Question

1.In response to seasonal changes in temperature, many organisms must alter the composition of their plasma membranes to maintain the proper degree of fluidity. Which change in the fatty acids of phospholipids would be most effective in maintaining membrane fluidity in a colder environment?

A. an increase in phospholipid fatty acid side chain length and an increase in side chain saturation

B. a decrease in phospholipid fatty acid side chain length and an increase in side chain saturation

C. a decrease in phospholipid fatty acid side chain length and a decrease in side chain saturation

D. an increase in phospholipid fatty acid side chain length and a decrease in side chain saturation

2. Refer to Animation: Fluid Mosaic Model. Although the phospholipid molecules can be in constant lateral movement, they very rarely flip from one side of the bilayer to the other. Which of the answer choices could explain this?

A. The head groups are repelled by the hydrophobic membrane interior.

B. The cholesterol keeps the phospholipids on the correct side.

C. The head groups are too large to fit between the interior fatty acid tails.

D. The molecular attraction between the fatty acid tails is too strong.

Answer 1

1) saturated fatty acids can be packed efficiently so the saturated fatty acids decrease the fluidity, at a lower temperature due to decrease in temperature the fluidity decreases, and the length of the whole bilayer decreases, so if the bilayer contains more saturated fatty acids then the fluidity decreases at lower temperatures, to increase fluidity at lower temperatures concentration of unsaturated fatty acids has to be increased,unsaturated fatty acids have double bonds, so a kinks forms there and unsaturated fatty acids cannot be packed efficiently, at lower temperatures the thickness of lipidi bilayer decreases so to increase the thickness, lipid with long fatty acid chains has to be inserted in to the bilayer so the answer is D. an increase in phospholipid fatty acid side chain length and a decrease in side-chain saturation