Defence Against Disease (Edexcel GCSE Biology: Combined Science)

The image in Figure 1 shows the specialised ciliated cells and goblet cells which line the trachea and bronchi of the airways.

Explain how these cells help to protect an individual from harmful pathogens.

Figure 1 shows the antibody concentrations in a mouse after the first and second injections of the same antigens.

Compare the antibody response after the first injection with the antibody response after the second injection.

Describe the role played by phagocytes in the body's defences against pathogens.

Most cases of scarlet fever occur in children.

Adults have usually developed immunity to a toxin that the Streptococcus bacteria produce during infection.

Explain how an adult develops immunity to the toxin.

Describe how the physical barriers and chemical defences of the human body provide protection from diseases.

Chickenpox is a contagious childhood disease. It is caused by the varicella-zoster virus (VZV) and is characterised by the development of an itchy rash as seen in Figure 1.

Children are advised to avoid scratching the area as much as possible to prevent breaking the skin and forming lesions. This is important as lesions in the skin can lead to the development of secondary skin infections.

Chickenpox is a childhood illness which usually individuals would experience just once in a lifetime.

Explain why this is.

There is a vaccination available for protection against chickenpox. It works by triggering a similar response to that discussed in part (b) in order to ensure that the patient would not get ill if they came into contact with the varicella-zoster virus.

Describe two features of the human respiratory system that help to defend the body against diseases, and explain how they carry out their function.

Hypochlorhydria is a condition where the stomach acid is above pH 3.

Suggest why people who suffer from hypochlorhydria may be more likely to develop bacterial infections in the small intestine.

(4)

(4)

Typhoid is a communicable disease caused by the bacterium Salmonella typhi.

(1)

(2)

The graph in Figure 1 shows the number of cases of typhoid and monthly rainfall in Dhaka, Bangladesh. It is estimated that there are around 4 million people living in deprived urban areas in Dhaka.

Figure 1

(2)

(3)

Human Immunodeficiency Virus (HIV) is a virus that attacks and destroys white blood cells.

(2)

A scientist analysed the data in Figure 1 and concluded that “All HIV patients will develop AIDS”.

Suggest two reasons this conclusion may not be correct.

Viruses can undergo genetic mutations which cause proteins on their surface to change.

Explain why a person who has previously been vaccinated against a virus may become infected in the future.