Photosynthesis
Recap Photosynthesis for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Learn both the word and symbol equations, and remember that photosynthesis is endothermic — it transfers energy in from the environment.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Photosynthesis is the process by which plants and algae make glucose using energy transferred from light. It is an endothermic reaction, meaning energy is taken in.
The word equation is carbon dioxide + water → glucose + oxygen, with light and chlorophyll required. The symbol equation is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
It takes place in the chloroplasts, which contain the green pigment chlorophyll. Chlorophyll absorbs the light energy that drives the reaction, which is why leaves are green and why plants grown in the dark cannot survive once their stored glucose runs out.
Revision notes
The reaction
Carbon dioxide + water → glucose + oxygen, requiring light and chlorophyll.
In symbols: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. It is endothermic because energy is transferred from the environment, in this case from light.
Where it happens
Photosynthesis takes place in the chloroplasts, which contain chlorophyll.
Chlorophyll absorbs light energy. Most chloroplasts are in the palisade mesophyll near the top of the leaf, where the most light reaches.
Getting the raw materials
Carbon dioxide diffuses into the leaf through the stomata. Water is absorbed by the roots and carried up in the xylem.
Oxygen is released as a waste product and diffuses out through the stomata, and glucose is used for respiration or converted for storage.
Key points
- Photosynthesis makes glucose using light energy.
- It is an endothermic reaction.
- Carbon dioxide + water → glucose + oxygen.
- It takes place in chloroplasts containing chlorophyll.
- Carbon dioxide enters through the stomata.
- Water is absorbed by the roots and carried in the xylem.
Worked examples
Example 1
Write the word equation for photosynthesis. [2 marks]
Model answer
Carbon dioxide + water → glucose + oxygen. Correct reactants, carbon dioxide and water (1 mark). Correct products, glucose and oxygen (1 mark).
Example 2
Explain why photosynthesis is described as an endothermic reaction. [2 marks]
Model answer
Energy is transferred from the environment into the reaction (1 mark), in this case light energy absorbed by chlorophyll (1 mark).
Example 3
Explain why a plant kept in complete darkness will eventually die. [3 marks]
Model answer
Without light the plant cannot carry out photosynthesis (1 mark), so it cannot make glucose (1 mark). Once its stored glucose is used up in respiration there is no source of energy, so the plant dies (1 mark).
Common mistakes
Saying photosynthesis produces energy.
It transfers energy from light into chemical energy stored in glucose. Energy is not created.
Calling photosynthesis exothermic.
It is endothermic — energy is taken in from the surroundings.
Forgetting that light and chlorophyll are required.
They are written above and below the arrow, and are often worth a mark.
Saying plants only respire at night.
Plants respire continuously; photosynthesis simply exceeds respiration during the day.
Exam tips
- Learn both the word and symbol equations.
- Say endothermic and explain that energy is taken in.
- Name chlorophyll as the pigment absorbing light.
- Remember plants respire all the time, not just at night.
Key terms
- Photosynthesis
- The process making glucose from carbon dioxide and water using light.
- Endothermic
- Taking in energy from the surroundings.
- Chlorophyll
- The green pigment that absorbs light energy.
- Chloroplast
- The organelle where photosynthesis takes place.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.