Microorganisms & Immunity (Edexcel A Level Biology (A) SNAB): Exam Questions

Scientists investigated the presence of bacteria resistant to the antibiotic tetracycline in poultry and in the farmers who kept them.

They looked for Escherichia coli (E. coli) resistant to tetracycline.

The scientists took samples of faeces from the poultry birds and from the farmers. Turkey farmers often used food containing tetracycline, whereas chicken farmers did not. 

The bacteria were grown on nutrient agar containing tetracycline. Resistant bacteria grew and were visible as colonies on the agar plates.

The results are shown in the table below.

Calculate the ratio of the incidence of E. coli found in turkey faeces to that found in chicken faeces.

Describe the results of the scientists’ investigation described in part (a).

Scientists investigated the treatment of a human breathing system infection caused by a species of bacterium. This species of bacterium is often resistant to the antibiotics currently used for treatment. They investigated the use of a new antibiotic to treat the infection. The new antibiotic blocks DNA replication in bacterial cells.

The scientists tested the new antibiotic on mice with the same breathing system infection. The antibiotics were given to the mice at a dose of 25 mg kg⁻¹ per day.

Calculate how much antibiotic would be given to a 33 g mouse each day.

The antibiotic tetracycline is used to treat human bacterial infections such as pneumonia and other breathing system infections. This antibiotic is safe to use in humans as it does not inhibit or block processes such as DNA replication, ribosome function, transcription or translation.

Explain why these processes are not inhibited in humans but can be in bacteria.

In the specific immune system, T cells and B cells share a number of features. One such feature is that they are both lymphocytes that originate in the bone marrow. 

Explain how both types of lymphocytes work together for effective combat of infectious disease. 

A Y-shaped antibody has 2 antigen binding sites, one at each upper tip of the Y shape, as shown below.

(i) Explain how this causes pathogens to agglutinate.

(2)

(ii) Explain the consequences of agglutination to the pathogen.

(2)

The diagram below shows an antibody and its structures. 

Identify the parts labelled B - G and write their names in the table below the diagram. Part A has been completed for you. 

Since the discovery of HIV and the growth of AIDS-related deaths in the 1980s, pharmaceutical companies have managed to reduce the number of AIDS-related deaths through the use of a new drugs regime called Highly Active AntiRetroviral Therapy (HAART).

The graph below shows the progression of AIDS-related deaths in the USA in the period 1981 - 2009, along with the number of cases of individuals who are HIV-positive but are living with the condition. 

Source: National Institute on Drug Abuse

(i) Use the graph to determine the year of introduction of HAART treatment on a large scale in the USA.

Give a reason for your answer. 

(1)

(ii) Calculate the percentage change in the number of deaths in the two year period following your answer to part (a)(i).

State your answer to the nearest whole number. 

(3)

HIV is a known type of retrovirus.

Define the term retrovirus.

An infection with HIV can lead to full-scale symptoms of AIDS.

Despite the infection being viral, many AIDs deaths list the final cause of death as pneumonia, which is a bacterial infection of the breathing system. One common pathogen that causes pneumonia is the bacterium Streptococcus pneumoniae (scanning electron microscope picture below). 

Photo Credit: CDC/Janice CarrContent Providers(s): CDC/Dr. Richard Facklam, Public domain, via Wikimedia Commons

Describe the steps by which HIV can lead to death caused by a bacterium.

Give one reason why a patient who is developing AIDS after an infection with HIV is likely to suffer from infections of increasing severity before developing an infectious disease that has the potential to kill them.

Describe the events that determine whether an antibody molecule will be secreted free-floating in the blood or membrane-bound on the surface of a cell such as a T lymphocyte.

Compare and contrast the primary and secondary immune responses to a given infection.