回顧問題不定期更新 Study Questions are Made by Prof. Cruz & Prof. Moore from Oberlin College & Conservatory?

Lecture 5: Osmosis & Homeostasis

1.What is the difference between osmosis and diffusion?

2.Examine the diagram provided here.

a)Is Compartment A hyperosmotic relative to Compartment B? Why or why not?

b)The dashed vertical line that separates the compartments is semi-permeable, allowing only water and not the solute (in this case, sugar) to pass through. Draw an arrow to indicate the direction in which osmosis will occur.

c)If salt (Na+ and Cl- ions) is added to Compartment A, will the direction of osmosis change? Why or why not?

d)How many salt molecules will need to be added to Compartment B to prevent water from moving into Compartment A?

e)How many water molecules have to be added to Compartment A to prevent osmosis from occurring altogether?

3.Freshwater fishes don’t drink, but saltwater fishes do. Explain how these behavioral differences make sense in terms of regulating the water balance in their bodies (homeostasis).

4. Both saltwater and freshwater fishes have “salt pumps” (membrane proteins capable of moving Na+ across the lipid bilayers of their gills). Explain the differences in these salt pumps, given that freshwater and saltwater fishes have different water concerns. (How do these salt pumps work in each case?)

5. Certain clams, such as those that live in estuaries, are able to adjust to the changes in salinity (‘saltiness’) of the water, as happens frequently and regularly in estuaries. Would such clams produce more urine when the water around them is saltier than usual, or not? Explain your answer.

6.What is the difference between active transport and passive transport? Is the entry of H+ into the mitochondrial matrix from the intermembrane space during oxidative phosphorylation an example of active or of passive transport? Explain your answer.

7.If active transport is “energetically expensive”, why do cells do it at all?

8. How do the flame cells of a planaria worm get rid of its dissolved nitrogenous waste?

9. Being terrestrial and possessing relatively small body sizes (large surface area relative to body volume), insects have a fantastic ability to prevent water loss. For example, they have water-impermeable exoskeletons, they void nearly dry feces, and they do not pee. What role do Malpighian tubules play in recovering water from the gut so it returns to?the hemolymph and does not go out the anus?

10. Birds that live in saltwater habitats (like penguins) have specialized salt glands that enable them to withstand the large amount of salt in their environment. How do these glands work?

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