AQA A Level Biology

Topic Questions

7.3 Evolution (A Level only)

1a1 mark

Define the term gene pool.

1b2 marks

In a population of snails, there is a range of phenotypic variation.


State two possible factors that are responsible for the variation seen in snails

1c2 marks

The genetic variation in a gene pool is increased as a result of several factors.

Identify one of these factors and explain how it gives rise to genetic variation.

1d2 marks

Some characteristics are polygenic.

Define the term polygenic and give an example of a characteristic which is polygenic.

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2a2 marks

List two different selection pressures that limit the size of a population.

2b1 mark

Define the term differential reproduction.

2c2 marks

Describe the role that differential reproduction plays in altering allele frequencies within a gene pool.

2d2 marks

Suggest why it is not possible for two different species to occupy the same niche.

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3a2 marks

Charles Darwin used the phrase ‘Survival of the fittest’ to support his theory of evolution through natural selection.

State the meaning of this phrase.

3b3 marks

In the 1950’s the myxoma virus spread through wild rabbits in Australia killing 99% of infected rabbits. The virus has since spread to Europe with similar devastating consequences.  However, in recent years, the rabbits have demonstrated a new resistance to the myxoma virus and death rates as a result of infection have dropped.

Explain how natural selection could result in the evolution of rabbits resistant to the myxoma virus.

3c1 mark

State which type of selection is demonstrated by the development of myxoma virus resistance in rabbits.

3d2 marks

Figure 1 shows the reproduction profiles of a rabbit and owl. 

Figure 1

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Suggest how the high reproductive rate of rabbits provides a selective advantage, whilst the low reproductive rate of the owl also provides a selective advantage.

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4a2 marks

Figure 1 shows the average beak sizes of a population of finches of the Galapagos.

Figure 1

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Due to drought, there is a shortage of food causing some finches to utilise different food sources. Individuals in the population with smaller beaks can access smaller seeds and individuals with larger beaks can access larger seeds. Over many generations, the medium sized beaks provided no selective advantage and numbers of finches with medium sized beaks decreased significantly.

Identify the type of selection represented in this example and sketch on the graph how the normal distribution for the average beak size has changed according to the information above.

4b2 marks

Describe the effect that stabilising selection has on a population.

4c2 marks

Table 1 shows some different selection scenarios. For each statement, identify which type of selection has been described. 

Table 1

Statement

Type of Selection

The mean ear length of arctic foxes has decreased over time.

Directional selection

Some species of insect have changed very little over millions of years.

 

Small mammals can hide away from predators, large mammals can resist attack by predators.

 
4d2 marks

In some cases, disruptive selection can result in the formation of two individual species which have evolved from the original population.

Suggest how scientists might confirm whether two individuals from different populations belong to the same species.

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5a3 marks

A population of Cichlids has become separated by geographical isolation into three smaller populations in three separate lakes.

Describe how adaptive radiation results in the evolution of these three populations to form three new species.

5b1 mark

State the meaning of the term genetic drift.

5c1 mark

State the key difference between allopatric and sympatric speciation.

5d2 marks

Sympatric speciation can occur when certain behavioural barriers result in the reproductive isolation of populations.

Suggest one behavioural barrier and explain how it may result in reproductive isolation.

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1a3 marks

Explain how crossing over can contribute to genetic variation.

1b3 marks

In parts of South America, corn seeds are a vital source of food. Seeds can be kept forlong periods of time. Scientists have been able to discover well preserved stores of seeds. Figure 1 shows a graph with three different lengths of seeds collected from different seed stores of different ages.

Figure 1

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Use Figure 1 and your knowledge of genetics and selection to explain the changes in the mean length of seeds between 1650 and 1900.

1c2 marks

Suggest two reasons why corn seeds have increased in length between 1650 to 1900.

1d2 marks

Some of the scientists suggested that the variation of seed lengths represent different species of corn. 

Describe a method that could be used to determine if the scientist's statement is correct. 

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2a2 marks

There are 72 known species of the genus Lygodactylus, many of them found in the continent of Africa and inhabit the same area.

One of these species is the lizard Lygodactylus williamsi is more commonly known as a dwarf gecko. 

Scientists were investigating the number of different Lygodactylus species in one part of East Africa. Describe one way in which scientists could distinguish if the different types of lizards belong to the same species.

2b4 marks

The dwarf gecko lives in the leaf crown of screw pine trees, several metres aboveground, feeding off insects and drinking water from leaves. These trees are located in forest patches in parts of Africa, most especially Tanzania.

Demand for timber for firewood and charcoal production in Tanzania is exceptionally high.

Suggest and explain how speciation may occur as a result of deforestation. 

2c2 marks

Many species of lizards are similar in size and have few differences in their appearance, apart from their colour. 

Suggest how the variety of colour patterns displayed by lizards may help to maintain the lizards as separate species. 

2d3 marks

Dominant male dwarf geckos have a vivid blue colour but females and subordinate males have a copper or green colour. Figure 1 shows a graph that represents the abundance of different colours in a population. 

Figure 1

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Using Figure 1, state and explain the type of variation shown and explain how this type of variation arises.



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3a1 mark

Define what is meant by a gene pool.  

3b5 marks

Rhagoletis pomonella is otherwise known as the apple maggot fly. Initially, these maggots would lay their eggs on hawthorn fruit. In the 19th century a distinct group of maggots emerged that lay their eggs on apples only. Apples and hawthorn fruit are closely related. 

