What Is Photosynthesis?

Photosynthesis is a chemical process that takes place in plant cells. It is the opposite of the process of cell respiration.

Cell respiration breaks down sugar molecules such as glucose to give off energy and it produces water and carbon dioxide as waste products. Photosynthesis uses energy trapped from sunlight to put water and carbon dioxide together in a series of biochemical reactions to form the sugar glucose.

Photosynthesis occurs in many tiny steps but generally has two phases. The first phase is dependent on light levels ~ it can only occur when the plant cell is in sunlight. When the light hits the leaf it passes into the cells and reaches the chloroplast. Each chloroplast has tiny stacks of membranes called grana that consist of thylakoids that contain light-trapping molecules. They convert the light energy to chemical energy and pass it to other chemicals in the chloroplast.

It is then used to drive a whole series of chemical reactions that do not need light ~ they can just as easily happen in the dark. At the end of these reactions, sugars such as glucose have been built up using carbon dioxide and water as raw materials.

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