And in this particular case, they have to use another method. And what they use is these integral proteins, transmembrane proteins that exist inside our cells. So we have one integral protein shown here and another one shown here. Now, these are also known as transport membrane proteins because we find the proteins in the membrane and their function is to transport move these molecules across the two sides of the membrane. Now, we can categorize, we can break down these membrane proteins, transport membrane proteins into two types. We have membrane channels and we also have membrane pumps.