flowers have only Stamens and Carpellate have only Carpels. ■ Dioecious vs. Monoecious The Staminate and Carpellate Flowers are on different plants vs. on the same plant. ○ Pollination and Double Fertilization ■ Pollination The Pollen Grain is deposited on the Stigma. The Stigma and Style determine whether the Pollen Grain is compatible and, if so, the Pollen Grain hydrates and germinates. The Pollen Tube Cell extends through the Style into the Ovule and deposits the two Sperm Cells. ■ Double Fertilization 1 Sperm fuses with the Egg to become the Zygote, which becomes the Embryo. The other fuses with the Central Cell nuclei to form the first endosperm cell. ○ Embryos and Seedlings ■ The Embryo is a young, multicellular, diploid sporophyte. The first cell division in the Zygote is unequal, one cell is much larger than the other and this established the ApicalBasal Polarity. The smaller cell develops into the Embryo while the larger cell becomes the “Suspensor.” This “Suspensor” channels nutrients and hormones from the parent sporophyte to young embryo. This slowly disappears and then older embryos rely on the Endosperm. ■ Young dicot embryos are spherical but they become heart shaped as the Cotyledons (the precursor to the first leaves) develop and curl to fit inside the seeds. 11 ■ Mature monocot embryos are cylindrical and have a single Cotyledon. ■ Seeds only develop from fertile ovules, which means it contains an embryo and Endosperm. Seeds have a tough coat produced by the Sporophyte Integuments. All done with this section! Good luck y’all!
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