Cell Recognition & the Immune System (AQA A Level Biology)

Define the term ‘antigen’.

Once it binds to its specific antigen a T cell divides rapidly and several different types of T cell are produced in large numbers. For example helper T cells (T_H cells) release chemical signals known as cytokines.

State three results of the release of cytokines by helper T cells during the immunological response.

Define the term ‘antibody’.

Contrast antibodies and enzymes.

The common cold, also known simply as a cold, is a viral infectious disease of the upper respiratory tract. Well over 200 virus strains are implicated in causing the common cold, with rhinoviruses being the most common. The graph in Figure 1 shows the proportions of people infected with four different strains of rhinovirus in 2020.

Figure 1

A person may develop the common cold twice within a short time. Use information from the graph in Figure 1 to explain why.

The information in the graph in Figure 1 is valuable to companies who want to develop vaccines for the common cold. Using your knowledge of antigens, explain why.

Rhinoviruses that cause the common cold, such as the strains in Figure 1, may be destroyed by phagocytosis when they enter a human body. Describe how this occurs.

Phagocytosis of a rhinovirus leads to presentation of its antigens. State where the antigens would be presented.

B cells can divide to form plasma cells. Each plasma cell contains many mitochondria and an extensive endoplasmic reticulum. Referring to the function of plasma cells in your answer, explain why these features are important adaptations.

B cells can also divide to form memory cells. In the bloodstream of a person who has recovered from an infection, a collision may occur between a B cell and its complementary antigen, or a collision may occur between a memory cell and the same complementary antigen. State which collision is more likely and explain why.

Helper T cells (TH cells) and B cells both react to antigens. Contrast how these two cell types react to their respective antigens.

Complete the Table 1 below by putting a tick (✔) where the feature is present or demonstrated by the cell type.

Table 1

State four structural differences between human cells and bacterial cells.

When an infection is caused by a bacterium, plasma cells secrete antibodies which destroy this bacterium. However, these antibodies are only effective against a specific bacterium. Explain why this is the case.

Apart from antibodies, give one way in which white blood cells protect the body against pathogens.

There are billions of bacteria living in your large intestine. These vast numbers of harmless bacteria actually help to prevent infection by harmful pathogenic bacteria. Suggest how.

The diagram in Figure 1 shows the structure of an antibody.

Figure 1

Name structures A and B.

How do you know from looking at the diagram in Figure 1 that antibodies have a quaternary structure?

Explain how structure A in Figure 1 ensures that the antibody will only detect one specific antigen.

With reference to antibodies, explain the term agglutination and how it occurs.

Figure 1 below shows an image of a type of phagocyte called a neutrophil. 

Figure 1

multi-lobed nucleus,(A) Lysosomes, and (G) glycogen granules

Use Figure 1 to explain how neutrophils are specially adapted to their role.

When pathogens enter the body, phagocytes carry out a process called phagocytosis. Describe the sequence of events that take place during phagocytosis. 

Explain the events that take place soon after antigen presentation that lead to a specific immune response. 

Chemicals called histamines are also involved in the general immune response, acting by increasing the permeability of the capillary endothelium. Suggest how histamines assist phagocytes in their role.

CAR T cell therapy is a new type of immunotherapy that can be used in the treatment of some cancers. The treatment process is represented in Figure 1 below. 

Figure 1

Describe any differences between a normal patient T cell (stage 1 of Figure 1) and a CAR T cell (stage 3 of Figure 1). Suggest an explanation for your observations.  

Use stages 4-6 in Figure 1 to suggest how CAR T cell therapy aids in the treatment of some cancers.

Suggest two advantages of CAR T cell therapy over more traditional chemotherapy. 

One limitation of CAR T cell therapy is that it is more effective in treating blood cancers than cancers with solid tumours. Use Figure 2 below to suggest why this could be the case.

Figure 1 below shows the appearance of a B lymphocyte before and after it has been activated. 

Figure 1

Explain how the B lymphocyte would be activated.

Use Figure 1 to describe the changes that take place within the B cell when it is activated. Explain the importance of each of these changes to B cell function. 

Rituximab is an antibody used in the treatment of some B cell cancers. Suggest how rituximab might work to destroy cancerous B cells.

When treating more aggressive forms of B cell cancer, rituximab is often combined with more traditional chemotherapies. Figure 2 shows the results of a trial looking at the effects of several different treatments, alone and in combination, on B cells grown in the laboratory.

Figure 2

A medical student concluded that drug combinations are a more effective cancer treatment for human patients than any of the drugs used alone. Use Figure 2 and your own knowledge to evaluate this conclusion. 

Figure 1 below shows the mechanism used by the SARS-CoV-2 virus to infect the cells in the airways of human hosts. 

Figure 1

Use Figure 1 to suggest how SARS-CoV-2 infects human cells.

Figure 2 shows part of the evolutionary tree that contains the SARS-CoV-2 virus.   

SARS-CoV-2 infects human cells while its closest relatives and immediate ancestors infect either bats or pangolins (both species of mammal). Suggest an explanation for how the family of coronaviruses have evolved the ability to infect multiple species.

SARS-CoV-2 causes the disease known as COVID-19. One drug currently being trialled for the treatment of COVID-19 is nafamostat, a drug that is currently licensed for the treatment of other conditions. 

During one trial, scientists investigated the effect of nafamostat on the activity of TMPRSS2 (see Figure 1), and their results are shown in Figure 3 below. 

Figure 3

Use Figure 3 to calculate the Nafamostat concentration at which TMPRSS2 activity is a 75%. Your answer should be in Moles and written out in full (i.e. not in standard form).

Use information from Figure 3 and Figure 1 to suggest how nafamostat might function as a treatment for COVID-19. 

Before the development of DNA sequencing, scientists had to use other methods of determining relatedness between organisms. In 1960 an experiment was carried out on chicks to see whether a skin graft (a technique during which a piece of skin is taken from a donor and transplanted onto the skin surface of a recipient) was an effective way of doing this. A group of scientists used the procedure described below:

- A group of 40 chicks of the same variety of chicken were selected as skin graft recipients. 

- Each chick received four small skin grafts; one from a full sibling, one from a half sibling, one from an unrelated chick of the same variety, and one from a chick of a different variety. 

-The scientists then examined the skin graft each day over the following 20 days and scored it on the condition of the graft. Grafts with a healthy appearance were given a score of 5 and the score decreased with decreasing graft health. 

Explain why the scientists thought that skin grafting and assessment of graft health might be an effective way to determine relatedness between organisms.

Some of the scientists’ results are shown in Figure 1 below. 

Figure 1

Use Figure 1 to state what can be concluded from these results.

Another researcher suggested that the scientists should have included a 5th graft in their experiment.  This graft would have been taken from another place on the recipient chick’s body before being grafted back onto the same recipient. Explain what the purpose of this fifth graft might be.

Suggest and explain three measures that the scientists should have taken, other than that described in part (c), to ensure that their results were valid.