Practise Rate of photosynthesis. 19 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Required practical:Photosynthesis (method, variables and exam tips)
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Pondweed releases bubbles of gas when it photosynthesises. Name the gas.
Oxygen
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy6 marks
The rate of photosynthesis in a plant can be limited by several factors.
(a) Give three factors that affect the rate of photosynthesis.[3]
(b) What is meant by a limiting factor?[1]
(c) Pondweed releases bubbles of gas when it photosynthesises. Name the gas.[1]
(d) Suggest how a student could measure the rate of photosynthesis of a piece of pondweed.[1]
Show the answer and mark scheme
(a)
temperature
light intensity
carbon dioxide concentration
amount of chlorophyll
(b)
the factor in shortest supply, which stops the rate of photosynthesis increasing
(c)Answer: Oxygen
oxygen
(d)
count the number of bubbles (of oxygen) produced per minute / measure the volume of gas produced per minute
Question 2Medium5 marks
Instead of counting bubbles, a student used a data logger with an oxygen probe placed in the water next to some pondweed, to measure the concentration of dissolved oxygen every 10 seconds.
(a) Suggest two advantages of using a data logger with an oxygen probe, rather than counting bubbles, to measure the rate of photosynthesis.[2]
(b) Explain why some of the oxygen produced by the pondweed might not be detected by the oxygen probe.[2]
(c) Suggest one reason the student should let the apparatus settle for a short time after changing the light intensity, before taking readings.[1]
Show the answer and mark scheme
(a)
it gives a continuous, more precise numerical measurement of the oxygen produced, rather than relying on counting bubbles of varying size
it can take readings automatically and very frequently, which would be difficult to do accurately by counting bubbles by eye
results are stored and processed by a computer, reducing recording errors
(b)
some oxygen may escape from the water as bubbles rather than dissolving
some of the oxygen produced may be used by the plant itself for respiration
(c)
to allow the rate of photosynthesis, and the dissolved oxygen concentration, to reach a new steady rate at the new light intensity
Question 3Hard7 marks
The light intensity from a lamp is inversely proportional to the square of the distance from the lamp: \(\text{light intensity} \propto \dfrac{1}{d^2}\)
(a) A lamp is moved from 10 cm to 20 cm away from some pondweed. Calculate the light intensity at 20 cm as a fraction of the light intensity at 10 cm.[1]
(b) The relative light intensity at a distance d can be calculated using: \(\text{relative light intensity} = \dfrac{1}{d^2}\) Calculate the relative light intensity at 25 cm. Give your answer in standard form.[2]
(c) With the lamp 10 cm from the pondweed, the rate of photosynthesis was 60 bubbles per minute. Assume the rate of photosynthesis is directly proportional to light intensity. Predict the rate at 30 cm.[2]
(d) The student actually counted 12 bubbles per minute at 30 cm. Suggest two reasons why this was higher than predicted.[2]
Show the answer and mark scheme
(a)Answer: ¼ (0.25)
¼ / 0.25
(b)Answer: 1.6 × 10−3 arbitrary units
1 ÷ 252 = 1 ÷ 625
1.6 × 10−3
(c)Answer: 6.7 bubbles per minute
light intensity at 30 cm is 1/9 of that at 10 cm / 60 × (10 ÷ 30)2
6.7 (bubbles per minute)
(d)
at 10 cm another factor (e.g. carbon dioxide / temperature) was limiting, so the rate at 10 cm was lower than it would be if only light were limiting
light from other sources (e.g. room lights / a window) also reached the pondweed
the rate of photosynthesis is not directly proportional to light intensity at high light intensity