Several types of energy conversion occur
in cells. Respiration is the process by which
raw fuel energy is converted to a form that can be used
for cellular work. Cellular work is a set of
processes that includes routine housekeeping as well
as special functions such as mitosis. All cells
respire and do work. Photosynthesis is carried
out by the cells of green plants and algae, among others.
It is the conversion that provides food energy, directly
or indirectly, for every living organism on earth.