GCSE Combined Science revision · Biology: cells, organisation and disease

Photosynthesis

The idea

Photosynthesis is an endothermic reaction in chloroplasts: carbon dioxide + water → glucose + oxygen, using energy from light. Its rate is limited by temperature, light intensity, carbon dioxide concentration and the amount of chlorophyll. Plants use glucose for respiration, to make starch for storage, cellulose for cell walls, amino acids for proteins (with nitrate ions) and fats or oils.

Write the word equation.
Identify the limiting factor in a graph.
Name the use of the glucose.

Watch out Photosynthesis is endothermic: it takes in energy from light.

See it worked

Worked example

A plant's rate of photosynthesis does not rise when the light gets brighter. Suggest why.

Another factor is limiting the rate.
This could be carbon dioxide concentration or temperature.

Answer Another factor, such as carbon dioxide or temperature, is limiting

Your turn

Question 1Calculator allowed1 mark

What are the products of photosynthesis?

Question 2Calculator allowed1 mark

Plants combine glucose with nitrate ions to make:

Question 3Calculator allowed2 marks

A pondweed gives off 36 bubbles of oxygen in 3 minutes. What is the rate in bubbles per minute?

In past papers

43 official questions in 33 papers since 2018. The latest:

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