Aim for FiveBiology

Scientific investigation

Selecting for hairier plants

  • Unit 7
  • 4 points
  • About 10 minutes

You can use a calculator on this question, just like on exam day.

A short question about a described lab investigation. You describe a concept behind it, identify part of the method such as a control or a variable to hold constant, state a null hypothesis or predict a result, and justify a prediction. On the exam: Question 3 of 6 in Section II; about 10 minutes suggested.

The question and its sources

Some plants have small hairs called trichomes on their leaves and stems. Students investigated whether the number of trichomes in a population of a fast-growing plant could change through artificial selection.

Investigation

The students grew 150 plants from seed (generation 1) and counted the trichomes along the edge of the first true leaf of each plant. The mean was 22 trichomes. The students then chose the 15 plants with the most trichomes and cross-pollinated them only with each other. They planted the resulting seeds (generation 2) under the same conditions and counted trichomes again.

Source: Hypothetical study

Suggested time: 10 minutes

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Part (a)

1 point

Describe how artificial selection differs from natural selection.

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Part (b)

1 point

Identify an appropriate control group for this investigation.

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Part (c)

1 point

Predict the mean number of trichomes in generation 2 compared with generation 1.

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Part (d)

1 point

Justify your prediction in part (c).

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