Plasma Membranes

AP Biology· difficulty 3/5

A cell biologist measures membrane fluidity over a temperature range in cells with normal cholesterol versus cholesterol-depleted cells. The graph shows the result. The biologist then asks how cholesterol modulates fluidity at extremes of temperature.

Temperature Membrane fluidity no cholesterol + cholesterol cold hot

The role of cholesterol in animal cell membranes is BEST described as:

  • A

    A receptor for hormonal signaling only

  • B

    A channel for water transport

  • C

    An enzyme that synthesizes new phospholipids

  • D

    A buffering agent that decreases fluidity at high temperatures and increases it at low temperatures

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Explanation

Cholesterol restricts phospholipid motion at high temperatures and prevents tight packing at low temperatures, stabilizing fluidity across a temperature range.

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