Explain why tobacco mosaic virus (TMV) reduces the growth of infected plants.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Tobacco mosaic virus (TMV) is a widespread plant pathogen that infects many species, including tomatoes and peppers. Plants infected with TMV show a distinctive mosaic pattern of discolouration on their leaves.
Model answer (4 marks)
TMV infects chloroplasts, damaging chlorophyll and causing the leaf mosaic pattern.
The damaged leaf areas cannot photosynthesise at the normal rate.
As a result, less glucose is produced.
With less glucose available, the plant has less energy and fewer raw materials for cell division, protein synthesis and cellulose production, so growth is reduced.
The damaged leaf areas cannot photosynthesise at the normal rate.
As a result, less glucose is produced.
With less glucose available, the plant has less energy and fewer raw materials for cell division, protein synthesis and cellulose production, so growth is reduced.
Examiner tips
- Use the word ‘cause’ to link TMV infection to chloroplast damage. Show the chain: TMV → chlorophyll loss → reduced photosynthesis → less glucose → reduced growth. Mention energy and raw materials explicitly.
Common mistakes
- Failing to mention chlorophyll damage or photosynthesis. Using vague terms like ‘less energy’ without linking to glucose. Omitting the final link to cell division and growth.
Mark scheme (4 marks)
- TMV causes a mosaic (discolouration/pattern) on leaves, meaning chloroplasts are damaged or the leaf is unable to produce normal chlorophyll
- Discoloured/affected areas of the leaf cannot photosynthesise (at the normal rate)
- Less glucose is produced by photosynthesis
- Less glucose means less energy / fewer raw materials available for growth (cell division / protein synthesis / cellulose production)
Key terms in this question
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