Variation and SelectionCambridge IGCSE Biology: Topic test

20 questions, 54 marks

Cambridge IGCSE Biology

Variation and Selection topic test

Total 54 marks

Name

Class

Date

1
A population geneticist studies a population of ladybirds living in a garden, recording two characteristics: the number of spots on each ladybird's wing cases, which takes only a small number of distinct whole-number values with no intermediates, and the body length of each ladybird, which varies smoothly across a wide range of values.
(a)
Which term describes the variation seen in the number of spots on the ladybirds' wing cases?
[1 mark]
ADiscontinuous variation
BContinuous variation
CAdaptive variation
DEnvironmental variation
(b)
Which term describes the variation seen in the ladybirds' body length?
[1 mark]
ADiscontinuous variation
BContinuous variation
CGenetic variation only
DMutation
(c)
Explain why spot number in ladybirds is usually controlled only by genes, whereas body length is influenced by both genes and the environment.
[2 marks]
Total for question 1: 4 marks
2
A population of wild house mice normally has brown fur. A single mouse is born with unusually pale, almost white fur, as a result of a new change in a gene controlling fur pigment production. This new allele did not exist anywhere in the population before this mouse was born.
(a)
What is a mutation?
[1 mark]
AThe fusion of two gamete nuclei
BThe movement of chromosomes during mitosis
CA random change in the base sequence of DNA
DThe transfer of pollen from an anther to a stigma
(b)
Which of the following is described as increasing the rate at which mutations occur?
[1 mark]
AA balanced diet
BRegular exercise
CAn increase in water potential
DExposure to ionising radiation
(c)
Explain the role that mutation, such as the one that occurred in this mouse, plays in producing genetic variation within a population.
[2 marks]
Total for question 2: 4 marks
3
Emperor penguins live and breed in Antarctica, one of the coldest environments on Earth, where air temperatures can fall below -40 degrees Celsius. An emperor penguin has a thick layer of fatty blubber beneath its skin, a compact, rounded body shape, and closely packed, oily feathers that trap a layer of air next to the skin.
(a)
Describe what is meant by an adaptive feature, and identify two adaptive features of the emperor penguin described above.
[3 marks]
(b)
Explain how each of the two adaptive features you identified helps the emperor penguin to survive in its cold Antarctic environment.
[4 marks]
Total for question 3: 7 marks
4
A pest control company has been using a rodenticide (rat poison) called warfarin to control a population of brown rats living around a large farm. After several years of repeated use, the company notices that the rodenticide is becoming much less effective at killing the rats.
(a)
Explain, in terms of natural selection, how the rat population could have become resistant to the rodenticide over several years of repeated use.
[6 marks]
(b)
Explain the difference between the natural selection process described above and the process of selective breeding that a farmer might use to breed animals with a desired characteristic, and explain the source of the original genetic variation on which both processes depend.
[6 marks]
Total for question 4: 12 marks
5
A sheep farmer wants to breed working dogs that are especially good at herding sheep. Each generation, the farmer selects the dogs that show the strongest natural herding instinct and greatest obedience, and breeds only these dogs together, repeating this process over many generations.
(a)
What is the name of this process, in which humans choose organisms with desirable characteristics and breed them together over many generations?
[1 mark]
ASelective breeding
BNatural selection
CGenetic modification
DMutation
(b)
Which of the following best describes a key difference between selective breeding and natural selection?
[1 mark]
ASelective breeding does not require genetic variation, but natural selection does
BSelective breeding always occurs faster than natural selection because it does not involve reproduction
CSelective breeding is carried out by humans choosing which organisms breed, whereas natural selection results from the environment determining which organisms survive and reproduce
DNatural selection can only occur in plants, whereas selective breeding can only occur in animals
(c)
Explain one disadvantage of using selective breeding to produce working dogs with a very narrow range of desirable characteristics over many generations.
[2 marks]
Total for question 5: 4 marks
6
The deep-sea anglerfish lives in the permanently dark, high-pressure waters of the deep ocean, where food is scarce. It has a modified fin spine that projects above its head, tipped with a light-producing organ containing bioluminescent bacteria, which it uses to lure smaller prey fish close enough to catch.
(a)
The anglerfish's light-producing lure is an example of what type of feature?
[1 mark]
AA discontinuous variation
BA mutation
CA selective breeding outcome
DAn adaptive feature
(b)
Which of the following best explains why the anglerfish's light-producing lure is useful in its deep-sea environment?
[1 mark]
AIt increases the surface area available for gas exchange
BIt allows the anglerfish to attract prey in an environment with no natural light
CIt reduces the anglerfish's need for oxygen
DIt allows the anglerfish to photosynthesise for extra energy
(c)
Explain why an adaptive feature such as the anglerfish's light-producing lure is likely to have become common in the anglerfish population over many generations.
[2 marks]
Total for question 6: 4 marks
7
A restaurant uses a chemical disinfectant to clean kitchen surfaces and kill bacteria. After using the same disinfectant for several years, food safety inspectors find that some of the bacteria surviving on the surfaces are now much harder to kill using the same disinfectant at the same concentration.
(a)
State what is meant by natural selection, using ideas from the scenario above.
[3 marks]
(b)
Explain how, over several years of repeated disinfectant use, the population of kitchen bacteria could have become mostly disinfectant-resistant, and suggest one method the restaurant could use to help reduce the risk of this happening again in future.
[4 marks]
Total for question 7: 7 marks
8
A population of seed-eating finches lives on a small island. Beak depth (thickness) varies continuously among the finches in the population, from birds with shallow, narrow beaks to birds with deep, thick beaks. A severe drought causes most small, soft seeds to become scarce, leaving mainly large, hard seeds as the remaining food supply.
(a)
Explain, using the idea of natural selection, how the drought described above could lead to a change in the average beak depth of the finch population over several generations.
[6 marks]
(b)
Explain why a deep, thick beak can be described as an adaptive feature in this drought environment, and explain why the finch population's continuous variation in beak depth, rather than just two distinct beak types, made this gradual change in average beak depth possible.
[6 marks]
Total for question 8: 12 marks

End of questions