Chapter 38 Angiosperm Reproduction and Biotechnology 38. 1 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. Q: 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 (solanum tuberosum) and tomatoes (solanum lycopersicum) are fairly closely related species. If you managed to cross the two, would it be possible to have a hybrid that makes potatoes like tubers and tomatoes like fruits on the same plant?
A: this might be possible, but satisfactory results would be very unlikely. Both tuber and futis are tremendous energy sinks. Each plant has a only a finitie amount of energy to divide between sexual and asexual reproduction although ha tomato potatoes hybirid could, in theory produce offspring that makes fruits and tuber equally these fruits and tubers would be of inferior quality or low yielding. Asexual reproduction enables successful plants to proliferate quickly. Sexual reproduction generates most of the genetic variation that make evolutionary adaptation possible.
Plants have evolved many mechanism to avoid self-fertilization including dioece (male and female flowers on different individuals, non synchronous production of male and female part within a flower, and self incompatibility reactions in which pollen grains that bear an allele identical to one in the females are rejected. Plants can be cloned from single cells, which can be genetically manipulated before being allowed to develop into a plant. Q: what are the advantages and disadvantages of asexual reproduction?
A: asexual reproduction can be advantageous in a stable environment because individual plants that are well suited to the environment pass on all their genes to offsprings. Also asexual reproduction generally results in offspring that are less fragile than the seedlings produced by sexually reproduction. Sexual reproduction offers the advantage of dispersal of tough seeds. Moreover sexual reproduction produces genetic variety, which may be advantageous in an unstable environment. The likelihood is better that at least one offspring of sexual reproduction will survived in a change environment. 8. 3 Q: Compare traditional plant breeding methods with genetic engineering. A: Traditionally breeding and genetic engineering both involved artificial selection for desired traits. However genetic engineering techniques facilitate faster gen transfer and are not limited to transferring genes between closely related varieties or species. Q: Explain some benefits and risk of GM crops A: GM crops may be more nutritious and less susceptible to insect damage or pathogens that invade insect damaged plants.
They also may not require as much chemical spraying. However, unknown risk may include adverse effects on human health and nontarget organism and the possibility of transgene escape. Q: why does Bt maize have less fumonisin than non GM maize? A: Bt miaze suffers less inect damage, therefore Bt maize plants are less likely to infected by fumonisin producing fungi that infect plants through wounds. Q: In a few species, chloroplast genes are inherited only from sperm. How might this influence effort to prevents transgene escape?
A: in such species, engineering the transgene into the chloroplast DNA would not prevent its escape in pollen; such as method requires that cholorplast DNA be found only in the egg. And entirely different method of preventing transgene escape would therefore be needed, such as male sterility, apomixes, or self-pollinating closed flowers. Hybridization of different varieties and even species of plants is common in nature and has been used by breeders, ancient and modern, to introduce new genes into crops. After two plants are successfully hybridized, plant breeders select those progeny that have the desired traits.
In genetic engineering, genes from unrelated organism are incorporated into plants. Genetically modified (GM) plants have the potential of increasing the quality and quantity of food worldwide and may also become increasingly important as biofuels. Two important GM crops are golden rice, which provide more vitamin A and Bt maize, which is insect resistant. There are concerns about the unknow risk of releasing GM organisms into the environment, but the potential benefits of transgenic crops need to be considered. Q:give three examples of how genetic engineering has improved food quality or agricultural productivity?
A: Golden rice has been engineered to produce more vitamins A, thereby raising the nutritional value of rice. A Protoxin gene from a soil bacterim has been ergineered into BTmaize. This protoxin is lethal to invertebrates but harmless to betebraes. Bt crops require less pesticide spraying and have lower level of fungal infection. The nutritional value of cassava is being increase in may ways by genetic engineering. Enriched levels of proteins, iron, and betacarotene ( a vitamin aA precursor) have been achieved, and cyanide-producing chemical have been almost eliminated from the roots.
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