The two main output products of photosynthesis are oxygen and sugar. Plants use energy from the sun to produce these items from water and carbon dioxide. The oxygen produced is emitted as a waste product, while the sugar is used to produce energy through cellular respiration.
Photosynthesis takes six molecules of carbon dioxide and six of water and uses sunlight energy to convert them into six molecules of oxygen and a single sugar molecule with the structure C6H12O6. The oxygen produced in this chemical reaction provides the essential ingredient for respiration by humans and other animals; photosynthesis is thus necessary for both plants and animals to survive.
Photosynthesis occurs inside plant cells in a material called chlorophyll. This substance is what gives plants their green color. Chlorophyll absorbs energy from sunlight, particularly from the red and blue wavelengths; the green wavelengths are reflected away from the chlorophyll, giving a green appearance. This energy is required to make the chemical bonds that allow photosynthesis to take place.
In order to achieve photosynthesis, a plant must have access to water, sunlight and carbon dioxide. However, different environments provide different access to these resources. For example, desert plants have very limited access to water. As a result, plants have evolved to maximize their local resources. Broad leaves provide massive surface area to volume ratios, ensuring maximum access to sunlight. Similarly, some plants have extensive root systems to provide greater access to water.