What is the primary function of channel proteins in the cell membrane?
A) To catalyse protein synthesis
B) To permit specific substances to pass through the membrane
C) To store energy for active transport
D) To regulate membrane fluidity
E) To transfer DNA out of the cell
IMAT 2026 · Question 16
Q16 - Membrane transport
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The correct answer is B) To permit specific substances to pass through the membrane.
The lipid bilayer blocks ions and polar molecules. Channel proteins form water-filled pores that let a specific ion or molecule cross, always down its concentration gradient. This is facilitated diffusion: it needs no energy.
A) Incorrect: Protein synthesis is catalysed by ribosomes, not membrane channels.
B) Correct: Channels let specific substances cross the membrane.
C) Incorrect: Channels do not store energy. Active transport uses pumps powered by ATP or by ion gradients.
D) Incorrect: Membrane fluidity is regulated mainly by cholesterol and by how saturated the fatty acids are.
E) Incorrect: DNA is far too large to pass through a channel protein.
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