Defence Against Disease (Edexcel GCSE Biology)

Plants can be infected by a range of pathogens.

Aphids are small insects that feed on plant sugars and carry pathogens.

Figure 1 shows part of a plant infested with aphids.

Figure 1

Plants infested with aphids show signs of reduced growth.

Suggest and explain one reason why.

It is common for plants infested with aphids to show signs of magnesium deficiency.

Describe and explain the symptoms displayed by a plant with a magnesium deficiency.

Plants have methods of protecting themselves from attack.

One such method is the production of oils by cells on the surface of leaves. 

Suggest two ways that the production of oil might protect a plant from being attacked. 

Higher Tier Only

A number of plants in a garden are infected with a pathogen.

Give two ways of identifying the pathogen that is infecting the plants in the garden. 

Explain how different types of organism defend themselves against microorganisms.

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.

Meningitis B and meningitis C are caused by bacteria.

Figure 2 shows the number of cases of meningitis B and meningitis C in England between 1999 and 2004.

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.

Explain how plants protect themselves from being eaten by pests and against diseases caused by pathogens.

Clostridium tetani is a bacterium that can be found in soil.

It causes the infection tetanus.

Children are vaccinated against tetanus.

Explain why these children do not get tetanus if the bacteria enter their body through a cut in the skin.

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

Higher Tier Only

A gardener notices that the leaves of one of his rose plants are falling off and those remaining on the plants are covered in black and purple spots with some areas of decay.

Figure 1

Witch hazel is a plant that produces oil as part of its defence against pathogens.

Many skincare companies extract the oil to use in consumer products. 

The oil prevents bacteria from attacking the plant but is safe to use in skincare products. 

Suggest an explanation for why these oils are safe and effective for use in skincare products.

Scientists working for a skincare company investigated how effective three different plant oils were at preventing the growth of one strain of E. coli bacteria.

Figure 2 shows their results.

Evaluate the effectiveness of the three plant oils.

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.

Suggest an explanation for the pattern shown in the graph in Figure 1.

(2)

(3)

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

(2)

HIV can develop into AIDS (Acquired Immune Deficiency Syndrome). This can happen when the white blood cell count drops below a certain number. CD4 is a protein found on the surface of some types of white blood cells. 

Figure 1 shows how the CD4 count in a blood sample for HIV positive individuals compares to HIV negative individuals.

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.