Photosynthesis – Complete GCSE Biology Notes
Topic Overview
Photosynthesis is the process by which green plants make their own food using light energy, carbon dioxide, and water. This topic is very important in GCSE Biology and commonly appears as 4–6 mark questions in exams.
Key Concept Notes
- Photosynthesis occurs in the chloroplasts of plant cells.
- Chloroplasts contain chlorophyll which absorbs light energy.
- Raw materials needed: carbon dioxide (from air) and water (from roots).
- Energy from light is used to convert CO₂ and H₂O into glucose.
- Oxygen is released as a waste product.
- Word Equation: Carbon dioxide + Water → Glucose + Oxygen
- Balanced Equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Uses of Glucose in Plants
- Used for respiration.
- Stored as starch.
- Used to make cellulose for cell walls.
- Used to make proteins and fats.
Diagrams
Diagram showing photosynthesis in a leaf
Chloroplast structure – site of photosynthesis
6-Mark Exam Answer – Example 1
Question: Explain how light affects the rate of photosynthesis. (6 marks)
Model Answer:
- Photosynthesis requires light energy absorbed by chlorophyll.
- Light provides energy to convert carbon dioxide and water into glucose.
- At low light intensity, the rate of photosynthesis is low.
- As light intensity increases, the rate of photosynthesis increases.
- Eventually the rate levels off because another factor becomes limiting (CO₂ or temperature).
- Without light, photosynthesis cannot occur.
6-Mark Exam Answer – Example 2
Question: Describe the process of photosynthesis. (6 marks)
- Photosynthesis takes place in the chloroplasts.
- Chlorophyll absorbs light energy.
- Carbon dioxide enters the leaf through stomata.
- Water is absorbed by the roots and transported to the leaves.
- Light energy is used to make glucose.
- Oxygen is released into the air.
Exam Tips
- Always mention chlorophyll and light energy.
- Write answers in logical order.
- Use keywords from the question.
- For 6 marks, aim for 6 clear points.
- Include diagrams where possible for extra clarity.