Communicable Diseases, Disease Prevention & the Immune System (OCR AS Biology)

Exam Questions

3 hours38 questions
1a2 marks

Figure 1.1 below shows a series of mature T lymphocytes, each with different specific receptors on their surface membranes.

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Figure 1.1

State why it is important to have T lymphocytes with different specific receptors.

1b2 marks

Describe what happens to a T lymphocyte when it comes into contact with the right pathogen.

1c1 mark

Figure 1.2 shows changes in T cell and pathogen number after an infection begins.

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Figure 1.2

Explain what is happening to the T cell numbers in Figure 1.2 during the early days after the start of an infection.

1d2 marks

Explain the relationship between T cell numbers and pathogen numbers in Figure 1.2 during the early days after infection.

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2a1 mark

Figure 2.1 below shows a representation of a mature B lymphocyte. 

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Figure 2.1


Identify the molecule marked X.

2b2 marks

State the events that need to take place for the mature B lymphocyte in Figure 2.1 to be activated.

Note that the term ‘activated’ here refers to the stimulation needed to initiate cell division by mitosis.

2c2 marks

Figure 2.2 shows part of the B lymphocyte response to infection.


5

Figure 2.2

Describe what is happening at the stage labelled Y in Figure 2.2.

2d2 marks

One of the results of stage Y in Figure 2.2 is the production of antibodies.

State one other result from stage Y.

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3a3 marks

Figure 3.1 below shows a representation of an antibody.

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Figure 3.1

Identify the sections marked A-C in Figure 3.1

3b2 marks

State the role of the section marked A in Figure 3.1 

3c2 marks

Figure 3.2 below shows one way in which antibodies can defend the body against pathogens. 


7

Figure 3.2

Name the process shown in Figure 3.2 and state how it helps to fight infection.

3d2 marks

A patient recovered from an influenza infection, and their blood was found to contain influenza antibodies 6 months later.

Explain why this patient was able to catch influenza again several days after their blood tested positive for flu antibodies.

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4a3 marks

Figure 4.1 below shows the effect of vaccination followed by infection with the same pathogen on antibody concentration in the blood. 

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Figure 4.1

Explain why the vaccine causes an increase in antibody concentration.

4b2 marks

Figure 4.2 shows that when the individual is infected with the same pathogen a few months later, their antibody concentration increases more quickly.

Explain why this is the case.

4c1 mark

For a vaccination programme to eradicate a disease, enough people need to be vaccinated that the disease can no longer spread. State the name given to this level of immunity.

4d2 marks

It can be difficult to reach the level of vaccination described in part c) above because some people are concerned about the use of vaccines.

Give two reasons why people might have concerns around vaccination. 

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5a3 marks

The table below contains information about different types of immunity. 

Type of immunity

Production of antibodies

Presence of memory cells

Example of how it can be gained

Natural, passive

No

 

Across the placenta during pregnancy

Acquired, passive

 

No

An injection of antibodies

Natural, active

Yes

   

Acquired, active

 

Yes

Being vaccinated

Use your knowledge of immunity to fill in the gaps in table above.

5b1 mark

Use the information in the table from part (a) to suggest why babies need to be vaccinated from 8 weeks old.

5c2 marks

When an individual is vaccinated, they can remain susceptible to a disease for a few weeks afterwards.

State why this is the case. 

5d2 marks

Tetanus is a bacterial infection gained from contact between the blood and soil-dwelling bacteria Clostridium tetani. An individual who had not been vaccinated against tetanus received a cut from a garden fork and it was suggested that they should go to the hospital for an injection of tetanus antibodies.

State how this injection would protect them against tetanus.

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6a3 marks

Figure 6.1 below shows a representation of the Human Immunodeficiency Virus (HIV).

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Figure 6.1

Identify the structures labelled A-C on Figure 6.1. 

6b2 marks

Name the enzyme labelled enzyme X in Figure 6.1 and state its role.

6c2 marks

Figure 6.2 shows three stages of the process during which HIV infects Helper T cells.

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Figure 6.2

Describe the events that take place in order for step 2 in Figure 6.2 to progress on to step 3.

6d2 marks

State how the events shown in Figure 6.2 lead to the development of AIDS. 

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7a
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4 marks

Describe the process of antibiotic resistance in bacteria. Use the following terms as part of your answer:

  • Variation
  • Mutation
  • Competition
  • Genes

7b
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4 marks

Complete the table below to show the consequences of antibiotic resistance. 

Possible consequence of antibiotic resistance True ✓ or False X
Antibiotics become more effective  
Development of 'superbugs' such as MRSA  
Bacteria contain many resistance genes  
Antibiotic resistance gene passed between species  

7c
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2 marks

The gene(s) for antibiotic resistance can be passed on via vertical or horizontal transmission.

Match up the terms with their correct description.

Horizontal transmission   Resistance gene in plasmid is transferred to a non-resistant bacterium via conjugation
Vertical transmission  

Resistance gene in plasmid is transferred asexually via binary fission

7d
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3 marks

State three ways antibiotic resistance can be reduced.

