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2 D Movement of Molecules
Time: 27 minutes
Total marks available: 27
Total marks achieved: ______
Andy Todd
Q1.
(a) The diagram shows a plant cell drawn by a student.
(i) Label the diagram to show the selectively permeable membrane.
(1)
(ii) Name three parts of a typical plant cell that are not found in an animal cell.
(3)
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(b) The diagram shows a glass container divided in half by a selectively permeable membrane.
One half contains water and the other half contains sucrose solution.
(i) Complete the diagram below to show the change to the level of the water
and the level of the sucrose solution after one hour.
(1)
(ii) Name the process that causes the change in the level of the water and the level of the
sucrose solution.
(1)
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(Total for question = 6 marks)
Q2.
John wanted to investigate the effect of the size of potato tissue on the rate of osmosis.
He cut three different sized cubes of potato, one 0.5 × 0.5 × 0.5 cm, one 1 × 1 × 1 cm
and one 2 × 2 × 2 cm.
He weighed the potato cubes and recorded their masses.
He then placed each cube into a beaker of distilled water and left them for 1 hour.
He weighed them again and recorded their new masses.
In each case the mass of the potato cubes increased.
The table shows his results.
His teacher told him to calculate the percentage change in mass of each cube.
(a) (i) Calculate the percentage change in mass for the 1 × 1 × 1 cm cube.
Show your working.
(2)
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(ii) Explain why John converted change in mass to percentage change in mass.
(1)
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(b) Use your knowledge of osmosis to explain why the mass of each cube increased.
(3)
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(c) John's teacher suggested that the different sized cubes have a different surface area
and volume.
Use the formulae below to calculate the surface area (SA) of each cube, the volume (Vol)
of each cube and their SA:Vol ratios.
SA = 6 × (cube side in cm)2
Vol = (cube side in cm)3
Write your answers in the table below. One cube has been done for you.
(3)
(d) Explain the effect of the different SA:Vol ratios on the rate of osmosis into the potato.
(2)
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(e) Potato tissue is made from plant cells.
Draw and label a plant cell in the space below.
(3)
(Total for question = 14 marks)
Q3.
The diagram shows the nitrogen cycle. Different stages have been numbered 1 to 8.
(a) The table lists the stages involved in the nitrogen cycle.
Complete the table by giving the correct number, or numbers, corresponding to
each stage.
The first one has been done for you.
(4)
(b) Explain how nitrates are absorbed into plants at stage 8.
(3)
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(Total for question = 7 marks)
Q1.
Part (a) examined basic knowledge of plant and animal cells. Most students were able to label
the cell membrane and to name the cell wall, vacuole and chloroplasts as the parts of a typical
plant cell not found in an animal cell. In part (b), it was pleasing to note that many students were
aware that osmosis was responsible for the change in the level of water and duly completed the
diagram to show a lower water level on the left hand side of the container compared to the right
hand side of the container.
Q2.
The question gave data from a variation on a familiar experiment on osmosis in
potato. In (a)(i), most were able to calculate the percentage change in mass but
in only the best candidates were able to explain that calculating the percentage
change enables us to compare different starting masses in (ii). This is a common
practice in many experiments and the examiners were disappointed that many
candidates did not understand its purpose. However, in (c), almost all were able to
explain why the potato cubes gained mass. Most could also calculate the surface
area, volume and surface area to volume ratio of the cubes when given the
formula. In (d), many could describe the relationship between cube surface area
to volume ratio and rate of osmosis. In (e), candidates had to draw and label a
plant cell, with most gaining full marks although a few confused cell wall and cell
membrane.
Q3.
This question gave a diagram about the nitrogen cycle and in part (a) students had to identify the
correct stages. Many scored 3 or 4 marks out of 4. In part (b) students had to explain how
nitrates are absorbed into plants. The best responses described how ions are absorbed into the
root hair cells by active transport against a concentration gradient using energy from respiration.
Q1.
Q2.
Q3.