Y10 Biology - rp - effect of light on photosynthesis

1. Independent variable

Light intensity changed by altering lamp distance

2. Dependent variable

Number of bubbles per minute showing oxygen production

3. Control variable

Temperature kept constant to avoid enzyme rate changes

4. Control variable

CO₂ concentration kept constant using sodium hydrogencarbonate

5. Control variable

Same pondweed used to keep photosynthesis rate consistent

6. Reason for sodium hydrogencarbonate

Prevents CO₂ becoming limiting

7. Reason for changing lamp distance

Provides measurable changes in light intensity

8. Reason for counting bubbles

Indicates rate of photosynthesis via oxygen output

9. Reason for acclimatisation

Allows pondweed to reach steady photosynthesis rate

10. Hazard

Hot lamp

11. Risk

Burns from touching lamp

12. Precaution

Keep lamp away from water to avoid electric shock

13. Hazard

Water near electrical equipment

14. Risk

Electric shock

15. Precaution

Keep wires and plug sockets dry and away from beaker

16. Step 1

Place pondweed (Elodea) in beaker of water

17. Step 2

Add sodium hydrogencarbonate to ensure CO₂ availability

18. Step 3

Position lamp at a set starting distance from pondweed

19. Step 4

Allow pondweed to acclimatise for a few minutes

20. Step 5

Count bubbles released for 1 minute

21. Step 6

Record results in a table

22. Step 7

Move lamp further away to reduce light intensity

23. Step 8

Repeat bubble count at each distance for reliability

24. Step 9

Plot graph of rate of photosynthesis against 1/distance²

25. Reason for 1/distance² graph

Light intensity is inversely proportional to distance