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What is the distinction between "stress" and "strain" in engineering? Why are they not synonyms? Is there some mathematical equation that relates stress and strain, at least approximately? This is called ?????'s Law? The slope of the graph in this "law" is called ?????'s ??????? ? What adjective is used to refer to materials for which there is a non-linear proportionality between stress and strain? Is it common for biological materials to have such non-linear proportionalities? (hint: yes, sure!) Are there some physical properties that don't (& can't) vary with direction? What word that starts with an S refers to this category of variables? Magnetic forces are vectors; and what does that mean? How is curvature defined? Does a big circle have a larger curvature than a small circle, or what? Does a circle have a constant curvature? What about a straight line? For what sort of surface is the curvature in all directions equal? For what shape is curvature zero in one direction, and some non-zero constant in the direction perpendicular to the direction in which it is zero? What are some examples of structures in the body that have this shape? On the surface of a saddle, what is peculiar about curvatures in perpendicular directions? When you stretch a soap film across an irregularly bent ring, then the curvatures in perpendicular directions have what mathematical relationship at each location of the film? * How can soap solve mathematical equations faster than a computer? ** When soap bubbles "pop", is it really because the equations become too difficult for them to calculate exactly what shape they should become? Why are soap bubbles spheres? What forces are counterbalanced at their surfaces? When an inflated balloon becomes spherical, what does that tell you about the amounts of stress in different directions at different points on their surface? If the stress were twice as strong in one direction than in the perpendicular direction, then what shape would that balloon be? * Could this be important for understanding blood vessels, and diseases of arteries? What are some examples of kinds of variables that can have different amounts in different directions at each location? Such variables are called ??????s. (that starts with a T, and will astonish a physicist if you tell them you covered them in a biology course). Embryos of most species start out as spheres: does this mean they are made of soap? What does a spherical shape imply about whatever forces are acting within it? *When some embryos change toward being cylindrical, does that mean they are changing from soap into rubber? What is an example of a shape that has spherical symmetry? (hint: duh!) Can mechanical forces have spherical symmetry? Do developing embryos become more symmetrical, or less symmetrical? Symmetry "breaking" refers to what sorts of events? Such events are contrary to Whose "Principle"? (Hint: What was Marie Sklowdowska's married name?) In embryonic development, what is are two specific examples in which radial symmetry is "broken" to a single plane of reflection symmetry? Ladders and centipedes have what kind of symmetry? Somite formation is breakage of what symmetry? The chemical reaction-diffusion systems invented by the mathematician Turing may explain what kind of symmetry breaking in embryos? *How could such chemical instabilities also break spherical symmetry? *Could tensor variables also "diffuse" or otherwise spread? *Could Turing's kind of pattern-generating mechanism use variables other than chemical concentrations? ** Could you revise the rules that such variables would need to obey (In Turing's pattern-generating mechanisms? (Hint: it's surprisingly easy!) In Kartegener's triad, what symmetry is being broken? Formation of the gray crescent reflects what change in the symmetry of what kinds of embryos? In the formation of the apical ectodermal ridge, what symmetry is being changed? Can you make a reasonable guess about what changes in mechanical forces cause the formation of the apical ectodermal ridge? *Can you see a paradoxical contradiction between the shape of the apical ectodermal ridge itself, relative to what is implied about stresses by the curvature of the developing limb bud itself? (Hint: what changes in locations and directions of stress in the ectoderm.) **How would you measure amounts of stress at different places on the surface of living cells; or on surfaces of living embryos; or within living embryos? On a flexible surface, the pressure difference from one side to the other side is related to stress and curvature by what mathematical equation? In the eye, does the cornea have less or greater curvature than the rest of the eye? *If you know what is meant by astigmatism, then how can it be explained in terms of the symmetry of forces acting in the structure of the eye? If you had a ray-gun that could change the amounts of stress in living tissues, then suggest some medical applications? The letter N and which other letters have what kind of symmetry? The letters A, B, C, D, E, K, M, etc. have what different kind of symmetry? Do the letters H and I have more, or less, symmetry that A, B, C etc.? How many planes of reflection symmetry does a starfish have? Compare this with the symmetry of a pluteus larva. * What limitations are there on the curvature of a surface at a given point? (Hint: what about the curvatures of the letters H and O) **In what senses are genes blueprints, and in what senses are they algorithms=recipes? *When cancers tend to grow into spheres, even when the cancerous cells are not normally spherical, nor part of spherical organs, does this suggest anything? *What is the symmetry of an aneurysm, relative to the normal symmetry of an artery? What do vertebrate limb buds develop into, besides wings? Embryonic regulation (like what happens after you split or fuse early embryos) also occurs in which specific embryonic rudiments? What does FGF stand for, that is related to limb bud development? In what two ways can you cause a fifth or sixth leg to grow out of the side of a vertebrate embryo? What are the names of the 3 axes of a limb bud's development of asymmetry? *Which of these is another way of saying medio-lateral? Describe the location