This is a type of protein found in the cell membrane, which regulates the coming and going of substances into or out of the cell.

Carrier proteins are the proteins present in the cell membrane which regulates the coming and going of substances into or out of the cell.

These carrier proteins can transport the molecules with the concentration gradient in the case of facilitated diffusion or can transport the molecules against the concentration gradient by using energy in the form of ATP in case of active transport.

Large, polar and charged molecules like amino acids, nucleosides, and ions are transported through carrier proteins. Binding of molecules to these proteins induce the conformational change in the proteins which allow the protein to be open from the opposite side to transport the molecule across the membrane.

the answer would be..

b. sucking