Third set of review questions for the third hour exam If all the calcium phosphate is dissolved out of a BONE, what sort of thing is left? A brittle object the same size and shape of the original bone? A flexible, rubbery object the same size and shape of the original bone? A shrunken object, smaller but otherwise the same shape as the original bone? An inflated, larger object, bigger, but approximately the same shape of the original bone? Something else? What? The result cannot be predicted? If all the COLLAGEN were somehow digested or otherwise removed from a BONE, which of the results listed above should occur? If all or many of the sulfate groups were somehow digested or otherwise removed from a CARTILAGE, which of the listed results should occur? If all or most of the COLLAGEN were somehow digested or otherwise removed from a CARTILAGE, which of the listed results should occur? (If in doubt, explain your reasoning.) How could any of these 4 changes in bones or cartilages (maybe) be of medical use? * Given the fact that electro-osmotic pressure (and osmotic pressure too) is a scalar variable, and that the elasticity of collagen networks is a fourth order tensor, which do you suppose causes the shaping of cartilages and bones? Please explain your reasoning. (The answer isn't quite as simple as you might guess). * Look at the changes in sizes and shapes of chondrocytes near where ossification is occurring. Which of the following could provide the directional driving force that elongates growing leg bones, arm bones, and ribs? (Based on what you know about electro-osmosis; based on what you can see about cell shapes, sizes and arrangements?) The chondrocytes orient their mitotic divisions, so that these will push in the longitudinal direction? The chondrocytes secrete more sulfonated sugar chains from those sides of the chondrocytes that face the directions of elongation? The chondrocytes cause digestion of sulfonated sugar chains in the locations closest to where new bone is forming? The chondrocytes cause digestion of collagen fibers that resist osmotic swelling of cartilage? * Which of these explanations above are taught in medical schools? Which are asserted on most informational web sites (e.g. Wikipedia) about endochondral ossification? *Which of these explanations are logically possible? What experiments can you invent to prove or disprove each of these theories? * Can you invent some additional theories to explain how bones "grow" in length? When you inflate a long balloon, does it grow? Does pressure become greater in certain directions? * Do capillaries and other blood vessels GROW? (Partly yes, partly no.) Please explain. Do cartilages GROW in length or width? (Partly yes, partly no.) Please explain. Do bones GROW in length or width? (Partly yes, partly no.) Please explain. Are the shapes of cartilages necessarily the result of more growth in some directions and/or locations? (Partly yes, partly no.) Please explain. Contrast the difference in results of cutting or otherwise removing collagen fibers of bone versus removing or cutting collagen fibers from cartilage. Possible answer: Bone gets weaker, but doesn't change shape. Cartilage swells = enlarges, by osmotic (electroosmotic swelling). (Equivalent to increased inflation of a balloon in which the rubber is weakened. ) * Predict the effect of cutting a slice in the surface of a cartilage. Would the expected effect differ depending on whether the cut is parallel or perpendicular to the long axis of a leg cartilage? * Bones have many blood vessels running through them, but cartilages don't. A widely-believed explanation is that cartilage matrix proteins inhibit formation of blood vessels. Can you suggest another possible explanation? * What if blood vessels formed along the surfaces of cartilages, but rarely penetrated into their interior. What sort of explanation would that support? What if blood vessels rarely even ran along the outside surfaces: what would that suggest. * Which parts of the body form or grow by expansion pressure of water. What parts grow by osmotic swelling. Explain why cartilage can grow by internal swelling, but bone can't. Would internal swelling be possible if cells secreted some material that is not subject to any form of osmotic pressure? --------------------------- 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, corals and sponges somewhat more like plants, at least superficially? indeterminate growth and shape What are meristems? What are two kinds of meristems, located in different parts of plants? What is a cambium? What function does a cambium serve? If a given species doesn't have any cambia? (=plural of cambium) (Latin second declension, neuter), how will that limit its growth? What geometric shape is a cambium? cylindrical What is a "cork cambium"? Where is it located? What does it produce? bark In plants, mitotic divisions are located where? in meristems and cambia 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?br> auxin How is plant cell growth related to weakening of cellulose cell walls? 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 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 substances 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. (This is a sick joke) 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 ias a result of a broken gas pipe) What is the name of at least one other plant hormone, besides auxin?