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AQA GCSE · Question 03.1 · Bioenergetics
A scientist investigated the rate of photosynthesis of one type of tomato plant. The tomato plants were grown in a greenhouse. Table 2 shows the results.
Give two control variables the scientist should have used in the investigation.
A scientist investigated the rate of photosynthesis of one type of tomato plant. The tomato plants were grown in a greenhouse. Table 2 shows the results.
Give two control variables the scientist should have used in the investigation.
How to approach this question
1. Identify the independent variable (what the scientist changed): concentration of carbon dioxide.
2. Identify the dependent variable (what the scientist measured): rate of photosynthesis.
3. A control variable is anything else that could affect the dependent variable. Think about the requirements for photosynthesis. What factors, other than CO2 concentration, affect the rate of photosynthesis?
4. List two of these factors. They must be kept constant to ensure a fair test.
Full Answer
In any scientific investigation, it is crucial to keep all variables constant except for the independent and dependent variables. This ensures that any observed change in the dependent variable is due to the change in the independent variable, making it a fair test.
The rate of photosynthesis is affected by several limiting factors:
- **Carbon dioxide concentration** (the independent variable in this experiment).
- **Light intensity:** More light (up to a point) increases the rate. This must be kept the same for all plants.
- **Temperature:** Photosynthesis is controlled by enzymes, which have an optimal temperature. The temperature must be kept constant.
- **Amount of water:** Water is a reactant in photosynthesis. All plants should receive the same amount of water.
Therefore, light intensity and temperature are two key control variables.
Common mistakes
✗ Naming the independent variable (CO2 concentration) or dependent variable (rate of photosynthesis).\n✗ Giving vague answers like "amount of light" instead of "light intensity".\n✗ Listing factors that would not affect photosynthesis, like "amount of soil".
Practice the full AQA GCSE Biology Foundation Tier Paper 1
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