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1a
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5 marks

The human body is able to protect itself from disease in a variety of ways.

The table shows a list of cells and structures.

Letter Cell or structure
A antigen-presenting cells
B erythrocytes
C goblet cells
D lymphocytes
E lysosomes
F mucous membranes
G neutrophils
H phagosomes
I platelets
J skin

(i)

Which letter or letters indicate cells or structures involved in preventing the entry of pathogens into the body?

 [1]

(ii)

Which letter or letters indicate cells or structures that act as a physical barrier to the entry of pathogens?

 [1]

(iii)

Which letter or letters indicate cells or structures that are involved in phagocytosis?

 [1]

(iv)

Which letter or letters indicate a tissue?

Explain your answer.

 [2]

1b
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2 marks

Phagocytosis involves cytokines and opsonins.

State the role of cytokines and opsonins in phagocytosis.

1c
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3 marks

Chickenpox is a common disease.

People who have recently recovered from chickenpox can donate plasma so that their antibodies can be given to leukaemia patients with weakened immune systems.

(i)
Use a tick (✓) to indicate in the table below which type of immunity is functioning in a leukaemia patient when given chickenpox antibodies.

Type of immunity  
natural and active  
natural and passive  
artificial and active  
artificial and passive  

[1]

(ii)

Explain your answer to part (i)

[2]

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2a
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2 marks

An individual’s immune responses can change throughout their lifetime.

Fig. 4.1 shows one person’s immune response to the influenza virus when they were first infected and when they were infected two years later by a new, mutated strain of the virus.

The influenza virus has many antigens to which the immune system can respond. Fig. 4.1 shows the response to four of these antigens (A–D).q4a-paper-3-june-2019-ocr-a-level-biology

Fig. 4.1

Explain the differences in the person’s initial immune response to the influenza virus with their immune response two years later.

2b
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6 marks

The specific immune response involves B and T lymphocytes.

There is variation in specific immune responses between individual animals.

Variation between immune responses can be influenced by genes and the environment.

Using examples, explain how both genes and environment can cause animals to vary in their specific immune responses.

2c
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2 marks

It is possible to manufacture antibodies to treat certain diseases. These are known as synthetic antibodies.

DNL-Fab3, shown in Fig. 4.2, is an example of a synthetic antibody.q4c-paper-3-june-2019-ocr-a-level-biology

Fig. 4.2

State two conclusions that can be drawn from Fig. 4.2 about the differences between the way DNL-Fab3 functions and the functioning of normal antibodies.

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3
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2 marks

Some microorganisms can be used by humans in industry. Some microorganisms are pathogenic.

Pathogenic microorganisms are transmitted in various ways.

Complete the following passage about the transmission of pathogenic microorganisms using the most appropriate terms.

Some pathogens are carried between host organisms by animals, which are often insects.

These animals suffer no symptoms of the disease and are known as ..................................... .

Other pathogens, such as P. infestans that causes potato blight, produce reproductive structures called ...................................., which can be carried on air currents to infect other hosts.

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4a
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2 marks

All organisms exchange gases with their environment.

Organisms can use simple diffusion to exchange gases when the diffusion pathway is less than 1mm.

A beet armyworm larva:
   •     has a cylindrical shape
   •     is 15mm long
   •     has a volume of 30mm3.

Calculate the diffusion pathway of the larva and state whether it could or could not rely on simple diffusion across its external surface to meet its gas exchange requirements.

Use the formula: Volume of a cylinder = πr2l

diffusion pathway = ........................................................ mm

larva ........................... rely on simple diffusion

4b
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4 marks

Beet armyworm larvae eat a variety of plants, including tomato plants.

Scientists wanted to investigate how effective a chemical called methyl jasmonate was in stopping beet armyworm larvae from eating plants. They sprayed tomato plants with different concentrations of methyl jasmonate and recorded the final biomass of the plants.

The results are shown in Fig. 5.1.q5b-paper-3-june-2019-ocr-a-level-biology

Fig. 5.1

The scientists wrote the following hypothesis:

Plants use methyl jasmonate as a defence against herbivory.

(i)

What additional information do the scientists need to confirm their hypothesis?

[2]

(ii)

Suggest one valid conclusion it is possible for the scientists to draw from the results in Fig. 5.1.

 [1]

(iii)

The scientists also recorded the level of cannibalism amongst the beet armyworm larvae.

Cannibalism was measured as the number of beet armyworm larvae eaten by other beet armyworm larvae.

The results are shown in Fig. 5.2.

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Fig. 5.2

Suggest one valid conclusion it is possible for the scientists to draw from their results shown in Fig. 5.2.

 [1]

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5a
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2 marks

The potato plant, Solanum tuberosum, is a staple food plant in many parts of the world.

Potatoes are susceptible to infection by a pathogen called Phytophthora infestans, which causes a disease known as potato late blight. The most visible sign of the disease is a brown discolouration of the leaves.

Some varieties of potato are resistant to infection by P. infestans.

State two ways in which an individual S. tuberosum plant could respond to infection by P. infestans.

