Which of the following characteristics of aquaporins ensure that the channel selectively transports only water molecules and not other solutes? choose one or more:
a. the channel has a narrow pore that is only wide enough for a single water molecule to pass through.
b. the channel undergoes conformational changes to push water through the channel.
c. two asparagines in the center of the pore prevent protons from passing through the channel.
d. a glutamate at the entrance to the channel prevents positive ions from entering the channel.

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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b. the carbon cycle ensures living things have a source of hydrogen