Biology›Rate of Photosynthesis — Required Practical
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B4.3 · RPA6Paper 1
Rate of Photosynthesis — Required Practical
Investigating the effect of light intensity on photosynthesis rate. Required Practical 6 — the lamp/pondweed experiment appears regularly as a 6-mark method or evaluate question.
FreeScienceLessons · AQA BiologyPhotosynthesis — rate and limiting factors
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Key facts
The pondweed experiment — method
Place pondweed (e.g. Elodea) in a beaker of water with sodium hydrogen carbonate (provides CO₂)
Shine a lamp at the pondweed from a measured distance
Count oxygen bubbles per minute — this measures photosynthesis rate
Move the lamp to different distances and repeat — each distance gives a different light intensity
Wait for the rate to stabilise before counting
Repeat at each distance and calculate a mean bubble count
Variables — fill in the table
Variable
Detail
Independent variable
Dependent variable
Control variables
Light intensity formula — fill in the table
Aspect
Detail
Relationship
Effect of doubling distance
Law
Graph
Exam questions — 3 questions · 10 marks total
⚡ This module includes extended questions (4–6 marks). These are where most marks are lost. Read the hint carefully. Write in linked sentences. The AI will identify exactly which mark scheme points you missed.
1 markVariable identificationAQA 8461 style
In the pondweed experiment, what is the dependent variable?
A The distance of the lamp from the pondweed
B The temperature of the water
C The number of oxygen bubbles produced per minute
D The concentration of sodium hydrogen carbonate
6 marksDescribe the methodAQA 8461 RPA6 style
A student investigates how light intensity affects the rate of photosynthesis using pondweed. Describe a method the student could use and explain how they would make the results valid and reliable. (6 marks)
Hint: Cover: setup (pondweed, lamp, sodium hydrogen carbonate), measuring rate (bubbles per minute), changing light intensity (distance), repeating for reliability, and controlling variables.
+60 XP
3 marksEvaluate resultsAQA 8461 style
A student finds that increasing light intensity beyond a certain point does not increase the photosynthesis rate. Suggest why, and state what factor is now limiting the rate. (3 marks)
Hint: Think about limiting factors — when light is no longer limiting, what else could be?