Edexcel IGCSEBiologyGeneral Applications7 Marks

A student investigated the effect of light intensity on the rate of photosynthesis in an aquatic plant.

(a)(i)State two factors, other than light intensity, that would affect the rate of photosynthesis.[2]
(a)(ii)Explain why these factors need to be kept constant during the investigation.[2]
(b)The student measured the rate of photosynthesis by counting the number of gas bubbles produced per minute. Identify the gas being produced and describe a simple chemical test to confirm its identity.[3]

Mark scheme

Marking points from the official mark scheme. The mark or mark type is shown in brackets.

M1 for carbon dioxide concentration.
A1 for temperature. (Max 2)
M1 for to ensure only light intensity affects the rate / ensure a fair test.
A1 for so that any change in the rate of photosynthesis is due to light intensity only / to prevent other factors from becoming limiting factors.
M1 for oxygen.
A1 for 'relights a glowing splint' / 'splint glows brighter'.
A1 for description of method: insert glowing splint into the test tube / near the gas bubbles.

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