Photosynthesis

Photosynthesisphotosynthesis: photosynthesis is the process where green plants use water and carbon dioxide and sunlight to produce carbohydrates (stored energy) and release oxygen (as a by-product). is the chemical change which happens in the leaves of green plants. It is the first step towards making food - not just for plants but ultimately every animal on the planet.

During this reaction, carbon dioxide [Carbon dioxide: Waste product of aerobic exercise that is breathed out through the lungs. ] and water are converted into glucose and oxygen [oxygen: gaseous element making up about 20% of the air, which is needed by living organisms for respiration ]. The reaction requires light energy [light energy: Visible electromagnetic radiation. ], which is absorbed by a green substance called chlorophyll.

Photosynthesis takes place in leaf cells. These contain chloroplasts, which are tiny objects containing chlorophyll.

Cross-section through a leaf cell

Here is the equation for photosynthesis:

carbon dioxide + water (+ light energy)    →    glucose + oxygen

'Light energy' is shown in brackets because it is not a substance. You will also see the equation written like this:

Plants absorb water through their roots, and carbon dioxide through their leaves. Some glucose is used for respiration, while some is converted into insoluble starch [starch: a type of carbohydrate. Plants can turn the glucose produced in photosynthesis into starch for storage, and turn it back into glucose when it is needed for respiration. ] for storage. The stored starch can later be turned back into glucose and used in respiration. Oxygen is released as a by-product of photosynthesis.