A student investigates the effect of light intensity on the rate of photosynthesis using pondweed. Which variable should be kept constant to make the investigation a fair test?

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Question

A student investigates the effect of light intensity on the rate of photosynthesis using pondweed. Which variable should be kept constant to make the investigation a fair test?

Accepted Answer

The temperature of the water surrounding the pondweed — Temperature must be kept constant because it is a confounding variable — it affects enzyme activity and therefore the rate of photosynthesis independently of light intensity. Distance is the independent variable being changed, so it cannot be a control variable. Bubble count is the dependent variable being measured. Colour of light would only be relevant if wavelength were the independent variable.

Answer

The distance of the lamp from the pondweed

Answer

The number of bubbles counted per minute

Answer

The temperature of the water surrounding the pondweed

Answer

The colour of light used in each repeat

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