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Check your answer after each question. Use a calculator where needed.
Enzymes · photosynthesis · practical data
Rates and graph gradients
Practise mean rates, reciprocal time and tangent gradients with enzyme and photosynthesis contexts. Use original labelled graphs and worked solutions.
Method and worked examples ↓Learn the method
How to approach these questions
- Use two readings to find the change in quantity and the change in time.
- Divide the change on the vertical axis by the change on the horizontal axis.
- For an instantaneous rate, use two well-separated points on the tangent, which need not be recorded data points.
- Include the rate unit. If a fixed endpoint is used, 1/time can be a proxy for rate; it is not itself a volume per second.
Worked examples
Oxygen volume rises from 4 cm³ at 10 s to 22 cm³ at 70 s. Find the mean rate.
Change in volume = 22 − 4 = 18 cm³. Change in time = 70 − 10 = 60 s. Rate = 18 ÷ 60 = 0.30 cm³ s⁻¹.
A tangent passes through (20 s, 8 cm³) and (80 s, 26 cm³). Find its gradient.
Gradient = (26 − 8) ÷ (80 − 20) = 0.30 cm³ s⁻¹. Use the tangent coordinates, rather than joining the first and last points on the curve.
Keep practising
Topic map and study list · Practical data guides · Active recall decks
Course resources
AQA A-level Biology · OCR A A-level Biology · Textbook answers
Skill coverage follows the common A-level science subject content. Check your board’s current requirements: AQA 7402 and OCR A H420.