3.7 Human and plant infections
6 exam questions worth 13 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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Give one example of a plant disease caused by a fungus and one caused by a bacterium.
Mark scheme
- fungus: barley powdery mildew / Erysiphe graminis / rose black spot (1)
- bacterium: Agrobacterium / crown gall (1)
Model answer
Barley powdery mildew is caused by a fungus, and crown gall is caused by the bacterium Agrobacterium.
Describe how tuberculosis spreads and the effect it has on the body.
Mark scheme
- airborne / in droplets from coughs (1)
- damages the lungs (1)
Model answer
TB spreads in droplets when infected people cough, and it damages the lungs.
People with HIV are more likely to develop tuberculosis.
Explain why.
Mark scheme
- HIV attacks / destroys white blood cells / immune cells (1)
- immune system is weakened (1)
- so it cannot destroy TB bacteria / fight the infection (1)
Model answer
HIV destroys white blood cells, which weakens the immune system. The body is less able to destroy TB bacteria, so the infection takes hold more easily.
Girls and boys are offered a vaccine against HPV.
Explain how this reduces the number of cases of cervical cancer.
Mark scheme
- HPV infection can cause / lead to cervical cancer (1)
- vaccine prevents HPV infection (so fewer cancers) (1)
Model answer
Some types of HPV can cause cervical cancer. The vaccine stops people being infected with HPV, so fewer develop the cancer.
Barley powdery mildew covers leaves with a white powder.
Suggest why this reduces the yield of a barley crop.
Mark scheme
- less light reaches the leaf / fewer healthy leaf cells / less chlorophyll (1)
- so less photosynthesis / less glucose for growth / grain (1)
Model answer
The powder stops light reaching the leaf cells, so they carry out less photosynthesis and the plant makes less glucose for growing grain.
Give two ways to reduce the spread of athlete's foot.
Mark scheme
Any two from:
- keep feet clean and dry (1)
- wear flip-flops in changing rooms / showers (1)
- do not share towels (1)
- treat with antifungal cream (1)
Model answer
Keep your feet dry, and do not share towels with other people.
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