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Photosynthesis is the process by which plants and other things make food. It is a chemical process that uses sunlight to turn carbon dioxide into sugars the plant cells can use as energy. As well as plants, many kinds of algae, protists and bacteria use it to get food. Photosynthesis is very important for life on Earth, as most plants either directly or indirectly depend on it. The exception are certain organisms that directly get their energy from chemical reactions; these organisms are called chemoautotrophs.

The usual process of Photosynthesis goes like this:

Carbon Dioxide + Water + Light photons (from the Sun or any other light source) → Oxygen + Glucose (→ Starch, as plants cannot store glucose)

How it happens

Diagram of a chloroplast

Light energy from the sun is used to split water molecules (photolysis). The sunlight hits chloroplasts in the plant, causing an enzyme to break apart the water. Water, when broken, makes oxygen, hydrogen, and electrons. The hydrogen, along with the electrons energized by light, turn NADP into Nicotinamide Adenine Dinucleotide Phosphate which will be used in the chemical reactions. Oxygen diffuses out of the plant as a waste product of photosynthesis, and ATP is synthesized from Adenosine Diphosphate and inorganic phosphate. This all happens inside the chloroplasts.


Today, the average rate of energy capture by photosynthesis globally is approximately 130 terawatts, which is about six times larger than the current power used by human civilization. Photosynthetic organisms also convert around 100–115 thousand million metric tonnes of carbon into biomass per year.