Question

researchers analyzed the composition of cell membranes of bacteria living in different environments.
thermophiles are bacteria that live at extremely high temperatures, typically at or above 70°c.
which of the following best predicts the effect of a greater proportion of saturated fatty acids, as
compared with unsaturated fatty acids, on the stability of the cell membrane in thermophiles?

a
a greater proportion of saturated fatty acids has no effect on cell membrane stability
because both saturated and unsaturated fatty acids are hydrophobic.

b
a greater proportion of saturated fatty acids leads to increased membrane stability
at lower temperatures because saturated fatty acids increase the stability of the
membrane.

c
a greater proportion of saturated fatty acids leads to decreased membrane stability
because saturated fatty acids decrease the fluidity of the membrane.

d
a greater proportion of saturated fatty acids leads to increased membrane stability
at higher temperatures because saturated fatty acids pack tightly together.

Explanation:

To determine the correct answer, we analyze the effect of saturated fatty acids on cell membrane stability in thermophiles (bacteria living at high temperatures, ≥70°C).

• Option A: Incorrect. Saturated and unsaturated fatty acids do affect membrane stability (saturated fatty acids increase stability, unsaturated increase fluidity).
• Option B: Incorrect. Thermophiles live at high temperatures, so the explanation about "lower temperatures" does not apply to their environment.
• Option C: Incorrect. Saturated fatty acids increase (not decrease) membrane stability. Saturated fatty acids have straight tails that pack tightly, reducing fluidity and increasing stability.
• Option D: Correct. Thermophiles live at high temperatures. A greater proportion of saturated fatty acids increases membrane stability because saturated fatty acids have straight hydrocarbon tails that pack tightly together. This tight packing helps the membrane maintain its structure and stability at high temperatures, where increased fluidity (from unsaturated fatty acids) would be detrimental.

Answer:

D. A greater proportion of saturated fatty acids leads to increased membrane stability at higher temperatures because saturated fatty acids pack tightly together