Examples of Kuhn's Scientific Revolutions Producing New Facts, and New Questions.
Please answer, discuss, express your opinion, or explain why you don't have an opinion.

1) According to Steinberg's Differential Adhesion Hypothesis, if you measure how strongly aggregates of cells resist flattening by centrifugation and by physical pressure, then what property of cells are you measuring?
Answer: You are measuring reversible work of adhesion of cell to cell bonds

2) According to the "Differential Interfacial Tension Hypothesis", what property of cells are you really measuring when you observe and compare how much multi-cellular aggregates flatten in a centrifuge, or when squeezed by forces of known strength? (as above)
Answer: You are measuring force of active contraction of those parts of cell cortexes that are not in contact with other cells.

3) An important experimental confirmation of Malcolm Steinberg's theory is that those cell types which resist flattening the most are always the same ones that sort out to the more internal position. How else could you explain this accurate observation?
Answer: Sorting out is caused by differences in the same property that causes resistance to flattening?

4) Another experimental confirmation of the Differential Adhesion Hypothesis is that when cell type A gets engulfed by cell type B, then A flattens less than B in a centrifuge. Do you regard this as supporting evidence?
Answer: This type is too small to read; you will have to figure out the answer.

5) Do you think that the forces which cause gastrulation and neurulation have the same causes as cell sorting?     What about the forces that cause engulment?

6) Do regenerating salamander limb buds have gradients of contractile strength?

7) Visualize a sheet of cells that are wrinkling a rubber substratum, by means of their active contractility, and then more cells of the same differentiated cell type are allowed to settle onto the upper surface of the original cell sheet: Then do you predict any change in the force exerted on the rubber sheet?
Answer: Which theory predicts that interfacial contractility should be weakened?

8) When retraction fibers are re-inflated with cytoplasm (after mitosis, or in response to addition of increased calcium concentrations.
Please suggest at least two molecular mechanisms that could explain this re-inflation?

9) Does the rounding-up of cells help cytokinesis?     How?    Why?

10) True or false: Mechanical attachment of cytoplasmic actin to the plasma membrane is necessary for cytokinesis to occur.

11) (Why?) Would you expect that the basal ends (next to the cell body) of retraction fibers should move is (which?) certain directions just before cytokinesis, and after cytokinesis?

12) In regard to regeneration of arms and legs, which is more important?
a) Conversion of cells from one differentiated cell type to another? (metaplasia)
b) Locomotion of cells from certain positions to other positions? (motility)

13) Galvanotaxis means orientation and/or movement in response to electric fields:
Invent possible mechanisms, a) based on resting potentials of cells b) electrophoresis.

14) Suggest why all differentiated cell types have resting potentials (like nerves & muscles)


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