Chapter 1 Biology_ the Study of Life - DOC by keara


									Chapter 24 Reproduction in Plants Chapter Outline I. With a Little Help A. Pollination requires mechanism of transport for pollen. 1. Transfer from male structure to female structure. 2. Possible mechanisms include: a) Wind – used by oak trees. b) Attraction of pollinators (insects) – rose plants. 1) Use smell and sight to attract. B. Dispersal of seeds may require an external mechanism. 1. Transport of seeds away from parent plant – enhances survival. 2. Angiosperms enclose seeds in fruit. a) Some release seeds to be dispersed via wind. 1) Orchid seeds are very small and light – no special adaptations. 2) Dandelion fruit – have modifications like parachutes for transport. 3) Maple fruit – two large seeds with extensions (wings). b) Some fruit is heavy. 1) Cannot be transported by wind. 2) Recruits animals to disperse. c) Fleshy fruit develops to attract animals by sight, smell, and taste. 1) Berries – Edible fruit with small seeds. 2) Peach has soft outer layers and hard center – stone. 3) Fruit develops green (unnoticed) and ripens to attract. 4) Entices animals to eat the fruit and disperse the seeds. 5) Animal vectors include: birds, mammals, and reptiles. d) Some fruit develop into nuts that animals eat. 1) Some of the embryos in the seeds are eaten. 2) Some are stored by squirrels or blue jays and grow where stored. e) Dry fruits may split open to disperse seeds. 1) Some attract animals like ants with rewards (oil/vitamin deposits). 2) Ants disperse the seeds into the colony, effectively planting them. 3) 1/3 of herbs in the U.S. are dispersed by ants. f) Some fruit is dispersed by clinging to animals. 1) Hooks and spines attach to fur – dispersal. II. Sexual Reproduction in Flowering Plants Is Suitable to the Land Environment -Critical concepts include: flower anatomy, alternation of generation, sporophyte, gametophyte, pollination, coevolution, and double fertilization. 24.1 Plants have a sexual life cycle called alternation of generations A. Angiosperms – Flowering plants. B. Diversity is a factor of specialized lifecycle. C. Flowers – Reproductive structure in angiosperms. 1. Produces seeds covered by a fruit. 2. Consists of four whorls of modified leaves.


a) Receptacle – Base of flower where whorls attach. 1) Attached to the end of the flower stalk. b) Sepals – Outermost whorl. 1) Most leaf-like – typically green. 2) Function – Protection of developing flower (buds). 3) Can resemble petals – as seen in the daylily. c) Petals – Second whorl from the outside. 1) Typically colored. 2) Function – attract pollinators. 3) Variation on size, shape, color, and scent – directed at pollinators. 4) Can be fused together – forms a floral tube. i) Accommodates special mouthparts of distinct pollinator. 5) Nectar – Sweet solution secreted at the base of petals. 6) Wind pollinated flowers typically do not have petals. d) Stamens – Third whorl from the outside. 1) The male portion of the flower. 2) Consists of two parts. i) Anther – Saclike container containing pollen grains. ii) Filament – Slender stalk that connects anther to receptacle. 3) Pollen grains must reach the female part for reproduction. e) Carpel – Center of flower. 1) Vaselike structure – female portion of flower. 2) Consists of three parts. i) Stigma – Enlarged knob, sticky for capturing pollen. ii) Style – Slender stalk. iii) Ovary – Enlarged base that encloses the ovules. 3) Ovules – Structure where eggs develop. 4) Fertilization of an egg with a sperm (pollen) produces a seed. 5) Ovary with fertilized egg develops into fruit. D. Flowering plants can be monocot or eudicot. 1. Monocot flowers. a) Flower parts occur in multiples of three. 2. Eudicot flowers. a) Occur in multiples of four or five. E. Complete flowers–contain all four whorls. F. Incomplete flowers are missing one or more whorls. G. Perfect flowers have both stamens and carpels. H. Imperfect flowers are missing either the stamens or carpels. 1. These are unisexual flowers. 2. Staminate – Contain stamens. 3. Carpellate – Contain carpels. 4. Monoecious – Plant with both staminate and carpellate flowers. a) Ex.: Corn. 5. Dioecious – Staminate and carpellate flowers on separate plants. a) Ex. Holly. I. Flowering Plant Life Cycle.


