Aquaporins exclude passage of hydronium ions (H₃O+), but some aquaporins allow selection of glycerol, three-carbon alcohol, as well as H₂O. Since H₃O+is closer in size to water than glycerol is yet cannot pass through, what might be the basis of this selectivity?

Hydronium ion in chemistry is known to form due to the protonation of water. It is a positive ion that is known to define Arrhenius acid. It is well established that it provides protons to the surrounding medium of water.

Glycerol is known for its simplicity in chemistry. It is odorless and colorless. It is present in a liquid state. It is made from three carbons and belongs to the alcohol category.

Aquaporins are the kind of channel proteins present in the membrane of the cell. These are concerned with the transport of the water in the cells.

Without these, water cannot pass through the membrane quickly as water is a polar molecule. It tremendously increases the rate of water transport in the cells.

Hydronium ion is not transported with the help of the aquaporins because it contains charge in its structure. On the other hand, glycerol is not a charged structure; however, it is big, but clearly, the charge in the structure is a matter of concern for aquaporins, not the size.

Size of hydronium, however small or almost equal to water, but this property does not guarantee the passage through aquaporins. Similar size does not make hydronium ion liable for transport through the water protein channel.