How can the number of channel or carrier proteins present in the membrane affect the rate of transport of substances into the cell?

The more protein channel or carrier a cell has, the faster will be the transport of a specific compound. In other side, lower will be the transport of the rest of compounds, such as O2, H2O.

Explanation:

A protein channel or a carrier protein acts as facilitators in the transport of compounds. The compounds who are polar can't pass easily, or can't even pass, trough the plasmatic membrane, because of it's nonpolar center. So, the cell needs to provide a way for the polar compounds who are needed inside or outside of the cell, thus we have the proteins channel or carrier. They form a polar way for the polar compounds pass into or out the cell.

However, the more proteins we have to transport, less space the membrane will have for the others compounds, because every transport protein just acts with a specific compound or others very similar to it.

answer: a. a gene that causes a specific trait.