Infectious Diseases (CIE A Level Biology)

The diagram in Fig. 1 shows a human immunodeficiency virus (HIV).

Fig. 1

Identify structure B and structure E in Fig. 1.

Structure C plays a very important role in the virus represented by Fig. 1.

Identify structure C in Fig. 1 and state its function in this virus.

HIV infects cells of the immune system called T-helper cells. After HIV has infected a T-helper cell, new HIV viruses are produced.

Outline the process of how new HIV viruses are produced.

When the new HIV viruses are released from the T-helper cell, the T-helper cell lyses (bursts) and is destroyed. This destruction of T-helper cells is very dangerous and could eventually cause the death of someone infected with HIV.

Explain why the destruction of T-helper cells could eventually cause the death of an HIV-positive person.

Tuberculosis (TB) is an example of an infectious disease.

Explain why TB can be considered an infectious disease.

Table 1 below shows the number of TB cases reported during one year in three different countries.

Table 1

Use Table 1 to explain why it is advantageous to provide data on the number of cases per 100 000 population rather than only stating the total number of cases.

Outline why TB has a greater chance of being fatal in people who already have HIV/AIDS compared to people who do not have HIV/AIDS.

Describe the transmission of malaria from an infected person to an uninfected person.

Fig. 1 below is a drawing of an electron micrograph showing a red blood cell of someone infected with malaria.

Fig. 1

From Fig. 1, identify two features that show the malarial parasite is eukaryotic.

The presence of malarial parasites in red blood cells can have various negative effects on the human body.

Outline some of these effects.

Fig. 1 shows the human gas exchange system.

Fig. 1

Name the structures labelled A, B, and C in Fig. 1.

Name a non-infectious disease that affects the human gas exchange system.

Malaria is an infectious disease.

Name the pathogen that causes malaria.

There are a number of vaccines being developed to help control the spread of malaria.

Explain why vaccination programmes have not been able to eradicate malaria.

Fig. 2 shows the distribution of malaria in the Americas in 2012.

Fig. 2

Suggest the factors, other than lack of vaccines, that could be restricting the distribution of malaria to area P.

Viruses share common structural features. Some viruses, such as human immunodeficiency virus (HIV), also have an outer envelope as part of their structure.

Outline the key structural features of viruses.

HIV can remain in a dormant state within infected immune system cells for many years. A person diagnosed as HIV‐positive (HIV+) has the virus but does not have symptoms of HIV/AIDS.

The chances of an HIV+ person developing HIV/AIDS can be greatly reduced with a drug treatment programme known as anti‐retroviral therapy (ART).

In 2010, the World Health Organization (WHO) published recommendations for the treatment of pregnant women living with HIV. This includes both HIV+ women and women who have developed HIV/AIDS.

The publication recommended that all pregnant and breastfeeding women living with HIV should be provided with ART.

Fig. 1 shows the number of pregnant women living with HIV, and the number of these receiving ART, between 2005 and 2013, in low and middle income countries.

From the data in Fig. 1, it can be calculated that 13% of pregnant women living with HIV received ART in 2005.

Calculate the percentage of pregnant women living with HIV that received ART in 2013.

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In a person who has been infected with HIV‐1, the most common strain of HIV, a sample of blood can be tested for the presence of the virus.
One test that can only be used in the early stages of infection involves a monoclonal antibody specific for p24, a structural protein present in the virus.

Fig. 2 is a flow chart outlining the steps in the production of anti‐HIV p24 monoclonal antibody.

Pulmonary tuberculosis (TB) is a contagious bacterial infection that involves the lungs. In the UK, children are vaccinated against this disease.

Discuss the importance of a vaccine in disease prevention and control.

Describe how vaccination can lead to protection against pulmonary tuberculosis.

HIV infects human cells by binding to a cell surface receptor called CD4. This binding causes a shape change in the viral surface glycoproteins, enabling the virus to enter the host cell. A new treatment for HIV involves a monoclonal antibody called Ibalizumab, the action of which is shown in Fig. 1 below.

Fig. 1

Suggest how Ibalizumab works as a treatment for HIV.

A trial looking at the efficacy of Ibalizumab investigated its impact on CD4 cell (also known as helper T cell) count after 25 weeks of treatment.

The results are shown in Fig. 2 for each group of patients.

Fig. 2

State and explain what can be concluded about the efficacy of Ibalizumab from the results shown in Fig. 2.

The bacteria that cause tuberculosis (TB) can be found in many parts of the body including the lungs.

The presence of the pathogen in the lungs attracts phagocytes to the area of infection. The phagocytes release elastase, which digests elastin.

Many people with TB feel tired all the time.

Suggest and explain how the effect of phagocytes on tissues in the lungs leads to people feeling tired all the time.

Discuss the biological factors and social factors that make TB a difficult disease to control.

Malaria is a disease that is caused by a parasite from the genus Plasmodium. The parasite has a complex life cycle that involves humans and the Anopheles mosquito. After transfer from mosquito to human, Plasmodium is transported to the liver where it infects liver cells, after which it leaves the liver cells and infects red blood cells.

Once inside the red blood cells the parasite digests haemoglobin internally into a toxic form known as ferriprotoporphyrin IX (FP). The parasite then converts this FP into a non-toxic molecule called haemozoin. This process is referred to as 'sequestration' and the reaction is catalysed by the enzyme haem polymerase.

Fig. 1 shows the breakdown of haemoglobin inside the malaria parasite.

Fig. 1

One of the symptoms during this stage of a malaria infection is fatigue.

Using the information provided, suggest a reason for this.

Chloroquine is currently one of the most popular forms of treatment for malaria. Chloroquine works by inhibiting the action of haem polymerase.

Suggest how chloroquine may act as a treatment for malaria.

The genetic material of the Plasmodium parasite contains genes involved with the production of several thousand potential antigens on its cell surface. 

Using the information provided, as well as your own knowledge, suggest two possible challenges that scientists face in the development of an effective malaria vaccine.

The Anopheles mosquito serves as a vector for the Plasmodium parasite. Anopheles is prevalent in the tropical and subtropical parts of sub-Saharan Africa. Some scientists believe that global warming may have an effect on the occurrence of malaria.

Predict and explain a possible effect that an increase in global temperatures may have on the occurrence of malaria.