1. Alternation of Generations. a) Diploid sporophyte alternates with a haploid gametophyte. b) Multicellular forms of sporophyte and gametophyte exist. c) Sporophyte – Diploid, produces haploid spores via meiosis. d) Gametophyte – Haploid, produces haploid gametes via mitosis. e) Fertilization returns to the diploid sporophyte. f) Sporophyte generation is dominant over gametophyte generation. g) Gametophyte is nutritionally dependant on sporophyte. 2. Seed plants produce two types of spores – evolutionary adaptation. a) Microspores develop into male gametophytes – pollen grains. 1) Produced in the anther. 2) Microspore mother cells undergo meiosis – microspores. 3) Microspores undergo mitosis  two-celled grain. 4) Generative cell divides to produce two sperm cells. 5) Pollen grains are dispersed (wind or animal). 6) Pollen tube develops on compatible female carpel. 7) Germinated pollen grain = mature male gametophyte. 8) Two sperm cells move to female gametophyte (down tube). b) Megaspores develop into female gametophytes. 1) Remains in the flower – protected from desiccation. 2) Megaspore mother cell undergoes meiosis. 3) Occurs in the ovule of the ovary of the carpel. 4) Megaspore undergoes mitosis – produces 7-celled embryo sac. 5) Embryo sac – mature female gametophyte. 6) Contains the egg. 7) Post fertilization, the ovule becomes the seed. 3. The seed contains both food and embryo. a) Seed coat surrounds and protects the embryo and food. 4. Fruit develops from the ovary – aids in dispersal. 5. Seed germination – development of new sporophyte generation.
24.2 Pollination and fertilization bring gametes together during sexual reproduction A. The lifecycle of angiosperms protects from desiccation. B. Pollination – Pollen transfer from anther to stigma. 1. Self-Pollination – Pollen and stigma from the same plant. 2. Cross-Pollination – Pollen comes from a different flower of same species. a) Offspring have different genotype than parents. 3. Mechanisms of cross-pollination. a) Wind pollination is typical of grasses, gymnosperms. 1) Produce massive amounts of pollen. 2) Ex.: Single corn plant – 20-50 million grains per season. b) Animal pollination – most angiosperms. 1) Insects (bumblebees, flies, butterflies, moths). 2) Birds (hummingbirds). 3) Mammals (bats). 4) Unique to angiosperms (utilization of animals). C. Coevolution – One species changes in pace with a second species.


1. Two species become suited to each other. 2. Plants that attracted pollinators had survival advantage. 3. Pollinators that associated with flower had food source. 4. Modern flowers have anatomy that directs pollinators to pollen. 5. Pollinator mouthparts are suited to access the nectar. 6. Examples. a) Bee-pollinated flowers. 1) Typically yellow, blue, or white. 2) Have ultraviolet markings – nectar guides. 3) Bees have feeding proboscis of proper length to collect nectar. 4) Bees have pollen basket on hind legs – carry pollen. D. Double Fertilization. 1. Unique to angiosperms. 2. Results in formation of zygote and food source (endosperm). 3. Mature male gametophyte donates two sperm cells. a) Pollen tube grows into the embryo sac. 1) Pollen tube is extension of the pollen grain. 2) Digests its way through the stigma and style. 4. One sperm fertilizes the egg  zygote  sporophyte. 5. One sperm unites with two polar nuclei centrally located in embryo sac. a) Forms a 3n endosperm nucleus. 1) Develops into the endosperm – nutritive tissue (energy source). 6. Ovule now develops into the seed. a) Seed coat forms from ovule wall. 7. Mature seed contains: a) Embryo. b) Stored food. c) Seed coat. 8. Cotyledons – seed leaves are an alternate food source. a) Takes up the endosperm. III. Seeds Contain a New Diploid Generation -Critical concepts include: embryo development, fruit characteristics, and germination. 24.3 A sporophyte embryo and stored food develop inside a seed A. Zygote forms following fertilization. 1. Asymmetrically divides. a) Small cell with dense cytoplasm. 1) Becomes proembryo – gives rise to embryo. b) Large cell. 1) Divides to form suspensor with basal cell. 2) Attach embryo to parent plant – transfers nutrients. 3) Disintegrates later in development. B. Globular Stage. 1. Forms from repeated mitotic divisions. 2. Proembryo exists as ball of cells.


