Question

Which of the following factors does not affect membrane permeability?

a. The polarity of membrane phospholipids.
b. The saturation of hydrocarbon tails in membrane phospholipids.
c. The amount of cholesterol in the membrane.
d. Temperature Submit.

Answer 1

Membrane permeability is not affected by the polarity of membrane phospholipids, but by the saturation of hydrocarbon tails, cholesterol content, and temperature. Unsaturated fatty acids and higher temperatures increase fluidity, while cholesterol reduces it.

Step-by-step explanation:

The factor that does not affect membrane permeability is the polarity of membrane phospholipids (Option a). Membrane permeability is influenced by the saturation level of hydrocarbon tails in membrane phospholipids, the amount of cholesterol in the membrane, and temperature. Specifically, membranes with unsaturated fatty acid tails are more fluid because unsaturation introduces kinks that increase space between the phospholipid tails, enhancing membrane fluidity. The presence of cholesterol can decrease fluidity and permeability by filling spaces between fatty acids. Temperature also impacts membrane fluidity, as higher temperatures increase the movement of the phospholipid and protein components, thereby affecting permeability.

Organisms may adapt to temperature fluctuations by altering the saturation level of the lipids in their membranes. For example, an increase in unsaturated fatty acid content in response to cold temperatures helps to maintain membrane fluidity when the environment gets colder.

Answer 2

a. The polarity of membrane phospholipids.

Step-by-step explanation:

Phospholipids are the amphipathic lipids with polar heads and non-polar tails. The non-polar tails of two lipid layers form the core of the membrane while their heads are oriented towards both of the faces of the membrane. The polarity of the phospholipids does not affect the transport of substances. If a membrane has more of the saturated phospholipid tails in its core, the tight packing of the tails makes the membrane less permeable for large and polar substances.

On the other hand, a membrane with a greater proportion of unsaturated hydrocarbon tails in its core is more permeable. Cholesterol is also an amphipathic sterol and moderates the fluidity of membrane and thereby affects its permeability. A more fluid membrane is more permeable than a more solid membrane. Temperature affects the membrane polarity by affecting the membrane fluidity.