Exam questions · Biology · Selective Breeding and Genetic Engineering
GM Crops
- 6 exam questions
- 22 marks
- 9 quick checks
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1 Name [2 marks]
Name the bacterium that is the source of the gene for insect resistance, and name the substance that the gene codes for.
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Model answer
Bacillus thuringiensis. The gene codes for a toxin (a protein) that kills insects.
Mark scheme
- Bacillus thuringiensis — 1 mark
- A toxin / protein — 1 mark
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2 Explain [3 marks]
Explain how a crop containing the Bt gene is protected from insect pests.
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Model answer
The gene from Bacillus thuringiensis is in every cell of the crop plant, so the plant makes the Bt toxin. When a caterpillar eats the leaves, it takes in the toxin, and this kills it, so the crop is not damaged.
Mark scheme
- Plant has the Bt gene — 1 mark
- Plant makes the toxin — 1 mark
- Insects that eat it are killed — 1 mark
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3 Calculate [3 marks]
The yield of a conventional cotton field is 1.8 tonnes per hectare, and the yield of a Bt cotton field is 2.4 tonnes per hectare. Calculate the percentage increase in yield.
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Model answer
The increase is 2.4 − 1.8 = 0.6. The percentage increase is 0.6 ÷ 1.8 × 100 = 33%.
Mark scheme
- Increase of 0.6 — 1 mark
- Divides by 1.8, times 100 — 1 mark
- 33% — 1 mark
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4 Explain [4 marks]
Explain two advantages to a farmer of growing a GM crop that contains the Bt gene.
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Model answer
The crop is protected from insect pests, so less is lost and the yield is higher, and so the farmer makes more money. The farmer also does not need to spray as much insecticide, which saves money and time and reduces the chance of poisoning, and also reduces harm to other insects.
Mark scheme
- Higher yield — 1 mark
- Developed — 1 mark
- Less insecticide — 1 mark
- Developed — 1 mark
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5 Explain [4 marks]
Explain how insects could become resistant to a Bt crop.
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Model answer
Some insects have a mutation that makes them less affected by the toxin. When the crop is grown, only these insects survive and reproduce, and they pass the allele on to their offspring. Over generations, more of the insects are resistant, so the crop no longer protects itself.
Mark scheme
- Mutation gives some resistant insects — 1 mark
- Only resistant insects survive — 1 mark
- They reproduce and pass on the allele — 1 mark
- The proportion of resistant insects increases — 1 mark
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6 Evaluate [6 marks]
Some people are in favour of GM crops and others are against them. Evaluate the advantages and the disadvantages of growing GM crops.
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Model answer
GM crops can have higher yields and need less insecticide, which saves farmers money, reduces pollution and can help to feed a growing population. Crops such as golden rice can also give important nutrients. However, there are concerns. Insect pests may evolve resistance to the toxin, so that the benefit is lost. The toxin or the modified genes might harm other organisms or spread to wild plants, which could reduce biodiversity. The seed is expensive and patented, which may be a problem for poor farmers, and some people worry about the safety of GM food, though no harm has been shown. Overall the benefits seem to be large, but the crops should be tested carefully and used with controls such as refuges.
Mark scheme
- Higher yield — 1 mark
- Less insecticide / less pollution — 1 mark
- Resistance may evolve — 1 mark
- Harm to other species / gene transfer — 1 mark
- Cost / patents / safety concerns — 1 mark
- A reasoned conclusion — 1 mark
Quick check
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1
Which bacterium is used as the source of the Bt gene?
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C: Bacillus thuringiensis
The gene comes from Bacillus thuringiensis.
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2
What does the Bt gene make?
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A: A toxin that kills certain insects
The Bt gene codes for a toxin that kills certain insects.
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3
How does a Bt crop protect itself?
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D: It makes its own insecticide
The plant makes the toxin itself, so insects that eat it are killed.
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4
Which is an advantage of Bt crops?
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B: They need less insecticide
Farmers need to spray less insecticide.
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5
Why might insect pests become resistant to a Bt crop?
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A: Natural selection of insects that survive the toxin
Natural selection favours the insects that survive the toxin.
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6
What is the purpose of a refuge of non-GM crop?
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C: To keep non-resistant insects alive
It keeps some non-resistant insects, which slows down the evolution of resistance.
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7
A farmer sprays a field 5 times, and a Bt field once. What is the percentage reduction in spraying?
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D: 80%
The reduction is 4 out of 5, and \(4 \div 5 \times 100 = 80\%\).
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8
Which is a concern about GM crops?
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B: Genes could spread to wild plants
Genes could spread by pollen to wild plants, or the toxin could harm other insects.
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9
Golden rice was developed to help to prevent which problem?
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A: Vitamin A deficiency
Golden rice makes beta-carotene, which can be converted to vitamin A, and so helps to prevent vitamin A deficiency.