Apentix/AP Biology/Unit 2: Cell Structure and Function/Question
AP Biologymediummcq1 pt

A membrane rich in cis-unsaturated fatty acid tails behaves differently from one rich in saturated tails because the unsaturated tails:

A.carry positive charges that repel one another inside the bilayer core
B.are shorter, which thins the membrane and speeds every kind of transport
C.bind cholesterol irreversibly and lock the membrane into place
D.carry kinks that keep neighboring tails from packing tightly, raising fluidity

Explanation

Core Concept

Each cis double bond puts a permanent bend in a hydrocarbon chain, so unsaturated tails occupy more room and make fewer close contacts with their neighbors. Weaker packing means a lower temperature is needed before the bilayer gels, so such membranes stay fluid in the cold. Organisms living in chilly environments raise the share of unsaturated tails in their membranes for exactly this reason.

Correct Answer

Dcarry kinks that keep neighboring tails from packing tightly, raising fluidity

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