Ch32.pdf - Chapter 38 Notes Plant Reproduction and Biotechnology I Sexual Reproductive structures of flowering plants A Life cycle of angiosperms

Ch32.pdf - Chapter 38 Notes Plant Reproduction and...

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Unformatted text preview: Chapter 38 Notes Plant Reproduction and Biotechnology I. Sexual Reproductive structures of flowering plants A. Life cycle of angiosperms characterized by alternation of generations between sporophyte and gametophyte stages 1. Plants reproduce sexually, often relying on pollinators to bring sperm and egg together. 2. The sporophyte (diploid) develops from the zygote by mitosis and produces haploid spores; it consists of roots, stems, leaves, and flowers. 3. Meiosis of cells within flowers produces the small haploid gametophytes, which in turn produce either sperm or eggs. B. Components of flowers 1. The specialized parts of the flower grow from the modified end of the floral shoot – the receptacle. a. Sepals (collectively called the calyx) are the outermost green, leaflike parts. b. Petals (collectively called the corolla) are the colored parts located between the reproductive structures and the sepals. 2. Flowers differ from the outer tissues of the plant in their fragrance and colors (carotenoids and anthocyanins), which are attractive to pollinators. C. Where pollen and eggs develop 1. Male parts, called stamens, are located inside the corolla. a. The stamen consists of a slender stalk (filament) capped with an anther. b. Inside the anthers are pollen sacs in which pollen grains develop. 2. Female parts are located in the central part of the flower. a. The carpel is the vessel-shaped structure with an expanded lower chamber (ovary), slender column (style), and upper surface (stigma) for pollen landing. b. In the ovary, eggs develop, fertilization occurs, and seeds mature. 3. So-called “perfect” flowers have both male and female parts (may or may not be on the same plant); “imperfect” flowers lack the parts of one sex. II. A new generation begins A. From microspores to pollen grains 1. In anthers, each diploid “mother” cell divides by meiosis to form four haploid microspores. 2. Each microspore will divide to form pollen grains. [8/26/2019 12:45:37 PM] Chapter 38 Notes 3. One cell in each pollen grain will produce the sperm; the other will form the pollen tube. B. From megaspores to eggs 1. In the carpel, a mass of tissue forms an ovule (potential seed) enclosed by integuments. 2. A diploid “mother” cell divides by meiosis to produce haploid megaspores, one of which will undergo mitosis three times to produce a cell with eight nuclei. 3. The nuclei migrate resulting in an embryo sac (female gametophyte) with seven cells; one cell has two nuclei and will become the endosperm (nutrition for the embryo); another cell will be the egg. C. From pollination to fertilization 1. Pollination is the transfer of pollen to the surface of the stigma by the actions of insects (70% of the time), birds, or wind. 2. In germination, a pollen tube forms producing a path that the two sperm will follow to the ovule. 3. When the pollen tube reaches an ovule, it penetrates the embryo sac, and the two sperm are released to undergo double fertilization. a. One sperm fuses with the egg nucleus to form a diploid zygote. b. The other sperm nucleus fuses with the two endosperm nuclei to yield a triploid “primary endosperm cell” that will nourish the young sporophyte seedling. III. From zygote to seeds and fruits A. Formation of the embryo sporophyte 1. The zygote undergoes repeated divisions to form an embryo sporophyte as a part of an ovule and is accompanied by formation of a fruit. 2. Cotyledons (seed leaves) develop for the purpose of utilizing the endosperm during germination. B. Seed and fruit formation 1. From zygote to embryo, the plant supplies nutrition until the time when the connection between the ovule and ovary wall is broken. 2. The mature ovule’s integuments thicken into seed coats around the seed (a mature ovule containing embryo and food reserves). 3. A fruit is a mature ovary with seeds (ovules) inside; they may be classified as simple, aggregate, multiple, or accessory. 4. The pericarp of a fruit consists collectively of: endocarp (around the seed), mesocarp (fleshy portion), and exopcarp (skin). C. Structures of the mature seed 1. Seed coat -- protects the seed and the embryo within the seed 2. Embryo a. Cotyledon -- seed leaves [8/26/2019 12:45:37 PM] Chapter 38 Notes b. Hypocotyl -- portion of the embryonic axis below the cotyledons attachment point which terminated in the radicle (i.e., embryonic root) c. Epicotoyl -- portion of the embryonic axis above the cotyledons which contains the plumule (i.e., shoot tip with miniature leaves) IV. Dispersal of fruits and seeds A. Seeds have coevolved with particular dispersing agents: currents of air or water, or animals passing by. 1. For example, the pericarp of maple seeds extends out like wings to catch the wind and be transported far from the parent tree. 2. Some fruits are dispersed by sticking on animal bodies or by passing through the digestive tract to be deposited in the feces. B. Humans are perhaps the grand dispersing agents by virtue of the long distances to they carry seeds, by design or by accident. Dormancy -- condition of low metabolic rate and a suspension of growth and development in a seed as it matures and dehydrates; increases the chances that germination will occur at a time and place most advantageous to the seedling VI. Germination -- from seed to seedling and is dependent on physical process of imbibition (i.e., uptake of water due to the low water potential of the seed) A. Factors necessary for germination 1. Water 2. Temperature -- some seeds need extended exposure to cold temperatures 3. Light -- some seeds need to be buried shallow to allow for light exposure VII. Asexual reproduction of flowering plants A. Asexual reproduction in nature 1. Vegetative growth modes include runners, rhizomes, corms, tubers, and bulbs. 2. Parthenogenesis, embryo development from an unfertilized egg, can produce new orange plants. B. Induced propagation 1. Vegetative propagation (cuttings) can result in new plants produced from leaves that form roots. 2. Tissue culture propagation can result in whole plants produced from a group of cells. VIII. Plant Biotechnology -- use of genetically modified plants in agriculture and industry A. Examples 1. Bt toxin -- gene introduced into maize, cotton, and potatoes to protect them from serious insect pests and eliminates need for spraying pesticides 2. Gene introduced into some plants that makes them resistant to herbicides so weeds could be controlled but not [8/26/2019 12:45:37 PM] Chapter 38 Notes affect the main crop 3. Disease resistant genes 4. Genes to increase the nutritional quality of the plant such as vitamin A where blindness is prevalent in third world countries whose diet is deficient in vitamin A B. Disadvantage -- could produce a "super weed" if a gene escaped and underwent crop-to-weed hybridization [8/26/2019 12:45:37 PM] ...
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  • Plant morphology, Megaspores

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