Question

example of a protein pump; transport sodium ions out of the cell and potassium ions into the cell.
glycolipids
peripheral proteins
sodium - potassium pumps
glycoproteins

Explanation:

The problem is about a protein pump (sodium - potassium pump) and cell membrane components. This relates to the study of cells and their functions, which falls under Biology (a subfield of Natural Science). The sodium - potassium pump is a key concept in cell biology, specifically in the study of cell membrane transport mechanisms.

Answer:

The subfield is Biology (under Natural Science).