The chemical equation that summarizes the net reactants and products of photosynthesis can be summarized as follows: 6CO2 + 6H2O + light energy = 1 glucose + 6 O2. Carbon dioxide is the first of the reactants, which plants absorb from the atmosphere. Water is also an essential reactant, which is obtained from the plant's rooting systems or simple absorption for smaller autotrophs, or organisms capable of photosynthesis. The final ingredient is light energy, which involves the absorption of solar radiation by specialized organelles in plants known as chloroplasts.
The most widely useful product of photosynthesis is oxygen, which is used for aerobic metabolism by all animals on Earth. For high order animals to survive, they must deliver oxygen to all cells of the body. There is a symbiotic relationship between plants and animals; the oxygen produced during photosynthesis is a waste material for plants, and yet it is vital to animals' survival.
Glucose, the second product of photosynthesis, is composed of chemical bonds between atoms of carbon, hydrogen and oxygen. The solar energy that was originally absorbed by the plant exists in the form of these chemical bonds of glucose. The purpose of photosynthesis is to produce sugar, a high-energy chemical that acts as an energy reservoir for the plant. Solar energy is not always available, so plants have evolved the ability to store solar energy in the form of glucose molecules for periods of low energy production.
The cycle between photosynthetic plants and aerobic animals is clear just from looking at the equation describing photosynthesis. The utility of the products of photosynthesis lies in the fact that they are the reactants for aerobic metabolism, the method of energy production used by all animals, including humans. The products of photosynthesis have enabled the evolution of life on Earth by providing a source of high energy chemicals in a form that can be utilized in a controlled manner. Rather than depending on the unpredictable solar energy radiating from the sun, plants and animals are able to finely regulate the activity of enzymes and other biochemical processes in their cells using the products of photosynthesis.