Final answer:
Integral proteins are the membrane proteins that penetrate into the hydrophobic part of the lipid bilayer, where they can function as channels or pumps for substances moving in and out of the cell. The correct option is a.
Step-by-step explanation:
The kind of membrane protein that penetrates into the hydrophobic part of the lipid bilayer is the integral protein. These proteins are integrated completely into the membrane structure, with their hydrophobic regions interacting with the hydrophobic core of the phospholipid bilayer. They can span all or part of the membrane and may serve as channels or pumps to move materials into or out of the cell. Unlike integral proteins, peripheral proteins are more loosely associated with the lipid bilayer and do not penetrate into the hydrophobic interior. Glycoproteins can be a type of integral protein or peripheral protein, but the term specifically refers to proteins that have carbohydrate groups attached to them. Transport proteins can be a subset of integral proteins, as they assist in the movement of substances across the cell membrane.