Defence Against Disease (Edexcel GCSE Biology)

Higher Tier Only

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.

Higher Tier Only

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.

Figure 1

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.

Figure 2

(i) Use Figure 2 to calculate the change in the total number of cases of meningitis in 1999 compared with 2004.

(2)

(ii) Immunisation against meningitis C was introduced in 1999.

Describe the effects the immunisation had on the number of cases of both types of meningitis. (2)

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.

(i) Identify the cause of the symptoms and explain the effect it has on the growth of the plant.

(4)

(ii) Figure 1 shows the arrangement of rose plants in the gardener's garden.

Figure 1

The infected plant is labelled I.
The gardener decides to move the plants labelled A and B to the other side of the garden (the area labelled X) to try and prevent the infection from spreading.

He decides not to use a fungicide.

Evaluate the effectiveness of the gardener's decisions in controlling the spread of the infection amongst the plants.  (4)

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.

Figure 2

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.

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.

(i) Explain how lesions in the skin could lead to the development of secondary skin infections in children.

(3)

Cellulitis is an example of a secondary infection of the skin which results in swelling, redness and pain of the tissues in the deeper layers of skin. It can be treated by the use of antibiotics.

(ii) Explain why antibiotics can be used to treat cellulitis caused as a result of chickenpox, but would not be effective in treating the varicella itself.

(2)

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.

(i) Explain how the vaccine would protect an individual from being infected with the varicella-zoster virus.

(3)

(ii) In England, the chickenpox virus is not given as a standard vaccination to children, however, some parents may choose to pay to get their children vaccinated privately.
Evaluate the decision not to give the vaccine as standard to children in England.

(4)

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.

(i) Consuming food contaminated with bacteria can lead to cases of food poisoning. State and explain two things you should do while preparing food to reduce the risk of food poisoning. 

(4)

(ii) The graph in Figure 1 shows the sources of food poisoning cases in the UK from 2010-2014. 

Figure 1

One student concluded that avoiding consuming animal food products would prevent cases of food poisoning. This would include meat, seafood, dairy and eggs.

Using information from the graph in Figure 1, and your own knowledge, evaluate this conclusion.

(4)

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

(i) Bacteria are a type of pathogen.

Name one other type of pathogen.

(1)

(ii) Typhoid is spread through contaminated water and food.

Suggest why typhoid is more prevalent in developing countries.

(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.

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

Figure 1

(2)

(ii) In the UK, typhoid vaccination is offered to people travelling to parts of the world where the condition is common. 

Explain why tourists in Bangladesh who have been vaccinated would not develop typhoid even if they become infected with the typhoid pathogen by drinking contaminated water.

(3)

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

(i) Explain why HIV cannot be treated with antibiotics.

(2)

(ii)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.

Figure 1

Suggest and explain why HIV positive individuals are more prone to develop AIDS and may risk dying from secondary infections. You should include information about the immune response in your answer. Use data from Figure 1 and your own knowledge in your answer. (5)

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.