Chapter 38 Angiosperm Reproduction and Biotechnology
Q: Distinguish between pollination and fertilization.
A: In angiosperms, pollination is the transfer of pollen from an anther to a stigma. Fertilization is the fusion of the egg and sperm to form the zygote; it cannot occur until after the growth of the pollen tube from the pollen grain.
Q: What is the benefit of seed dormancy?
A: Seed dormancy prevents the premature germination of seeds. A see will germinate only when the environmental conditions are optimal for the survival of its embryo as a young seedling.
Q: If flowers had shorter styles, pollen tubes would more easily reach the embryo sac. Suggest an explanation for why very long styles have evolved in most flowering plants. A: Long styles help to weed out pollen grains that are genetically inferior and not capable of successfully growing long pollen tubes.
A: No, the haploid (gametophyte) generation of plants is multicellular and arises from spores. The haploid phase of the animal life cycles is a single celled gamete (egg or sperm) that arises directly from meiosis: there are no spores.
Angiosperm reproduction involves an alternation of generations between a multicellular diploid sporophyte generation and multicellular haploid gametophyte generation. Flowers, produce by the sporophyte, function in sexual reproduction The four floral organs are sepals, petals, stamens, and carpel. Sepals protect the floral bud. Petals help attract pollinators. Stamens bear anthers in which haploid microspores develop into pollen grains containing male gametophytes. Carpel contains ovules (immature seeds) in their swollen bases. Within the ovules, embryos sacs (female’s gametophytes) develop from megaspore. Pollination which precedes fertilization is the placing of pollen on the stigma of a carpel. After pollination, the pollen tube discharges two sperm into the female gametophytes. Two sperm are needed for double fertilization, a process in which on e sperm fertilized the egg, forming a zygote and eventually an embryo, which other sperm combines with polar nuclei, giving rise to food-storage endosperm. The seed coat enclosed the embryo along with a food supply stocked in either the endosperm or the cotyledons. Seed dormancy ensures that seed germinate only when conditions for seedling survival are optimal. The breaking dormancy often requires environmental cues, such as temperature or lighting changes. The fruit protects the enclosed seeds and aids in wind dispersal or in the attraction of seed dispersing animal. Q: what changes occur to the four types of floral parts as a flower changes into a fruit? A: after polllination, a flower typically changes into a fruit. The petal, sepals and stamen typically fall off the flower. The stigma of the pistil withers and the ovary begins to swell. The ovules (embryonic seeds inside the ovary begin to mature. 38.2
Q: The seedless banana, the world’s most popular fruit, is losing the battle against two fungal epidemics. Why do such epidemics generally pose a greater risk to asexually propagated crops? A: Asexually propgated crops lack genetic diversity. Genetically diverse population are less likely to become extinct in the face of an epidemic because there is a greater likelihood that a few individuals in the population are resistant. Q: Self-fertilization, or selfing, seems to have obvious disadvantages as reproductive “strategy” in nature, and it has even been called an evolutionary dead end” so it is surprising that about 20% of angiosperm species primarily rely on selfing. Suggest a reason why selfing might be advantageous and yet still be evolutionary dead end. A: in short term selfing may be advantageous in a population that is so dispersed and sparse that pollen delivery is unreliable. In the long term, however, selfing is an evolutionary dead end because it lead to loss of genetic diversity and may preclude adaptive evolution Q: Potatoes...
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