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| Inquiry Questions None for this chapter. Self Test 1). If you could use a micro-laser to destroy the larger cell in a two-cell plant embryo, how would it likely affect embryonic development? a). The embryo would develop normally except it would not become anchored in the seed wall. b). The embryo would develop normally except it would have multiple cotyledons. c). The embryo would fail to develop, but a fully functional suspensor would form. d). The embryo would immediately be aborted, and the seed would not form. Answer: a 2). Loss-of-function mutations in the suspensor gene in Arabidopsis led to the development of two embryos in a seed. After analyzing the expression of this gene in early embryos, you find high levels of suspensor mRNA in the developing suspensor cells. What is the likely function of the suspensor protein? a). Suspensor protein likely stimulates development of the embryonic tissue. b). Suspensor protein likely stimulates development of the suspensor tissue. c). Suspensor protein likely inhibits embryonic development in the suspensor. d). Suspensor protein likely inhibits suspensor development in the embryo. Answer: c 3). How would plant development change if the functions of SHOOTMERISTEMLESS (STM) and MONOPTEROUS (MP) were reversed? a). The embryo-suspensor axis would be reversed. b). The embryo-suspensor axis would be duplicated. c). The root-shoot axis would be reversed. d). The root-shoot axis would be duplicated. Answer: c 4). The most obvious difference between plant embryonic development and animal embryonic development is that a). plants develop from unfertilized eggs, while animals develop from fertilized eggs. b). plant morphogenesis is entirely growth dependent, while animal morphogenesis involves movement of cells within the embryo. c). plant embryos have an available source of nutrients, while animal embryos must begin feeding to obtain nutrients. Answer: b 5). Which of the following is not evident from looking at a plant embryo? a). You can tell if the plant is a monocot or dicot. b). You can tell where the shoot will form. c). You can tell where the root will form. d). You can tell when the seed will germinate. Answer: d 6). Both seeds and fruits are well adapted to a). provide nutrition to animals. b). act as a dispersal mechanism for plants. c). allow plant embryos to remain dormant for long periods of time. d). all of the above Answer: b 7). The longest period of time that a seed can remain dormant is a). days. b). weeks. c). months. d). years. Answer: d 8). Fruits are complex organs that are specialized for dispersal of seeds. Which of the following plant tissues does not contribute to mature fruit? a). sporophytic tissue from the previous generation b). gametophytic tissue from the previous generation c). sporophytic tissue from the next generation d). gametophytic tissue from the next generation Answer: d 9). If you wanted to ensure that a seed failed to germinate, which of the following strategies would be most effective? a). prevent imbibition b). prevent desiccation c). prevent fertilization d). prevent dispersal Answer: a 10). How would a loss-of-function mutation in the α-amylase gene affect seed germination? a). The seed could not imbibe water. b). The embryo would starve. c). The seed coat would not rupture. d). The seed would germinate prematurely. Answer: b Test Your Visual Understanding 1). Label this diagram and predict the future axes of the plant. Answer: Labels: An arrow to the two dark green cells should say "first cell division." The taupe region above those cells should be labeled "endosperm" Future axis: Draw a line with arrows at both ends through the cells. The upward arrow should say shoot. The lower arrow should be labeled root. Refer to the second to last image from figure 36.2 on page 756, which shows that the prediction is correct. The shoot is upward and the root apex is downward. Apply Your Knowledge 1). You are writing a science fiction screenplay in which the best of animal and plant lifestyles and making a "super-species." Discuss the aspects of plant development you would include in this new species. Answer: You might want to incorporate a truly dormant stage in development so that the embryo could last for hundreds of years or develop immediately in response to environmental signals. Consider how far fruits and seeds travel. It might be fun to have an animal embryo inside a seed in a fruit that suddenly "germinates" on someone's dinner table. Many plants have axillary buds that replace the shoot if it is removed. Some form of backup "head" for your organism could add a bit of excitement to your screenplay. Remember that some animals also have the ability to regenerate, so this would not be a distinctly plant trait. Finally, plants are far easier to clone than most animals. Including this trait along with animal traits could add intrigue. 2). The oldest known seeds to successfully germinate were found in the Yukon Territory in the Canadian Artic in the 1950s. Radiocarbon dating found these seeds to be approximately 10,000 years old. Discuss the mechanisms that seeds use to remain dormant for long periods of time. Answer: Seeds can remain dormant for long periods of time because they have extremely low levels of water. This prevents biochemical reactions from occurring. By inhibiting biochemical reactions, not only is germination delayed, enzymes that might breakdown down the seed are also inhibited. The loss of water is triggered by hormonal action. Another mechanism that ensures long term dormancy is the formation of a hard, often light-proof, seed coat that both protects the embryo and blocks environmental signals, including water, that could trigger germination. Some seeds require a light signal to germinate. If the seed is deeply buried in the soil, it will not perceive a signal to germinate even if its seed coat is not very thick. 3). How might the reproductive success of angiosperms have changed if seeds had developed without fruit? Answer: Seed dispersal may be more limited in the absence of fruit. Animals that are attracted to the fruit and carry it and it's encased seed and embryo far distances may not be attracted to just the seed. With more limited seed dispersal, angiosperms may not have colonized so much of the terrestrial environment. |