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A-Level Biology May/June 2025 Q3(c)(i): One of the changes that occurred during the domestication of wild rice to cultivated ri…
A-Level Biology · Paper 9700/42 · May/June 2025 · Question 3(c)(i) · [4 marks]
One of the changes that occurred during the domestication of wild rice to cultivated rice was the loss of the awns from rice grains. Farmers found that long awns made storing and processing rice grains more difficult. It was also observed that rice plants that have grains with no awns have an increased grain yield. Explain the principles used by farmers to produce rice plant grains with no awns.
A full-marks model answer with a mark-by-mark examiner breakdown is below.
1 answer
- accepted ✓
This process is known as artificial selection, where humans act as the selection pressure.
- Farmers would identify and select individual rice plants that naturally show the desired characteristic of having no awns on their grains.
- These selected plants are then interbred with each other, or allowed to self-pollinate, to produce the next generation.
- The seeds from this cross are collected and grown into offspring.
- This process of selection and breeding is repeated over many successive generations. Over time, this leads to an increase in the frequency of the allele(s) for the 'no awns' trait within the cultivated rice population, and the characteristic becomes common.
How the marks are awarded
- MP1 — The model answer correctly identifies the process as 'artificial selection' or states that 'humans act as the selection pressure'.
- MP2 — The answer specifies the selection step: choosing rice plants with the desired trait of 'no awns'.
- MP3 — The answer describes the breeding step, stating that the selected plants are 'interbred with each other' or pollinated.
- MP5 — The answer correctly states that the entire cycle of selection and breeding must be 'repeated over many successive generations' to establish the trait.
Common mistakes
- Confusing artificial selection with natural selection, for example by mentioning environmental pressures or 'survival of the fittest' instead of human choice.
- Being too vague, e.g., saying 'farmers select the best plants' without specifying the desirable trait mentioned in the question ('no awns').
- Describing only a single generation of selection and breeding, and failing to mention that the process must be repeated over many generations to be effective.
- Incorrectly describing genetic engineering (e.g., gene transfer) instead of the traditional breeding methods implied by the context of domestication.
Examiner tip: For application questions, always name the core biological process first, then systematically describe each step of that process using the specific details provided in the question.
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