and cellular structure of the AER and the ZPA? What do these initials stand for? How can you make a biplane chicken, with double wings, one above the other? What about how to make a chicken whose legs branch into two mirror-image ends? * Is the world really ready for such chickens? What caused those wild frogs to develop 5 or 6 hind limbs? What are some of the dangers of too much retinoic acid for a developing embryo (or a woman who may become pregnant)? **Do you suppose sonic hedgehog protein might help cure acne? What is apoptosis? What are several examples where apoptosis normally occurs? What abnormalities would develop in animals in which a mutation eliminated the ability of cells to undergo apoptosis? What medical uses can you suggest for a drug that temporarily prevents apoptosis? Suppose you were trying to produce chickens that could swim better; how would such a drug be useful? From what part of which of the 3 germ layers does the heart develop? How is the coelomic cavity formed in vertebrate embryos? Which embryonic organs have to develop very early? What are some organs that do not need to function until later? Contrast the development of the heart versus the kidneys, in terms of methods of improving an organ during development? What is the foramen ovale? What is the ductus arteriosus? In which directions does blood flow through them before birth? What happens to them at the time of birth, and afterward? Suppose that the septum between the right and left ventricles of the heart failed to develop: why would the baby be OK until birth? What circulatory problems would the baby then have, after birth? The muscles that make up the walls of the right and left ventricles have about the same thickness (and the same curvature) until birth, but as the baby grows, the wall of the left ventricle becomes about 4 times thicker that the wall of the right ventricle: what do you deduce from this? * Can you also figure out what difference develops in the curvatures of their walls? Hint: visualize the letters "Co", except with the o stuck up into the opening of the C.) Compare the curvatures of two bubbles, one big and one small, that share a common side. *Exercise makes muscles stronger, but do you suppose that they are responding to stress, or to strain? * How would the answer to this question relate to the effectiveness of different kinds of exercise? How are the relations of stress, pressure and curvature related to the ability of capillary walls to hold back as much pressure as the walls of arteries? Compare the cellular structures of arteries, veins and capillaries? What do they all 3 have in common, structurally? What are blood islands? What is vascularization? What are the differences between adult blood and that of developing embryos and fetuses? (Hints: differences in where the stem cells are located, and differences in hemoglobin). How might sickle cell anemia possibly be cured by changing the control of transcription of fetal hemoglobin genes? In what way is the control of hemoglobin genes (perhaps) analogous to the control of transcription of hox genes? (Hint: a difference between them is that one is controlled in time and the other in space, but...?) Can you list the organs that develop from each subdivision of the mesoderm? (hint: the subdivisions with the initial letters N, S (or P; which becomes D,M,S), I, and LP). Do male and vertebrates use the same (=homologous) duct (=pipe) to carry eggs and sperm out of the body? In other words, is the oviduct homologous to the sperm duct, in terms of the embryological development of each? What does each of them develop from? What happens to the other kind of duct in the other sex? In other words, do females not have a sperm duct because it became a sperm duct? What different reason is there? What is a pronephoros? Where does it develop? Where, and when, does the mesonephos develop? Do you still have either one of these organs in your body? (no, except a few of the tubules of the latter in males.) What purpose did the mesonephros serve when you were an embryo? What purpose do the few remaining mesonephric tubules serve in adult males? What are the different names of the duct that carries urine from the pronephros and the mesonephros. From what kidney do the ureters carry urine? What do those kidneys develop from? In the male vertebrate, what does the former urine duct develop into? And what is its new name? In mammals, the upper end of the oviduct is called ????, and the lower end develops into what? Which subdivision of which germ layer do oviducts develop from? Do the German names Mueller and Wolff remind you of anything? From what part of what germ layer do the gonads develop? Is this the same in both sexes? From what cells do the sperm and oocytes develop? Is this the same in both sexes? In either sex, do the gametes differentiate from cells that were originally part of the lateral plate mesoderm? Where do they come from? (Not from Aztlan!) How do they get there? * In the particular examples of mammals, birds, flies and nematodes, where do these cells come from? Compare the chromosomal mechanism of sex determination in flies and mammals (that is, what decided which individual will become a male or become a female?). How are these mechanisms similar? How are they really very different? What are some other methods of deciding sex, for example in turtles, alligators, birds, fish, and bees? If an individual has only one X chromosome, why will they become a male if they are a fly, but a female if they are a mammal? Where is the gene for "maleness" located in mammals? What is this gene called? *The textbook disparages the medieval view that being a female is equivalent to what one calls the "default condition" in the context of computer programs; but could you argue pro or con that is somewhat correct after all, on the basis of gene expression, hormone effects, or anatomical differences? * How is apoptosis (presumably!) involved in kidney development? What happens to people with mutations in their genes for testosterone receptors? *When chimeras are made by mixing morula-stage embryos of different sexes, guess what happens! Compare cartilage and bone: What are they made of? When they appear in development? What are the special advantages of each? |