3. Root-shoot axis is established. a) Cells near suspensor will become root. b) Cells at opposite end become shoot. 4. Determination of tissues. a) Outermost cells will become epidermal tissue. 1) Divide perpendicular to surface. 2) Produce single cell layer. 3) Protects plant from desiccation. C. Heart Stage. 1. Cotyledons develop. a) Give characteristic shape to embryo. b) Monocot cotyledon. 1) Stores nutrients. 2) Absorbs nutrients from endosperm. c) Eudicot cotyledons are primary food source for embryo. D. Torpedo Stage. 1. Cotyledons elongate via cell divisions. 2. Surrounding endosperm is used. 3. Tissues become differentiated. 4. Root and shoot apical meristems are distinguishable. 5. Primary meristems (ground meristem) are present. E. Mature Embryo Stage. 1. Epicotyl is present – region of stem above cotyledons, contributes to shoot. 2. Hypocotyl is present – stem region below cotyledons (not root). 3. Radicle is present – embryonic, young root. 4. Cotyledons well developed, fold over. 5. Procambium develops future vascular tissue. 6. Development stops at this stage – enters dormancy. 24.4 The ovary becomes a fruit, which assists in sporophyte dispersal A. Fruit. 1. Develops from ovary. 2. Protects and aids in dispersal of seeds. a) Attraction of animals. b) Provides nutritious reward. 3. Ovary wall becomes pericarp. a) Three layers. 1. Exocarp – outermost. 2. Mesocarp – middle. 3. Endocarp – inner. B. Fleshy Versus Dry Fruits. 1. Dry Fruit characteristics. a) Pericarp is dry at maturity. b) May open and release seeds at maturity. 1) Dehiscent opens at maturity. 2) Indehiscent does not open at maturity.


c) Examples: 1) Pea pod – opens on two sides to release seeds (dehiscent). 2) Maple tree fruit – indehiscent with wings. 3) Cereal grains (wheat, rice, corn) – indehiscent fruit with seeds inside. 2. Fleshy Fruit characteristics. a) Pericarp remains fleshy at maturity – berries. 1. Ex.: Tomato. b) The endocarp can become hard (stony) – drupes. 1. Ex.: Peaches and cherries. C. Simple Versus Aggregate and Multiple Fruits. 1. Simple Fruits. a) Derived from simple ovary of single or compound ovary with fused carpels. 1) On one flower. 2) Simple ovary – one chamber. 3) Compound ovary – multiple chambers (number of carpels). b) Ex.: Tomato. 2. Accessory Fruits. a) Contain flower parts other than ovary. 1) May include the receptacle – apple is mostly receptacle. 3. Aggregate Fruits a) Compound fruit. b) One flower with multiple ovaries. c) Ex.: Strawberry. 4. Multiple Fruits. a) Compound fruit. b) Many flowers with single carpels that fuse together. c) Ex.: Pineapple. 1) Also an aggregate fruit – parts of flower trapped between carpels. 24.5 With seed germination, the life cycle is complete A. Germination – Growth of embryo into a seedling plant. 1. Requires adequate environmental conditions. a) Water, warmth, and oxygen. b) Ensures no growth in unfavorable conditions. 2. Length of dormancy varies. a) Can occur even if environmental conditions are favorable. b) Some seeds require cold period to break dormancy. c) Bacterial action on seed coats can break dormancy. d) Fire can break some seed dormancy. 3. Fleshy fruits have inhibitors to stop germination. a) Ensures no growth within the fruit. B. A rudimentary plant is present between eudicot cotyledons (bean). 1. Contains immature leaves. C. Seedling growth.


