What do we call the small pores in a membrane through which diffusion takes place?

The answer to this is number 1. Aquaporins. This integral membrane is responsible for providing the needed channels so that water can be transferred easily. You can just imagine how hard it would be when these channels do not exist in order to serve as the passageway of water between the different cells of living things.

There are times when there are some small solutes along the membrane. This integral membrane can be found in a lot of living things. There are some studies that show that each aquaporin molecule that can be found within the membrane has a pore. The 4th option may be considered too but aquaporins are considered the correct term.