The Calvin cycle of photosynthesis begins after light energy is transformed into chemical energy by the cells of plants. The adenosine triphosphate, or ATP, molecules created power the Calvin cycle. The Calvin cycle uses the energy to create carbohydrates from water and carbon dioxide.
The Calvin cycle is the main way the energy created during photosynthesis is used. The carbohydrates it generates are both the main energy storage molecules and the main structural components of plants. The Calvin cycle only creates simple sugars by itself, but more complex carbohydrates such as starches and cellulose are constructed from those simple sugars in other processes.
Photosynthesis takes place in the chloroplasts, special organelles in plant cells and algae. To use the light energy from the sun, the chloroplasts have molecules known as chlorophyll. These molecules are large protein structures with a magnesium atom in the middle. The light energy causes the magnesium atoms to release electrons, which then power the creation of ATP. Not all the reactions are direct. Other molecules like beta carotene can absorb light energy and pass the energy to the chlorophyll molecule. These other molecules absorb different colors of light than chlorophyll, so they help the plant cells be more efficient.