A farmer grows a crop of banana plants. All the banana plants are produced by asexual reproduction. A new fungal disease spreads across the farm. Explain why the spread of this disease could destroy the entire crop of banana plants.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Banana plants can be reproduced asexually by taking cuttings from a parent plant. A fungal disease has recently begun to affect banana crops worldwide.
Model answer (4 marks)
Asexual reproduction produces only one parent plant and its offspring are genetically identical clones.
Because all the banana plants are clones, there is almost no genetic variation in the crop.
If one plant is susceptible to the fungal disease, every other plant has the same alleles and will also be susceptible.
Since no plant in the crop has a resistance allele, the disease can spread through the whole field and destroy the entire crop.
Because all the banana plants are clones, there is almost no genetic variation in the crop.
If one plant is susceptible to the fungal disease, every other plant has the same alleles and will also be susceptible.
Since no plant in the crop has a resistance allele, the disease can spread through the whole field and destroy the entire crop.
Examiner tips
- Use the word ‘clones’ to show you know asexual reproduction gives identical offspring. Show the link between lack of variation and uniform susceptibility. Mention that no resistance alleles exist in the crop. Keep the answer concise – 4 short points will earn full marks.
Common mistakes
- Confusing asexual reproduction with sexual reproduction. Failing to explain that all plants share the same genotype. Omitting the point that no resistance alleles are present.
Mark scheme (4 marks)
- Asexual reproduction involves a single parent / produces genetically identical offspring (clones)
- There is no / very little genetic variation in the crop
- If one plant is susceptible to the disease, all plants are equally susceptible (because they share the same alleles / genotype)
- No individual plants have alleles that give resistance, so the entire crop can be destroyed
Key terms in this question
Related
- All Edexcel GCSE Biology (1BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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