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A LevelBiologyEdexcel A (SNAB)Exam Questions2. Genes and Health2.1 Gas Exchange, Cell Membranes & Transport

Gas Exchange, Cell Membranes & Transport (Edexcel A (SNAB) A Level Biology)

Exam Questions

42 mins5 questions
1a
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The following micrograph shows mammalian lung tissue.

noqvgfi-alveoli-micrograph

(i)

Identify two properties visible in the diagram that makes this an efficient gas exchange surface.

(2)

(ii)

Explain how the properties identified at part (i) will affect the rate of gas exchange in the lungs.

(2)

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1b
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Pulmonary fibrosis is a chronic lung condition which leads to thickening of the tissue surrounding the alveoli. This affects the diffusion of oxygen into the blood.

Fick's Law of Diffusion can be represented by the following equation:

 rate space of space diffusion space space space straight alpha space space space space fraction numerator surface space area space cross times space concentration space difference over denominator membrane space thickness end fraction

The rate of diffusion in healthy human lung tissue was calculated to be 2.52 x 10-18 molecules µm-2 s-1.

A person suffering from pulmonary fibrosis has alveolar walls that are twice the thickness of those found in healthy lungs.

Which of the following represents the maximum diffusion rate across their alveolar epithelium? 

  ☐ A 1.26 x 10-9
  ☐ B 5.04 x 10-18
  ☐ C 1.26 x 10-18
  ☐ D 2.52 x 10-9

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1c
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Explain the importance of blood vessel A in the diagram at part (a) in gas exchange.

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2a
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The diagram below shows part of a plasma membrane. 

cell-membrane

Complete the table below by writing the letter from the diagram which refers to each part of the membrane.

Part of the membrane Letter
Contains carbon and hydrogen only  
Facilitates communication between cells  

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2b
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Give a function of the structure labelled V in the diagram in part (a).

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2c
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Plasma membranes such as the one seen in the diagram in part (a), are often described as having a fluid-mosaic structure.

Explain why they are described this way.

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2d
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Structures X and Y from the diagram in part (a) form a phospholipid. Collectively, these phospholipids form the phospholipid bilayer of the cell surface membrane.

State three functions of this phospholipid bilayer.

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3a
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A student investigated the effect of different concentrations of sodium chloride on the mass of beetroot tissue. A few large beetroots were peeled and cut into strips. The strips were weighed before being placed in beakers containing sodium chloride solutions of different concentrations (0%, 2%, 4%, 6%, 8% and 10%). Three strips were placed in each covered beaker.

The strips were left in the beakers for 24 hours after which they were removed, blotted dry and weighed again.

The mean percentage change in mass was calculated for each sodium chloride solution.

The following graph shows the results of the investigation.

3a-change-in-beetroot-mass-graph-sq

(i)

Apart from repeating the experiment, explain one improvement that could be made to this investigation.

(2)

(ii)

At which point on the graph was the rate of osmosis the highest? 

(1)

  ☐ A  
  ☐ B  
  ☐ C  
  ☐ D  

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3b
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Deduce a suitable conclusion for this investigation by using the information given at part (a).

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3c
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Pickled beetroot is a popular side dish around the world. Beetroot pieces are added to a brine consisting of white vinegar containing acetic acid. This results in the pickling brine turning a deep red colour.

Explain why this happens.

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3d
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When investigating membrane structure and permeability using beetroot, a colorimeter is used to determine the amount of pigment in different samples.

Which of the following is not correct regarding the use of a colorimeter? 

  ☐ A It provides a quantitative measurement of the concentration of pigment that has leaked from the beetroot cells
  ☐ B The colorimeter must be calibrated before each use to ensure that the correct wavelength of light is used to determine the colour of the solution
  ☐ C It gives a more accurate indication of the colour of the solution in the cuvette by measuring the absorbance of light by the coloured liquid
  ☐ D If a small concentration of pigment is present, then more transmission of light will occur in the cuvette which will be recorded by the colorimeter

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4a
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Some scientists investigated the uptake of magnesium ions in rice plants. They divided the plants into two groups and placed their roots in solutions containing radioactive magnesium ions.

Group Y: plants had a substance that inhibited respiration added to the solution

Group Z: plants did not have the respiratory inhibitor added to the solution

The scientists calculated the total mass of magnesium ions absorbed by the plants every 5 minutes.

Their results are shown in the graph below:

picture4

Calculate the ratio of the mean rate of uptake of magnesium ions in the first 20 minutes to the mean rate of uptake of magnesium ions in the second 20 minutes for group Z plants.

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4b
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Using the graph in part (a), calculate the rate of uptake of magnesium ions for group Y plants after 40 minutes.

Provide suitable units for your answer.

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4c
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Explain the results of the investigation by using the information provided in the graph at part (a).

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4d
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State two differences between the processes of facilitated diffusion and active transport.

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5a
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In the 1930's, Hugh Davson and James Danielli proposed a model of the cell surface membrane.

The diagram below shows this model.

87ATUchp_davsondaniellimembrane

Compare and contrast the Davson-Danielli model of the cell surface membrane with the fluid mosaic model.

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5b
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As technology advanced, scientists could construct a more accurate model of the cell surface membrane which led to the rejection of the Davson-Danielli model.

Describe two such advancements.

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5c
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Structure X in the diagram at part (a) are the components that form the cell surface membrane.

Explain how the properties of X contribute to this.

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5d
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Cholesterol forms an important part of the cell surface membrane.i)

Which of the following correctly describes the role of cholesterol in the cell membrane? 

  ☐ A It prevents the phospholipid tails from packing too closely together when the temperature increases to maintain membrane fluidity
  ☐ B It binds to the hydrophilic tails of phospholipids causing them to pack more closely together when the temperature increases
  ☐ C It prevents the phospholipid tails from packing too closely together when the temperature decreases to maintain membrane fluidity
  ☐ D It binds to the hydrophobic tails of phospholipids causing them to pack more closely together when the temperature decreases

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