5b
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12 marks

The resistance of different varieties of S. tuberosum to infection by P. infestans was investigated.

  • Three different clones, A, B and C, of S. tuberosum were used.
  • The clones were grown in adjacent fields over the same time period.
  • The percentage of leaf area affected by the disease was estimated at regular intervals.

The results are shown in Fig. 18.q18b-paper-2-june-2017-ocr-a-level-biology

Fig. 18

(i)

Suggest why it is important to use clones in an investigation such as this.

 [2]

(ii)

State how a clone of potatoes could be produced for this investigation and explain why it is important to carry out this procedure under aseptic conditions.

 [2]

(iii)

The extent of infection is estimated by comparing the area under the curve from the graph. The area under the curve for clone B is 1250. (Units can be ignored in this instance.)

 

Using Fig. 18, calculate the approximate area under the curve, between day 35 and day 98, for clone C.

[3]

(iv)

Calculate the area under the curve for clone C as a proportion of the area under the curve for clone B.

 [1]

(v)

Using Fig. 18, suggest why the area under the curve is used as a measure of infection rather than the area of leaf that is visibly affected on a given day.

 [2]

(vi)

The clones were planted in adjacent fields in order to control variables such as temperature, wind speed and rainfall.

Suggest two other abiotic variables that this precaution was intended to control.

[2]

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6
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5 marks

Plague is caused by the bacterium, Yersinia pestis.

(i)

The bacterium is a rod-shaped cell that is approximately 3 μm long.

Yersinia pestis is viewed using a light microscope with a magnification of 1250.

What would be the length of the cell in the image produced by this microscope?

Give your answer in mm.

[2]

(ii)

Photographs taken of the image obtained by the light microscope could be further enlarged using a projector.

Why might the enlarged image be unable to tell us more about the structure of Yersinia pestis?

[1]

(iii)

Outbreaks of plague still occur occasionally. Plague is transmitted by several methods including droplet infection, close contact between people and fleas moving between infected rats and people.

Suggest two ways to minimise the spread of an outbreak of plague.

[2]

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7a
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2 marks

Botulism is a condition resulting from the action of botulinum toxin. The main symptom of botulism is skeletal muscle weakness, which can be fatal.

(i)

Botulinum toxin is produced by the anaerobic bacterium Clostridium botulinum. What information does the word ‘anaerobic’ suggest about the bacterium?

[1]

(ii)

The toxin is initially produced as a large single polypeptide that has low potency.

After the toxin has been acted upon by a protease, two chains are produced which remain connected by a disulfide bond. In this form it is far more toxic.

Describe the action of the protease when it acts on the toxin.

[1]

7b
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5 marks

A mouse assay, using 99 mice, was used to determine the median lethal dose of the toxin.

(i)

Suggest what is meant by the term median lethal dose.

[1]

(ii)

The median lethal dose of the toxin is in the range of 5 – 50 ng kg-1 body mass, depending on the toxin type and the method of introduction into the body.

Calculate the probable lethal dose of the least toxic botulinum toxin for an individual with a body mass of 85 kg.

Give your answer in μg.

[2]

(iii)

The toxin acts primarily at the cholinergic nerve terminals of stimulatory motor neurones. Part of the molecule binds irreversibly to specific receptors on the presynaptic membrane. The toxin–receptor complex is then taken into the cytoplasm of the neurone where the disulfide bond is broken, releasing the section of the molecule which acts to block the release of the neurotransmitter.

Explain why botulism can be fatal.

[2]

7c
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6 marks

There are a number of different strains of the Clostridium botulinum bacterium. Different strains produce immunologically distinct forms of the toxin.

Explain why the toxins produced by the different strains are described as being ‘immunologically distinct’ and how they will be dealt with by the immune system.

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8a
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1 mark

There will be outbreaks of new infectious diseases in the future. They will arise from mutations in the genomes of existing organisms. The mutating organisms may not at present be pathogenic, or they may be animal pathogens that mutate to become able to infect humans.

What feature of a pathogen such as Mycobacterium tuberculosis could be altered by a mutation, making a vaccine ineffective?

8b
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5 marks
(i)

Outline the processes that lead to the production of antibodies against an unfamiliar bacterium.

[3]

(ii)

Explain how helper T cells act to speed up these processes.

[2]

8c
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4 marks

Fig. 16.1 shows the concentration of new antibodies in the blood of a person infected for the first time by a pathogen, on day 0. This is their ‘primary response’.
q16c-paper-2-specimen-ocr-a-level-biologyFig. 16.1

(i)

On day 30, this individual was again infected with the same pathogen. Sketch a line on Fig. 16.1 to show the antibody concentration from day 30 onwards.

[2]

(ii)

Explain how memory cells caused the differences between the two lines on the graph.

[2]

8d
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6 marks
(i)

It takes time for an effective vaccine to be prepared in quantity for a new strain of bacterium.

List two vulnerable groups of people for whom you would advise doctors to prescribe antibiotics although they are not yet showing symptoms of the new disease.

[2]

(ii)

Discuss the implications of the over-use of antibiotics when people do not show symptoms.

[4]

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