Biological Membranes (OCR AS Biology)

Exam Questions

3 hours35 questions
1a
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2 marks

The fluid mosaic model was first outlined in 1972 and describes the structure of biological membranes.

Name two components of a cell membrane which are entirely or partially made up of proteins.

1b
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2 marks

Other than describing membrane structure, state two other processes that the fluid mosaic model helps to explain.

1c
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3 marks

Describe what the words ‘fluid’ and ‘mosaic’ refer to with regards to membrane structure. 

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2a
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5 marks

Membrane permeability is affected by a number of factors, including temperature, membrane composition and organic solvents.

Increases and decreases in temperature change the permeability of the cell membrane.

(i)

Describe how an increase in temperature changes the permeability of the cell

[1]

(ii)
Explain why the change in (a)(i) occurs. 

[2]

(iii)
Describe the role of cholesterol in reducing the effect of higher temperatures on the membrane permeability. 
[2]
2b
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1 mark

State one component of a cell membrane that would increase its permeability to a specific ion. 

2c
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4 marks

Organic solvents affect the permeability of the cell membrane.

(i)
Name the property of phospholipids responsible for creating a partially permeable membrane structure.

[1]

(ii)
Explain how the cell membrane is affected by organic solvents.

[2]

(iii)
Describe what occurs to membrane permeability as the concentration of organic solvent in a cell’s environment increases.

[1]

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3a
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3 marks

Diffusion is one type of transport which occurs across the cell membrane.

State the definition of diffusion.

3b
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3 marks

Name three factors which affect the rate of diffusion of molecules or ions across the cell membrane.

3c
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3 marks

Using your answer from part (b), describe how each of these factors affects the rate of diffusion.

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4a
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5 marks

Some molecules or ions cannot be transported using passive mechanisms such as diffusion. Active transport must be used.

(i)
State the reason why active transport would be used to move a polar molecule or ion across a cell membrane. 
[1]
(ii)
Name two requirements for active transport.
[2]
(iii)
Describe two processes in living organisms where active transport is important.
[2]
4b
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4 marks

Another kind of active transport is the bulk transport of molecules and ions across the cell membrane. 

(i)

Name two types of bulk transport into cells.

[2]

(ii)
Give two examples of materials that would cross the cell membrane by bulk transport.

[2]

4c
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3 marks

Describe the bulk transport of a protein out of the cell, after it has been processed in the Golgi body.

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5a
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4 marks

Water moves in and out of cells by the process of osmosis.

(i)
Define the term osmosis.
[3]
(ii)

A student adds more solutes to a solution.

Describe the effect this would have on the water potential of the solution.

[1]

5b
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6 marks

Figure 5.1 shows plant cells in different concentrations of solution. 

ocr-a-2-5-e-sq-q5-plant-cells

Figure 5.1

(i)

State what kind of solution Cell 1 and Cell 3 was placed in.

[2]

(ii)

Based on the information in Figure 5.1, describe the osmotic change that has occurred in Cell 1 and Cell 3.

[2]

(iii)
Describe what would happen to an animal cell if it were placed in the same solution as Cell 3.
[2]

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1a
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8 marks

A student investigated the uptake of two different substances in cultured cells.

The rate of uptake was measured at different concentrations of each substance in the medium surrounding the cells.

The results are shown in Fig. 16.2.q16b-paper-1-nov-2020-ocr-a-level-biology

Fig. 16.2
(i)
The student concluded that one substance entered the cells by simple diffusion and the other by active transport.

Evaluate the student’s conclusion.
[4]
(ii)
The student then added 2,4-dinitrophenol (DNP) to the cells. DNP inhibits respiration.

Predict the effect of DNP on the uptake of each substance and explain your prediction.

Substance A
effect ....................................................................................
explanation ........................................................................

Substance B
effect .....................................................................................
explanation .........................................................................
[4]

1b
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4 marks

The student used a colorimeter to measure the concentration of each substance in the liquid surrounding the cells.

The colorimeter had an analogue display. The reading was indicated by a needle moving across a scale. The smallest divisions on the scale corresponded to 0.1 absorbance unit.

After the investigation the student suggested some improvements.

Draw a line between each of the improvements to the corresponding justification.

q16c-paper-1-nov-2020-ocr-a-level-biology

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2a
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5 marks

Water moves by osmosis in living organisms.

(i)
Define osmosis.
[2]
(ii)
Plants rely on osmosis for support.

Explain the importance of osmosis in plant support.
[3]
2b
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4 marks

The apparatus shown in Fig. 16 can be used to demonstrate osmosis.

q16b-paper-2-june-2019-ocr-a-level-biology

Fig. 16

When the capillary tube with visking tubing bag was placed in solution Y, the level of solution X inside the capillary tube rose from 10.5mm to 26.5mm.

