The Process of Photosynthesis (Edexcel IGCSE Biology)
Revision Note
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Photosynthesis Theory
Photosynthesis is an endothermic reaction in which energy from sunlight is transferred to the chloroplasts in green plants
Energy from sunlight is absorbed by chlorophyll, a green pigment found inside chloroplasts
Green plants use this energy to 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
Photosynthesis can be defined as the process by which plants manufacture carbohydrates from raw materials using energy from light
Plants are
Autotrophs – they can make complex molecules (glucose) from simple molecules (carbon dioxide and water)
Producers – they can make their own food and so are the first organism at the start of all food chains
The products of photosynthesis
Plants use the glucose they make as a source of energy in respiration
They can also use it to
Produce starch for storage
Synthesise lipids for an energy source in seeds
To form cellulose to make cell walls
Produce amino acids (used to make proteins) when combined with nitrogen and other mineral ions absorbed by roots
Once the carbon from carbon dioxide is taken into the plant and converted to glucose in photosynthesis, it can then be converted and used in many different types of biological molecule.
Examiner Tips and Tricks
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.
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Photosynthesis Equations
Photosynthesis can be summarised in a word equation as shown below:
Word equation for photosynthesis
Sources of the reactants and uses of the products of photosynthesis
This equation can also be shown as a balanced chemical symbol equation
Six carbon dioxide molecules combine with six water molecules to make one glucose molecule and six oxygen molecules
The balanced symbol equation for photosynthesis
Examiner Tips and Tricks
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.
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