1. Shoot is hook-shaped – protects immature leaves as they emerge. 2. Cotyledons provide food for developing seedling. 3. True leaves develop later and then uses photosynthesis. D. Corn kernel germination. 1. The kernel is the fruit with a seed/embryo inside. 2. Has a single cotyledon. 3. Immature root and leaves covered by sheaths. IV. Plants Can Also Reproduce Asexually -Critical concepts include: asexual reproduction strategies, and tissue culture techniques. 24.6 Plants have various ways of reproducing asexually A. Reproduce sexually or asexually. B. Sexual Reproduction. 1. Offspring are genetically different from parent. 2. Have advantage of survival in different environmental conditions. C. Asexually reproduction – Vegetative reproduction. 1. Offspring are genetically identical to the parent plant. 2. Beneficial in unchanging environment. 3. Favorable in agriculture because plant maintains desirable characteristics. 4. Examples. a) Stolons – Aboveground horizontal stems. 1) Axillary buds develop from nodes on stolon. 2) Ex.: Strawberry. b) Rhizomes – Underground horizontal stems. 1) Typical of irises and grasses (sod forming plants). 2) Nodes bear buds which grow into new plants. 3) Tubers are enlarged rhizomes – potato. i) Act as storage organs in the plant. c) Corms – Bulbous underground stems. 1) Not true bulbs. d) Bulbs – Composed of modified storage leaves around short stem. 1) Ex.: Onions. e) Suckers – Small plants emerging from roots (fruit trees). f) Propagation from stem cuttings. 1) Used with pineapple, sugarcane, azalea, etc. 2) Uses hormone (auxin) to stimulate root development. 24.7 Cloning of plants in tissue culture assists agriculture A. Tissue Culture – Growth of tissue in artificial liquid/solid medium. 1. Produces new plant (clone). 2. Totipotent – Cells have genetic capability to make entire new plant. 3. Somatic Embryogenesis. a) Hormones generate masses of cells. b) New plants develop from cells – typically genetically identical. c) Used for:


1) Tomato, asparagus, lilies, begonias, and African violets. d) Somaclonal Variations. 1) Give rise to genetic variation. 2) Used to generate new plants with desirable traits. 4. Clonal Plants. a) Use of meristem tissue to produce new plants. b) Addition of hormones stimulates organ development. c) Used with orchids. d) Plants tent to be virus free. 5. Anther Culture. a) Haploid cells in pollen grains are cultured on a medium. b) Produces haploid plants. c) Can be used to generate diploid plants that are clones. 6. Cell Suspension Culture. a) Extract chemicals from plant cells growing on media. b) Avoids having to collect plants from the environment. c) Examples. 1) Cinchona produces quinine. 2) Digitalis produces digitalis, digitoxin, and digoxin. V. Connecting The Concepts A. Flowering plants dominate the biosphere. B. Homo sapiens evolved in a world dominated by angiosperms. C. Early humans were predominantly herbivores. 1. Relied on food from plants (fruits, nuts, seeds, tubers, roots, stems, leaves). D. Plants provided shelter from the environment to humans. E. Civilization depended on the development of agriculture. 1. Flowering crops: corn, rice, wheat. 2. Others include: coffee, spices, sugar, rubber, tea. F. Even today we depend on plants to live. 1. Currently even more important than early in our evolution. 2. Used in many modern, industrial applications. 3. Also used for their aesthetic value. G. Half of all pharmaceutical drugs originate from plants. 1. Loss of rainforests or plant in general will be devastating. a) Loss of medicines and ecosystem balance.


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