(i)
The ruler used to measure the distance along the capillary tube was accurate to the nearest 0.5mm.

Calculate the percentage uncertainty of the measurement.

uncertainty = ............................. % [2]

(ii)
What conclusions can be drawn about the composition of solutions X and Y?

[2]

2c
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7 marks

A group of students used the following method to investigate osmosis in plant cells.

  • Cut pieces of plant material of equal surface area ensuring no skin is present.
  • Rinse to remove cell debris.
  • Gently pat the plant pieces dry with a paper towel.
  • Weigh each piece and record mass.
  • Put the plant piece in a 200cm3 beaker.
  • Cover plant piece with 50cm3 of sucrose solution.
  • Use sucrose solutions of 0, 0.1, 0.3, 0.5, 0.7moldm–3.
  • Leave for 24h.
  • Remove the piece of plant material.
  • Dry carefully using a paper towel.
  • Weigh the plant piece and record the mass.
  • Calculate the percentage change in mass for each piece.
  • Repeat twice for each sucrose concentration.

The students investigated material from three different plants: carrot, courgette and potato.
Their results are shown in Table 16.

Plant Sucrose
concentration /
mol dm-3
Percentage change in mass
Replicate 1 Replicate 2 Replicate 3 Mean

Carrot

0 + 6.0 + 5.8 + 5.8 + 5.87
0.1 + 4.2 + 4.1 + 4.3 + 4.20
0.3 + 1.5 + 1.5 + 1.3 + 1.43
0.5 - 2.4 - 2.3 - 2.1 - 2.27
0.7 - 6.3 - 6.1 - 6.3 - 6.23

Courgette

0 + 7.9 + 7.8 + 7.6 + 7.7
0.1 + 5.5 + 5.5 + 5.5 + 5.50
0.3 + 1.9 + 1.8 + 2.0 + 1.90
0.5 - 1.2 - 1.4 - 1.1 - 1.23
0.7 - 4.3 - 4.4 - 4.1 - 4.27

Potato

0 + 5.7 + 5.8 + 5.7 + 5.77
0.1 + 3.1 + 2.9 + 3.0 + 3.00
0.3 - 0.3 - 0.4 - 6.0 - 0.43
0.5 - 2.4 - 2.2 - 2.5 - 2.37
0.7 - 6.1 - 5.9 - 5.1 - 5.70

Table 16

(i)
Explain why it was necessary to calculate percentage change in mass.
[2]
(ii)
The students identified replicate 3 of the potato in 0.7moldm–3 sucrose as anomalous.

Suggest a practical error by the students that might have caused this result to be anomalous and explain the likely effect of this error.
[2]
(iii)
Use Table 16 to identify which plant cells contained the highest concentration of sucrose.

Justify your conclusion.
[3]
2d
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3 marks

Water has many properties that are essential for living organisms.

Explain how properties relating to the density of water contribute to the survival of organisms.

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3
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4 marks
(i)

Soluble mineral ions are present in soil.

Explain why water molecules can form hydrogen bonds with nitrate (NO3-) ions.

[2]
(ii)
Fig. 18 shows a process that occurs in the cell surface membrane of the endodermis in the root.

q18cii-paper-1-june-2017-ocr-a-level-biology

Fig. 18

Explain how the events shown in Fig. 18 cause water to enter the endodermis.

[2]

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4a
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2 marks

Fig. 1 shows a diagram of part of a cell surface membrane.

4-1-fig-3-1Fig. 1

Identify molecules A and B.

4b
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2 marks

Describe the role of molecule C in Fig.1.

4c
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2 marks

State two functions of molecule D in Fig. 1.

4d
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2 marks

Explain the importance of molecule E in Fig. 1 when the cell is exposed to high temperatures.

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5a
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4 marks

Fig.1 and the key below give information about some molecules found inside and outside a cell.q8c-1-unit-1-june-2021-edexcel-ial-biology
q8c-2-unit-1-june-2021-edexcel-ial-biology

Fig.1

Using the information provided, identify the mechanism by which each of these molecules can enter the cell across the cell membrane. Give an explanation for your choice.

5b
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6 marks

Fig. 2 shows the process which occurs when a phagocyte encounters a pathogen in the blood stream.endocytosis-sq

Fig. 2

(i)

Describe the mechanism by which the pathogen is taken into the cell.

[3]

(ii)

Studies have indicated that high cholesterol levels may lead to a reduced non-specific immune response in patients.

