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Paper 1
Bioenergetics
Both
Know the word equation and limiting factors.
Key Facts
- Chlorophyll absorbs light for photosynthesis.
- Respiration happens in mitochondria.
- Light intensity is the limiting factor at low light.
- Anaerobic respiration in yeast produces ethanol and carbon dioxide.
Key Equations
carbon dioxide + water -> glucose + oxygen
glucose + oxygen -> carbon dioxide + water
glucose -> lactic acid
glucose -> ethanol + carbon dioxide
Topics Covered
Photosynthesis
What you need to know
- •Photosynthesis uses light to convert carbon dioxide and water into glucose.
- •Limiting factors: light intensity, CO2 concentration, temperature.
Exam Tips
- State the equation before describing limiting factors.
Respiration
What you need to know
- •Aerobic respiration releases energy using oxygen.
- •Anaerobic respiration produces lactic acid and less energy.
Exam Tips
- Name the reactants and products clearly.
Rates and Practical Skills
What you need to know
- •Rate of photosynthesis can be measured by oxygen production.
- •Temperature affects enzyme-controlled reactions.
Exam Tips
- Use rate units like cm^3 per minute or bubbles per minute.
Key Terms
Aerobic
Reactions that use oxygen.
Anaerobic
Reactions that do not use oxygen.
Limiting factor
The factor that stops the rate increasing.
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Common Exam Questions
Explain how temperature affects the rate of photosynthesis.
4 marksmediumPaper 1
Model Answer
As temperature rises, enzyme activity increases, so the rate increases up to an optimum. Above optimum, enzymes denature and the rate falls.
What examiners want to see
- ✓Mention enzyme activity.
- ✓State optimum and denaturation.
Explain why a photosynthesis rate graph levels off at high light intensity.
3 marksmediumPaper 1
Model Answer
Light is no longer limiting, so another factor like CO2 concentration limits the rate.
What examiners want to see
- ✓State light is not limiting.
- ✓Name another limiting factor.
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