Second set of review questions for the third exam   What are cotyledons? Draw the shape and locations of the two cotyledons of a peanut. Is a plant seed equivalent to a newly laid egg; or is it more like a neurula stage that has gone into hibernation? What is the difference between cell walls and cell membranes? List major similarities and differences between development of higher plants and vertebrate animals. *How is development of colonial sea squirts and corals somewhat more like plants, at least superficially? What are meristems? What are several kinds of meristems, located in different parts of plants? What is a cambium? What function does a cambium serve? What geometric shape is a cambium? cylindrical What would a plant be unable to do if it didn't have any cambia? (=plural of cambium) (Latin second declension, neuter) What is a "cork cambium"? Where is it located? What does it produce? bark In plants, mitotic divisions are located where? In meristems and cambium Are these the same places that growth (in the sense of increases in volume) is concentrated? What function does osmotic pressure serve in plant growth? expands cells, often preferentially in certain directions or locations Compare the "growth" (enlargement and shaping) of plant stems and leaves with that of cartilages. What is an example of a plant hormone that can cause physical weakening of cell walls? How is plant cell growth related to weakening of cellulose cell walls? Hint: auxin By what systematic series of experimental procedures was indole acetic acid eventually discovered to be (the, until then hypothetical substance) "auxin"? Bioassay; you should be able to describe the experiments Besides stimulating elongation of shoots, what other effects has auxin also been discovered to stimulate? phototaxis, geotaxis, root formation, including redifferentiation of stem cells into root cells Which of these effects was used in the actual bioassays by which indole acetic acid was discovered to be auxin? Invent and describe a bioassay for discovering auxin by measuring each of the other three functions of auxin. What are anti-auxin herbicides, like 2,4-D? How were these (multi-billion dollar per year) herbicide chemicals discovered? (Or would you argue, either pro or con, that they were invented?) * (opinion) If you were a judge in a patent dispute between the discoverer of auxin and the inventor of 2,4-D, who deserves the royalties more? * (opinion) Depending on the outcome of such a patent lawsuit, on what efforts would (will) chemical companies concentrate their funding? *Based on auxin's different effects on plant cell enlargement and differentiation, would you expect Lewis Wolpert to regard auxin as a morphogen? *Why were the bioassays for identifying auxin so much more successful that the bioassays used to try to identify noggin, chordin, sonic hedgehog, fibroblast growth factor, or other substance that control animal structure formation? Hint: Suppose that the effects of auxin were shared by 5 or 6 different chemicals, any one of which could produce the same effect, by itself. Argue pro or con: Plant hormones like auxin would be called morphogens (and not hormones) if the occurred in animals, and the key difference is whether a substance produces a localized, long-term effect, as compared with an organism-wide short-term effect. Explain why a chemical morphogen will also be a teratogen. Hint: Because many mutations can cause birth defects *Design a bioassay for morphogens that works by comparing amounts of teratogenic effects (= birth defects). *Are such bioassays currently going on, unintentionally? Hint: yes If indole acetic acid were in diesel exhaust, how and when would auxin have been discovered? (Actually, ethylene was discovered to be a normal plant hormone in a similar way) What is the name of at least one other plant hormone, besides auxin?     TO BE CONTINUED   back to syllabus