With reference to the process discussed in part (i), suggest an explanation for these findings.
[3]
5c
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3 marks

Leukocyte Adhesion Deficiency (LAD) Syndromes are a group of disorders affecting white blood cells in the body.

One type of LAD that has been identified is caused by a reduction in cell membrane proteins of neutrophils and is characterised by a reduced ability of the body to respond to bacterial infection leading to increased susceptibility to recurrent infection.

Using your knowledge of cell membrane function and the information from this question, suggest how LAD may result in recurrent infections. 

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1a3 marks

Explain the terms ‘fluid’ and ‘mosaic’ in the Fluid Mosaic model of membrane structure.

Give one advantage of the structure being fluid. 

1b4 marks

Give four functions of proteins that occupy the plasma membrane. 

1c3 marks

Pieces of phospholipid bilayer were analysed from two different mammalian cell surface membranes. Sample A contained phospholipid molecules at a density of 5.0 x 106 molecules μm-2, whereas sample B contained phospholipid molecules at a density of 4.1 x 106 molecules μm-2. One sample was from a hormone-secreting liver cell and the other was from a skin cell. 

Identify which cell type corresponds to samples A and B. Give reasons for your choice. 

1d2 marks

Researchers have discovered that an individual phospholipid molecule can exchange places with its neighbouring phospholipid molecule in a monolayer as frequently as 107 times per second. By contrast, phospholipid molecules almost never exchange places with each other from one monolayer to the other within a bilayer, referred to as a ‘flip-flop’ exchange. The ‘flip-flop' takes place around once a month for a typical phospholipid molecule. 

Use your knowledge of membrane structure to explain this difference in molecular behaviour. 

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2a6 marks

Explain how three different factors can affect the fluidity of membranes.

2b5 marks

Identify the structures labelled in Figure 1.1. In each case, state one function of the structure that has been identified.

IOMeeuBe_1Figure 1.1

Structure

Name

Function

A1

   

A2

   

B

   

C

   

D

   

E

   

F

   

G

   

2c4 marks

Outline the main factors that govern the rate of diffusion across a phospholipid bilayer. 

2d4 marks

Distinguish between the features of channel proteins and carrier proteins and their roles in membrane transport. 

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3a6 marks

Design an experiment to estimate the glucose concentration of the cell contents of sweet potato tuber. The following equipment has been provided. 

  • Sweet potato
  • 1 mol dm3 glucose solution
  • Cork borers
  • Other common laboratory supplies and reagents.

Outline the steps you would take and the way that you would process the data that you would generate. 

3b3 marks

Sketch a graph of the expected results from the experiment in part (a). 

3c2 marks

Define the term, ‘water potential’ and explain why values of water potential are expressed in kilopascals (kPa).

3d2 marks

Explain why an aqueous solution has a lower water potential than pure water. 

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4a3 marks

Figure 1.1 shows two configurations of a voltage-gated membrane protein that is found in the cell surface membranes of nerve cells. This protein allows the transport of ions when open. Its role is in the generation and transmission of nerve impulses. 

11_dvm7j_2

Figure 1.1

Suggest the mode of transport of ions that this protein employs, giving reasons for your answer. 

4b2 marks

State and explain one benefit and one drawback of using beetroot tuber as a tissue in studies of factors that affect the permeability of plant cell surface membranes. 

4c2 marks

Explain one advantage to medicine of studying the permeability of the cell surface membranes of bacteria. 

4d2 marks

Active transport via a carrier protein is not the only active mechanism by which substances can cross cell boundaries against their concentration gradients.

Describe and explain one other of such mechanisms. 

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5a4 marks

In a landmark scientific experiment in the 1920s, two Dutch scientists made a new claim about the structure of membranes. They calculated the area of the red blood cell membrane and then extracted the lipids that were present. These were dissolved in petroleum ether and allowed to spread into a tightly-packed layer one molecule thick on a surface of water and the area was measured.

Their data is shown in the table below.

Mean surface area of one red blood cell 

/ μm2

Red blood cell count 

/ cells cm-3 blood

Water surface area covered by lipids extracted per cm3 of blood 

/ cm2

101

4.67 x 109

9,430

 

Explain what the data in the table reveals about the alignment of lipids in the cell surface membranes of red blood cells. Reinforce your explanation with suitable calculations.

5b3 marks

Suggest three refinements of the Dutch scientists' claim that have arisen from subsequent research by other scientists, which have led us towards the currently-accepted model of the structure of membranes. 

5c4 marks

Predict and explain the consequences to digestion if mammalian intestinal epithelial cells were to stop performing active transport of sodium ions. 

5d3 marks

Malabsorption of glucose in the small intestine may lead to diarrhoea.

Explain why. 

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