Answer:
Because enzymes have many functions as chemical catalysts in numerous chemical reactions (for example in metabolism). By lowering the activation energy, they make it much easier to carry out reactions. They are also indispensable for signal transduction and cell regulation, often via kinases and phosphatases. They also generate movement, with myosin hydrolyzing ATP to generate muscle contraction, and also transport cargo around the cell as part of the cytoskeleton. Other ATPases in the cell membrane are ion pumps involved in active transport.