Answer:
A. The channel has a narrow pore that is only wide enough for a single water molecule to pass through.
Explanation:
Aquaporin water channels are integral membrane proteins present in plants and animals. Their main function is to transport water across the cell membrane responding to osmotic gradients. It is suggested that steric factors (volume of the molecule) and electrostatic interactions are responsible for their selectivity for water, also the presence of an aromatic/arginine constriction retains the protons.
Considering this information we can conclude that the correct answer is A. The channel has a narrow pore that is only wide enough for a single water molecule to pass through.
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