Photosynthesis is often considered to be the single most important life process on Earth. It changes light
energy into chemical energy and also releases oxygen. Without photosynthesis, there would be no oxygen
in the atmosphere. Photosynthesis involves many chemical reactions, but they can be summed up in a
single chemical equation:
6CO2 + 6H2O + Light Energy → C6H12O6 + 6O2.
Photosynthetic autotrophs capture light energy from the sun and absorb carbon dioxide and water from
their environment. Using the light energy, they combine the reactants to produce glucose and oxygen,
which is a waste product. They store the glucose, usually as starch, and they release the oxygen into the
Cellular respiration actually “burns” glucose for energy. However, it doesn’t produce light or intense heat
as some other types of burning do. This is because it releases the energy in glucose slowly, in many small
steps. It uses the energy that is released to form molecules of ATP. Cellular respiration involves many
chemical reactions, which can be summed up with this chemical equation:
C6H12O6 + 6O2 → 6CO2 + 6H2O + Chemical Energy (in ATP)
Cellular respiration occurs in the cells of all living things. It takes place in the cells of both autotrophs
and heterotrophs. All of them burn glucose to form ATP.