Question

cholesterol is an essential component of your cell membranes, in part because regulating the amount of cholesterol that is incorporated into the membrane helps cells to maintain the fluidity of their membranes. at a typical human body temperature, the presence of cholesterol in the membrane decreases fluidity—increasing the stiffness of the cells and keeping them from becoming floppy. however, at much colder temperatures, the presence of cholesterol actually keeps membranes fluid and prevents them from becoming stiff! cholesterol is important in the cell membranes of fish for the same reasons it is important for you, including regulation of membrane fluidity. what effect would the absence of cholesterol have on fish living in a very deep lake where the surface is warm and the depths are very cold? fish that are missing cholesterol will not be able to adapt as well to different temperatures within the lake so they will need to stay at a depth where the temperature is \just right\. that \just right\ temperature will depend on the properties of the other lipids in their membranes. fish that are missing cholesterol will have membranes that are too stiff when in the cold depths of the lake so they need to stay near the warm surface to keep their membranes fluid. fish that are missing cholesterol will have membranes that are too fluid when near the warm surface so they need to stay in the cold depths to keep their cells from being too floppy.

Explanation:

Cholesterol helps regulate membrane fluidity. At cold temperatures, it keeps membranes fluid; at warm temperatures, it decreases fluidity. Without cholesterol, fish can't adjust membrane fluidity to different lake temperatures (warm surface, cold depths). So they'd need to stay at a "just right" temperature (based on other lipids) as they can't adapt like with cholesterol.

Answer:

Fish that are missing cholesterol will not be able to adapt as well to different temperatures within the lake so they will need to stay at a depth where the temperature is "just right". That "just right" temperature will depend on the properties of the other lipids in their membranes.