Question
Describe how you could investigate the effect of light intensity on the rate of photosynthesis using pondweed (Elodea or Cabomba).
[5 marks]
Mark scheme — any five from:
- Place a piece of pondweed in a beaker of sodium hydrogen carbonate solution (provides CO₂) (B1)
- Place a lamp at a measured distance from the beaker (B1)
- Allow the plant to acclimatise for 5 minutes before counting (B1)
- Count the number of bubbles produced per minute (or measure volume of gas collected) (B1)
- Repeat at different lamp-to-beaker distances (B1)
- Control variables: same pondweed length, same temperature (water bath), same NaHCO₃ concentration (B1)
- Plot a graph of rate vs distance OR rate vs 1/d² (B1)
5 marks · take your time before peeking.
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Generated by TopMyGrade AI · cross-check official sources before relying on the mark-scheme phrasing.