- Green plants make the carbohydrate glucose from the raw materials carbon dioxide and water
- At the same time oxygen is made and released as a waste product
- The reaction requires energy which is obtained by the pigment chlorophyll trapping light from the Sun
- So photosynthesis can be defined as the process by which plants manufacture carbohydrates from raw materials using energy from light
- It can be summed up in the following equation:
If asked for the raw materials required for photosynthesis, the answer is carbon dioxide and water.
Although required for the reaction to take place, light energy is not a substance and therefore cannot be a raw material.
- The balanced chemical equation for photosynthesis is:
- The light energy is converted into chemical energy in the bonds holding the atoms in the glucose molecules together
The photosynthesis equation is the exact reverse of the aerobic respiration equation so if you have learned one you also know the other one!
You will usually get more marks for providing the balanced chemical equation than the word equation.
- Plants use the glucose they make as a source of energy in respiration
- They can also convert it into starch for storage, into lipids for an energy source in seeds, into cellulose to make cell walls or into amino acids (used to make proteins) when combined with nitrogen and other mineral ions absorbed by roots