AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Photosynthetic reaction: Photosynthesis is represented by the equation:
Photosynthesis is the process by which plants, algae and some bacteria use light energy to convert carbon dioxide and water into glucose and oxygen.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 1 of 5
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Photosynthesis is the process by which plants, algae and some bacteria use light energy to convert carbon dioxide and water into glucose and oxygen. The overall change is summarised by the word equation carbon dioxide + water → glucose + oxygen, and by the balanced symbol equation 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. The reaction is endothermic because it transfers energy from the environment as light is absorbed. It occurs mainly in the chloroplasts of leaf cells, where chlorophyll absorbs light. The glucose produced is used for respiration, converted to starch for storage, or used to make cellulose, amino acids and lipids. Oxygen is released as a by-product.
What earns the marks
- States the word equation: carbon dioxide + water → glucose + oxygen.
- Writes the balanced symbol equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
- Identifies light as the energy source absorbed by chlorophyll in chloroplasts.
- Explains that photosynthesis is endothermic and stores energy in glucose.
- Names glucose and oxygen as the products and carbon dioxide and water as the reactants.
- Links the process to its role in supplying glucose for respiration and growth and releasing oxygen.
Common mistakes and how to put them right
Writing the word equation with oxygen and glucose as reactants.
Put it right: Carbon dioxide and water are the reactants, glucose and oxygen are the products.
Omitting the 6 in front of CO₂, H₂O or O₂ in the symbol equation.
Put it right: Balance each element so that 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
Stating that photosynthesis is exothermic.
Put it right: It is endothermic because it takes in light energy and stores it in glucose.
Exam tips
- Learn both the word equation and the balanced symbol equation, and practise writing them from memory.
- When asked to explain the equation, name the energy source and the location of the process, not just the reactants and products.
- Check that every chemical formula in the symbol equation is balanced before moving on to the next part of the question.
Try the lesson
The start of the Photosynthetic reaction: Photosynthesis is represented by the equation: lesson, made from checked teaching notes for this specification point.
Have a go first
Which word equation represents photosynthesis?
Listen
Photosynthesis is the process by which plants, algae and some bacteria use light energy to convert carbon dioxide and water into glucose and oxygen. The overall change is summarised by the word equation carbon dioxide + water → glucose + oxygen, and by the balanced symbol equation 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. The reaction is endothermic because it transfers energy from the environment as light is absorbed. It occurs mainly in the chloroplasts of leaf cells, where chlorophyll absorbs light. The glucose produced is used for respiration, converted to starch for storage, or used to make cellulose, amino acids and lipids. Oxygen is released as a by-product. A strong answer earns marks for these points. States the word equation: carbon dioxide + water → glucose + oxygen. Writes the balanced symbol equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Identifies light as the energy source absorbed by chlorophyll in chloroplasts. Explains that photosynthesis is endothermic and stores energy in glucose. A common slip: Writing the word equation with oxygen and glucose as reactants. Instead, carbon dioxide and water are the reactants, glucose and oxygen are the products. Exam tip: Learn both the word equation and the balanced symbol equation, and practise writing them from memory.
See it
Key words
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Photosynthesis
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Endothermic
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Reactants
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Products
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See every definition
- Photosynthesis
- The process by which plants, algae and some bacteria use light energy to convert carbon dioxide and water into glucose and oxygen.
- Endothermic
- Describes the reaction that transfers energy from the environment as light is absorbed and stores energy in glucose.
- Reactants
- Carbon dioxide and water, which are converted into glucose and oxygen.
- Products
- Glucose and oxygen, formed when carbon dioxide and water are converted using light energy.
Label the diagram
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