GCSERevise
AQASpec 4.4.1Foundation & Higher~30 min

Photosynthesis

Biology · Topic revision workspace

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Topic overview

What you need to know

Photosynthesis is a key part of GCSE Biology. Connect structures to their functions and explain biological processes as clear causal sequences. 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (carbon dioxide + water → glucose + oxygen). Requires light energy. The green pigment found in chloroplasts that absorbs light energy for photosynthesis. A reaction that takes in energy from the surroundings. Photosynthesis is endothermic — it absorbs light energy.

Exam tip

Use precise scientific vocabulary and make each link in an explanation explicit.

Revision notes

Core ideas

Secure these ideas first. Say each definition in your own words, then connect it to the topic overview.

  • Photosynthesis Equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (carbon dioxide + water → glucose + oxygen). Requires light energy.
  • Chlorophyll: The green pigment found in chloroplasts that absorbs light energy for photosynthesis.
  • Endothermic Reaction: A reaction that takes in energy from the surroundings. Photosynthesis is endothermic — it absorbs light energy.
  • Limiting Factor: A factor that restricts the rate of photosynthesis when in short supply: light intensity, CO₂ concentration, or temperature.

Revision notes

Apply it in the exam

The exam will rarely ask for an isolated definition. Practise selecting the right idea and using it as part of a complete explanation or method.

  • Light Intensity: As light intensity increases, the rate of photosynthesis increases — up to a point where another factor becomes limiting.
  • Carbon Dioxide Concentration: Increasing CO₂ concentration increases the rate of photosynthesis until another factor becomes limiting.
  • Inverse Square Law (Light): Light intensity is inversely proportional to the square of the distance from the light source: I ∝ 1/d².
  • Uses of Glucose: Plants use glucose for: respiration, making cellulose (cell walls), making amino acids (with nitrates), making starch (storage), making lipids (oils).

Core knowledge

Key facts for Photosynthesis

1

Photosynthesis Equation

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (carbon dioxide + water → glucose + oxygen). Requires light energy.

2

Chlorophyll

The green pigment found in chloroplasts that absorbs light energy for photosynthesis.

3

Endothermic Reaction

A reaction that takes in energy from the surroundings. Photosynthesis is endothermic — it absorbs light energy.

4

Limiting Factor

A factor that restricts the rate of photosynthesis when in short supply: light intensity, CO₂ concentration, or temperature.

5

Light Intensity

As light intensity increases, the rate of photosynthesis increases — up to a point where another factor becomes limiting.

6

Carbon Dioxide Concentration

Increasing CO₂ concentration increases the rate of photosynthesis until another factor becomes limiting.

7

Inverse Square Law (Light)

Light intensity is inversely proportional to the square of the distance from the light source: I ∝ 1/d².

8

Uses of Glucose

Plants use glucose for: respiration, making cellulose (cell walls), making amino acids (with nitrates), making starch (storage), making lipids (oils).

Active recall

Close the notes and answer these

  1. 1.Without looking, explain photosynthesis equation and give one example or consequence.
  2. 2.Without looking, explain chlorophyll and give one example or consequence.
  3. 3.Without looking, explain endothermic reaction and give one example or consequence.
  4. 4.Without looking, explain limiting factor and give one example or consequence.

Content reviewed 23 July 2026 against the current linked specification.

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