3.15 Detecting and identifying plant diseases
5 exam questions worth 12 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 three signs that a plant may have a disease.
Mark scheme
Any three from:
- stunted growth (1)
- spots on leaves (1)
- decay / rot (1)
- growths / galls (1)
- malformed stems / leaves (1)
- discolouration (1)
- presence of pests (1)
Model answer
Stunted growth, spots on the leaves and areas of decay.
A plant has yellow leaves because it lacks magnesium ions.
Explain why this reduces its growth.
Mark scheme
- magnesium is needed to make chlorophyll (1)
- less chlorophyll, so less light absorbed / less photosynthesis (1)
- less glucose for growth (1)
Model answer
Magnesium is needed to make chlorophyll. With less chlorophyll the plant absorbs less light, so it carries out less photosynthesis and makes less glucose for growth.
Explain why a plant lacking nitrate ions has stunted growth.
Mark scheme
- nitrate is needed to make proteins / amino acids (1)
- proteins are needed for growth / making new cells (1)
Model answer
Nitrate is needed to make proteins, and without enough protein the plant cannot make new cells, so it grows less.
Describe two ways a gardener could identify a disease affecting their tomato plants.
Mark scheme
Any two from:
- compare symptoms with a gardening manual / website (1)
- send plant to a laboratory (1)
- use a testing kit (containing monoclonal antibodies) (1)
Model answer
Compare the symptoms with pictures on a gardening website, or use a testing kit containing monoclonal antibodies.
Aphids feed on the phloem sap of plants. Give two ways they can harm the plant.
Mark scheme
- take sugars / sap / food the plant needs (so less growth) (1)
- spread / carry viruses / pathogens (1)
Model answer
They take sugars from the phloem that the plant needs for growth, and they can carry viruses from plant to plant.
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