Exam questions · Biology · Reproduction, Meiosis and Variation
Causes of Variation
- 6 exam questions
- 20 marks
- 9 quick checks
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1 State [2 marks]
State two causes of genetic variation.
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Model answer
Mutation, and sexual reproduction (random mixing of genes in meiosis and random fertilisation).
Mark scheme
- Mutation — 1 mark
- Sexual reproduction — 1 mark
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2 Classify [3 marks]
Classify each of the following as caused by genes, by the environment, or by both: eye colour, a scar, body mass.
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Model answer
Eye colour is caused by genes. A scar is caused by the environment. Body mass is caused by both.
Mark scheme
- Eye colour: genes — 1 mark
- Scar: environment — 1 mark
- Body mass: both — 1 mark
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3 Describe [3 marks]
Describe the difference between continuous variation and discontinuous variation, and give an example of each.
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Model answer
Continuous variation is where a feature can take any value in a range, such as height. Discontinuous variation is where a feature falls into distinct categories with nothing in between, such as blood group.
Mark scheme
- Continuous: any value in a range — 1 mark
- Discontinuous: distinct categories — 1 mark
- A correct example of each — 1 mark
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4 Calculate [2 marks]
The masses of five tomatoes are 82 g, 90 g, 76 g, 88 g and 94 g. Calculate the mean mass.
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Model answer
The total is 430 g, so the mean is 430 ÷ 5 = 86 g.
Mark scheme
- Total of 430 g — 1 mark
- 86 g — 1 mark
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5 Explain [4 marks]
Two plants of the same species have different heights. One is grown in sunlight and the other in shade. Explain whether the difference is genetic or environmental.
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Model answer
The difference is probably environmental, because the plants are of the same species and have been grown in different amounts of light. Light affects the rate of photosynthesis and so the growth of the plant. To be sure, the experiment would need plants that are genetically identical, such as clones, so that any difference must be due to the environment.
Mark scheme
- Probably environmental — 1 mark
- Different amount of light affects growth — 1 mark
- Genes may also differ — 1 mark
- Use clones to test — 1 mark
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6 Explain [6 marks]
A scientist measures the heights of 200 students and the blood groups of the same 200 students. Explain how the data for each should be shown and why they are different types of variation.
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Model answer
Height shows continuous variation, because students can have any height in a range. It is controlled by many genes together with the environment, such as diet. The data should be grouped into classes and shown as a histogram, which will probably be bell-shaped. Blood group shows discontinuous variation, because each student falls into one of a small number of categories such as A, B, AB or O. It is controlled by a single gene, and the environment has no effect. The data should be shown as a bar chart with gaps between the bars.
Mark scheme
- Height is continuous — 1 mark
- Many genes plus environment — 1 mark
- Histogram — 1 mark
- Blood group is discontinuous — 1 mark
- Controlled by a single gene / not by environment — 1 mark
- Bar chart with gaps — 1 mark
Quick check
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1
Which of these is an example of environmental variation?
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C: A scar
A scar is acquired during a person's life and is not caused by genes.
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2
Which of these is caused only by genes?
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A: Blood group
Blood group is controlled by genes, and it is not changed by the environment.
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3
Which is a cause of genetic variation?
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D: Mutation
Mutation creates new alleles, which is a cause of genetic variation.
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4
Which is an example of continuous variation?
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B: Height
Height can take any value in a range, so it is continuous.
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5
Which graph should be used to show blood group data?
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C: A bar chart
Blood group is discontinuous data, so a bar chart with gaps between the bars is used.
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6
Are acquired characteristics inherited?
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B: No
Acquired characteristics do not change the genes in the gametes, so they are not passed on.
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7
Identical twins grow up in different places. One is much heavier than the other. What is the most likely reason?
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A: Environmental variation
Identical twins have the same genes, so the difference must be caused by the environment, such as diet and exercise.
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8
Most human features, such as height, are controlled by...
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D: Many genes
Most characteristics are controlled by many genes acting together.
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9
Why should a sample for investigating variation be large and random?
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C: To avoid bias and give more reliable results
A random sample avoids bias, and a large sample gives a more reliable estimate of the mean and the spread.