To produce proteins for the rest of the cell to function.
They would not be able to survive in an environment without sunlight. For instance, they would not be able to survive in caves, because they need sunlight for food and if there is no sunlight then they can not create food and would starve.
<span>First, chemical energy from organic molecules is used to make ATP (Adenosine triphosphate) in cellular respiration, after which ATP provides energy for biological processes.</span>