1. Which of the following is not a role of an intracellular membrane?
A cell to cell signalling
B partially permeable barrier
C site of chemical reactions
D transport of substances across the membrane
Your answer
[1]
2(a). Biological processes can be investigated using models.
The effect of cell size on diffusion can be investigated using cubes of agar jelly to represent cells of different sizes.
A student used cubes of agar jelly containing universal indicator, which changes colour at different pH.
● Five different sizes of cubes were cut from a larger block using a scalpel.
● Cubes were placed in a beaker containing hydrochloric acid (enough to cover the cubes) and a stopwatch was started.
● After 2 minutes the cubes were removed, rinsed with distilled water and blotted dry.
● Acid absorbed at the outside continued diffusing towards the centre of the blocks.
● The time taken for the blocks to turn entirely red was recorded.
The results are shown in Table 22.1 on the insert.
What was the role of the universal indicator in this experiment?
[1]
(b).
i. In the space provided, plot a graph of mean time taken to turn red against surface area to volume ratio.
[
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, ii. Describe the pattern shown by your graph.
[1]
iii. An identical procedure was carried out on a cube of unknown size. This cube turned red after 21.5 min.
Use your graph to estimate the surface area to volume ratio of this unknown cube.
Answer........................................................... [
iv. Suggest how the original procedure could be modified in order to improve the accuracy of your answer to part (iii).
[1]
(c). Use the data in Table 22.1, on the insert, to calculate the rate of diffusion of acid in Cube C from the outer surface to the centre of
the cube.
Answer........................................................... [3]
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, (d).
i. Explain which of the mean values, A–E, is likely to be the least accurate. You should process data from the table to support your
answer.
[2]
ii. Identify one limitation in the practical procedure that may have caused the results to be inaccurate and explain which cube's
results are most likely to have been affected by this limitation.
Limitation
Is more likely to affect cube ….. because
[
(e). The procedure described above involved the use of model cells. Hydrogen ions from the acid were able to travel freely to the centre
of the agar jelly cubes.
The rate of movement of molecules from the plasma membrane towards the centre of living cells is often greater than that seen in the
procedure the student carried out even if the cells are kept at the same temperature.
Suggest a reason for this observation.
[1]
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A cell to cell signalling
B partially permeable barrier
C site of chemical reactions
D transport of substances across the membrane
Your answer
[1]
2(a). Biological processes can be investigated using models.
The effect of cell size on diffusion can be investigated using cubes of agar jelly to represent cells of different sizes.
A student used cubes of agar jelly containing universal indicator, which changes colour at different pH.
● Five different sizes of cubes were cut from a larger block using a scalpel.
● Cubes were placed in a beaker containing hydrochloric acid (enough to cover the cubes) and a stopwatch was started.
● After 2 minutes the cubes were removed, rinsed with distilled water and blotted dry.
● Acid absorbed at the outside continued diffusing towards the centre of the blocks.
● The time taken for the blocks to turn entirely red was recorded.
The results are shown in Table 22.1 on the insert.
What was the role of the universal indicator in this experiment?
[1]
(b).
i. In the space provided, plot a graph of mean time taken to turn red against surface area to volume ratio.
[
© OCR 2022. You may photocopy
Page 1 of 25 Created in ExamBuilder
this page.
, ii. Describe the pattern shown by your graph.
[1]
iii. An identical procedure was carried out on a cube of unknown size. This cube turned red after 21.5 min.
Use your graph to estimate the surface area to volume ratio of this unknown cube.
Answer........................................................... [
iv. Suggest how the original procedure could be modified in order to improve the accuracy of your answer to part (iii).
[1]
(c). Use the data in Table 22.1, on the insert, to calculate the rate of diffusion of acid in Cube C from the outer surface to the centre of
the cube.
Answer........................................................... [3]
© OCR 2022. You may photocopy
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this page.
, (d).
i. Explain which of the mean values, A–E, is likely to be the least accurate. You should process data from the table to support your
answer.
[2]
ii. Identify one limitation in the practical procedure that may have caused the results to be inaccurate and explain which cube's
results are most likely to have been affected by this limitation.
Limitation
Is more likely to affect cube ….. because
[
(e). The procedure described above involved the use of model cells. Hydrogen ions from the acid were able to travel freely to the centre
of the agar jelly cubes.
The rate of movement of molecules from the plasma membrane towards the centre of living cells is often greater than that seen in the
procedure the student carried out even if the cells are kept at the same temperature.
Suggest a reason for this observation.
[1]
© OCR 2022. You may photocopy
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this page.
