3. Phosphorus represents only 1% of human body weight. However, it is a building block of very important macromolecules. Describe some of the cellular functions that would not be possible without phosphorus.

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.