Variation and evolutionOxford AQA IGCSE Biology: Topic test

20 questions, 54 marks

Oxford AQA IGCSE Biology

Variation and evolution topic test

Total 54 marks

Name

Class

Date

1
A science class investigates two characteristics in their year group: the students' heights, which range smoothly from shortest to tallest with no clear separate categories, and their ability to roll their tongue into a U-shape, which every student can either do or cannot do, with no in-between.
(a)
Which term describes the variation seen in the students' tongue-rolling ability?
[1 mark]
ADiscontinuous variation
BContinuous variation
CEnvironmental variation
DAcquired variation
(b)
Which of the two characteristics mentioned shows continuous variation?
[1 mark]
ATongue-rolling ability
BHeight
CBoth height and tongue-rolling equally
DNeither height nor tongue-rolling
(c)
Explain why height shows continuous variation while tongue-rolling ability shows discontinuous variation.
[2 marks]
Total for question 1: 4 marks
2
A population of a fish species living in a lake shows variation in body size. After an increase in the number of large predatory birds hunting at the lake, the average body size of the fish population becomes smaller after several generations, as bigger fish are caught more easily by the birds.
(a)
What is the source of the variation in body size within the fish population, before any selection takes place?
[1 mark]
ADifferences in the fishes' diet only
BThe fish deliberately changing size to avoid predators
CDifferences in the fishes' genes
DRandom deaths unrelated to size
(b)
Why does the average body size of the fish population decrease over several generations after the birds arrive?
[1 mark]
AEvery fish shrinks in size to avoid being eaten
BThe birds only eat fish that have already bred
CFish body size is not affected by genes so cannot change
DSmaller fish are more likely to survive and breed, passing on the genes for smaller size
(c)
Explain how natural selection could explain the fall in average body size of the fish population.
[2 marks]
Total for question 2: 4 marks
3
A biology student is studying two colour forms of a land snail species living in a woodland: pale-shelled snails and dark-shelled snails. The student records the numbers of each colour form found in an area with pale leaf litter compared to an area with dark leaf litter.
(a)
Explain, using the theory of natural selection, why pale-shelled snails would be more common in the area with pale leaf litter, while dark-shelled snails would be more common in the area with dark leaf litter.
[3 marks]
(b)
Shell colour in this snail species is controlled by a single gene with two alleles, giving only pale or dark shells, and no shells of an intermediate colour. Explain why this is an example of discontinuous, rather than continuous, variation, and state one other example of a human characteristic that shows the same type of variation.
[4 marks]
Total for question 3: 7 marks
4
A natural history documentary explains how a population of a small mammal living on an island shows a wide range of body sizes and fur colours, and how, over many generations, natural selection has shaped the population's characteristics in response to the island's environment and predators.
(a)
Explain the difference between genetic variation and environmental variation, and describe, using body size or fur colour as your example, how a characteristic can be affected by a combination of both.
[6 marks]
(b)
Explain, in terms of natural selection, how the island mammal population's characteristics could have changed over many generations to become suited to the island's environment and predators, and why this process takes a long time.
[6 marks]
Total for question 4: 12 marks
5
A farmer keeps records of ear length in a large flock of sheep, finding that ear length varies smoothly across the flock, and separately records which sheep are naturally hornless and which have horns, a characteristic that shows only two distinct forms with no intermediates.
(a)
Which of the two characteristics described shows discontinuous variation?
[1 mark]
AWhether the sheep has horns or not
BEar length
CBoth characteristics equally
DNeither characteristic
(b)
What most likely explains why ear length in the flock shows a smooth range of values rather than a small number of distinct categories?
[1 mark]
AEar length is controlled by a single gene with two alleles
BEar length is controlled by many genes, and may also be affected by environmental factors
CEar length is not inherited at all
DAll sheep in the flock are genetically identical
(c)
Explain why the horned/hornless characteristic shows discontinuous variation.
[2 marks]
Total for question 5: 4 marks
6
A population of a plant species growing in a field shows variation in the length of its roots. Following several unusually dry summers, ecologists find that plants with longer roots have become much more common in the population.
(a)
What is the most likely explanation for the increase in the proportion of long-rooted plants after the dry summers?
[1 mark]
AAll the plants grew longer roots in response to the dry conditions
BRoot length is not controlled by genes, so cannot change between generations
CLong-rooted plants could reach water deeper in the soil, so were more likely to survive and reproduce
DShort-rooted plants changed into long-rooted plants over their lifetime
(b)
Which statement about the plants that survived the dry summers is correct?
[1 mark]
AThey survived by chance, unrelated to root length
BThey were all genetically identical to each other
CThey developed longer roots after birth in response to the drought
DThey were more likely to carry alleles for longer roots, which they passed on to their offspring
(c)
Explain why root length in this plant population is likely to be an example of genetic, rather than purely environmental, variation.
[2 marks]
Total for question 6: 4 marks
7
A conservation charity is monitoring a population of a bird species on a remote island. The birds show a wide range of beak depths, from shallow to deep, and the charity records how the proportion of birds with each beak depth changes following a change in the type of seeds available as food after a drought.
(a)
Explain how natural selection could cause the proportion of deep-beaked birds in the population to increase after the drought changes the type of seeds available.
[3 marks]
(b)
Beak depth in this bird population shows continuous variation. Explain what is meant by continuous variation, and explain why this type of variation, rather than discontinuous variation, allows natural selection to change the population's average beak depth gradually over many generations.
[4 marks]
Total for question 7: 7 marks
8
A wildlife park keeps detailed records of a herd of deer, including both the length of their legs, which ranges smoothly from short to long across the herd, and their antler shape, which falls into one of three clearly distinct types with no intermediate forms. Over several decades, following the introduction of a new predator to the park, the park's records show that the average leg length of the herd has increased.
(a)
Using the deer herd's leg length and antler shape as examples, explain the difference between continuous and discontinuous variation, including what usually causes each type.
[6 marks]
(b)
Explain, using the theory of natural selection, why the average leg length of the deer herd could have increased over several decades since the new predator was introduced.
[6 marks]
Total for question 8: 12 marks

End of questions