How do cells get their functions? Is there a particular time for cells to operate?
A cell is an organism with its own biological clock. They regulate themselves and undergo division and regeneration automatically. They move, breed and grow independently and respond to changes in their environment. They generate their own energy and store it away to use later.
The bulk of the cells in the human body look alike and have the same abilities. Other cells specialise in certain functions, and that determines what they look like and what they do. Nerve cells are designed to transmit messages around the nervous system, muscle cells grow in bundles so they can contract and reproductive cells combine to create new life.