Multiple Choice
Which statement best describes the structure of the cell (plasma) membrane?
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8. Membrane Structure
The Lipid Bilayer
Multiple Choice
In the context of the lipid bilayer, what is the primary role of cholesterol in the cell membrane?
A
It buffers membrane fluidity and stability by preventing extreme packing at low temperatures and excessive fluidity at high temperatures.
B
It forms aqueous pores that allow large polar molecules to diffuse freely across the membrane.
C
It serves as the main covalent cross-linker that permanently locks phospholipid tails together.
D
It provides most of the membrane’s selective ion transport by functioning as an ATP-driven pump.
Verified step by step guidance1
Understand the structure of the lipid bilayer: it is primarily composed of phospholipids with hydrophilic heads and hydrophobic tails, creating a semi-permeable membrane.
Recognize that membrane fluidity is crucial for cell function, allowing proteins to move and the membrane to self-heal, but it must be regulated to prevent damage from temperature changes.
Recall that cholesterol molecules insert themselves between phospholipid tails within the bilayer, influencing how tightly these tails pack together.
Analyze how cholesterol acts as a buffer: at low temperatures, it prevents phospholipids from packing too tightly, maintaining fluidity; at high temperatures, it restrains excessive movement, maintaining stability.
Conclude that cholesterol's primary role is to modulate membrane fluidity and stability, rather than forming pores, cross-linking lipids, or directly transporting ions.
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