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A Level Biology 2023 Paper 3 past paper and mark scheme 2023
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A Level Biology Paper 3 past paper and mark scheme 2023 (Mock revision)
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Name: ________________________Paper 3
Exam questions based on the 2023
Class: ________________________
topic list
Date: ________________________
Time: 139 minutes
Marks: 108 marks
Comments: Essay not included
Page 1 of 39
,Q1.
Heat stress is a condition that often occurs in plants exposed to high temperatures for a
prolonged period of time. Heat stress is a major factor in limiting the rate of
photosynthesis.
(a) Heat stress decreases the light-dependent reaction of photosynthesis.
Explain why this leads to a decrease in the light-independent reaction.
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(2)
(b) Another effect of heat stress is a decrease in the activity of the enzyme rubisco. A
decrease in the activity of an enzyme means that the rate of the reaction it catalyses
becomes slower.
A decrease in the activity of the enzyme rubisco would limit the rate of
photosynthesis.
Explain why.
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(2)
(c) Where precisely is rubisco found in a cell?
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(1)
Scientists investigated the effect of temperature on the activity of two enzymes isolated
from the leaf cells of cotton plants.
• Rubisco
• Rubisco activase – an enzyme that activates rubisco
Figure 1 and Figure 2 show their results.
Page 2 of 39
, (d) The scientists concluded that heat stress reduces the activity of rubisco in plant
leaves by affecting rubisco activase.
Use all the information to evaluate their conclusion.
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(4)
(Total 9 marks)
Q2.
(a) Where precisely in a cell does the Calvin cycle take place?
___________________________________________________________________
(1)
(b) A scientist investigated the effect of changing the carbon dioxide concentration on
Page 3 of 39
, the amounts of glycerate-3-phosphate (GP) and ribulose bisphosphate (RuBP) in
photosynthesising cells.
The graph shows the results obtained when the carbon dioxide concentration was
reduced.
(i) Explain the decrease in the amount of GP after the carbon dioxide
concentration was reduced.
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(1)
(ii) The scientist carried out a similar experiment but increased the carbon
dioxide concentration from 1% to 2%. The relative amounts of GP and RuBP
remained the same.
Suggest two reasons why.
1. ____________________________________________________________
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2. ____________________________________________________________
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(2)
(c) Some bacteria use hydrogen sulfide, H2S, to produce organic compounds.
The hydrogen sulfide has a similar role to that of water in photosynthesis.
A simple equation for this process in bacteria is shown below:
hydrogen sulfide + carbon dioxide → glucose + sulfur + water
Suggest what the hydrogen sulfide is used for in these bacteria.
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Page 4 of 39
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