Use this information to suggest how these two species of maggots arose by sympatric speciation. 

3c1 mark

Apple maggot flies tend to exist in smaller population groups. Scientists in North America were studying a group of apple maggot flies in an apple orchard. The farmer was reducing the size of the orchard to make room for grazing cattle. Table 1 shows the size of the apple orchard and the estimated population size. 

 Table 1

Year

Size of Orchard / m2

Population of Apple Maggot Flies / x103

SD +/- 2

1993

347

33

2.3

2001

289

29

1.7

2013

178

15

0.9

2018

81

6

1.1

 

Use Table 1 to calculate the percentage change in the population of apple maggot flies from 1993 to 2018.

3d4 marks

The apple orchard had over 300 trees in 1993, reducing to only 70 in 2018. Scientists estimated the population size by sampling 5 trees from 8 randomly selected areas of the orchard between June and July. They concluded that the reduction in orchard size caused a significant decrease in apple maggot flies between 1993 and 2018. 

Using Table 1 and your own knowledge, evaluate the scientist’s conclusion.

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4a4 marks

The Galapagos Islands are a group of small islands 600 miles off the coast of South America. They are the site of Charles Darwin's famous study of finches. The islands are home to many endemic species of animals and plants which means these species are not found anywhere else. 

Explain how populations can become geographically isolated and how it can lead to speciation

4b3 marks

Another species found on the Galapagos islands are the Galapagos lava lizards. These lizards are found on 12 islets that were likely to have been connected to a larger island called Isla Santa Cruz. 

Explain how the smaller populations of lava lizards on these islets may lead to speciation over time.

4c1 mark

Use the information provided in part b) to state the name given to the type of speciation the lava lizards may experience. 

4d2 marks

The finches on the Galapagos Islands show genetic variation between the islands. One way that variation can arise in populations is by random mutations within genes.

Describe another way in which genetic variation can arise.

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5a1 mark

The levels of lactose intolerance vary across the world. Table 1 shows the different levels of intolerance in two different populations. 

Table 1

Population

Frequency of lactose intolerance in the phenotype

European

0.05

Australian aborigines 

0.97

The lactose digesting gene is dominant and allows people to digest lactose in their diet. 

Using Table 1, calculate the percentage difference in the frequency of heterozygous genotype in the Australian aborigines population compared to the European population.

5b5 marks

The gene coding for the production of lactase, the lactose digesting enzyme, is normally switched off after an infant becomes an adult. Most adult mammals are unable to digest lactose and are lactose intolerant. Many humans have a genetic mutation that prevents the gene coding for lactase from being switched off. This allows these groups of humans to access food sources containing lactose such as milk. 

Mutations preventing lactose intolerance have occurred in humans at various times inthe prehistoric past, and in all human races. The lowest levels of lactose intolerance are found in areas such as Europe and North America. Until recently, Australian aborigines had been isolated in their island continent for almost 50,000 years. 

Using the information provided, suggest how the lactose tolerant phenotype may have arisen in European populations.

5c3 marks

State the type of selection shown in the Australian aborigines population and explain how this takes place. 

5d2 marks

The domestication of large lactating mammals like cattle and goats arose in Europe and parts of Africa between 5,000 to 10,000 years ago. 

Suggest why the frequency of the lactose tolerant phenotype has only recently increased. 

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1a4 marks

The waste material from a zinc mine was left in a grassland habitat. This eventually created a new habitat with high concentrations of zinc in the soil. High levels of zinc are toxic to plants, so no plants were able to grow in this new habitat.

After many years, scientists found a population of daisies growing in this toxic habitat. The daisies belonged to a species (Arctotis acaulis) that normally only grew in the grassland surrounding the mining site. 


Explain how natural selection could produce a zinc-tolerant population of Arctotis acaulis in the mine waste.

1b4 marks

The scientists found that individuals from the population of zinc-tolerant Arctotis acaulis flowered at a different time to individuals from the population of Arctotis acaulis growing in the surrounding grassland habitat, which were not zinc-tolerant.

Explain how this might eventually lead to the production of a new species of daisy.

1c3 marks

Name and define the type of speciation that could occur between the two populations of Arctotis acaulis described in parts (a) and (b).  

1d2 marks

Give two genetic causes of variation between the different members of a population. 

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2a4 marks

The Pyrenean desman (Galemys pyrenaicus) is a small, semi-aquatic, globally threatened mammals related to moles and shrews. It lives in the Pyrenees which is a mountain range between France and Spain. During a study that lasted many years, scientists found that the number of desman travelling from the population on the northern, French side of the mountain range to the population on the southern, Spanish side of the mountain range was extremely low. The scientists suspect that the original desman species may have split into two different species.

If this is true, explain how this may have occurred.

2b2 marks

The scientists found that individual desmans in the northern and southern populations showed phenotypic variation.

State two types of factor that cause phenotypic variation between individuals in a population.

2c3 marks

Name and define the type of speciation that could occur between the northern and southern populations of desmans described in parts (a) and (b).

2d2 marks

State and explain whether genetic drift has a larger impact in smaller populations or in larger populations.

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3a2 marks

A group of biologists conducted an investigation on a remote archipelago (a collection of islands) in the Pacific Ocean. A species of mouse lives on these islands without any natural predators. The biologists measured the claw length of a large number of these mice. 

On half of the islands, a species of snake was introduced that preys on the mice but cannot climb trees. Several years after the snakes were introduced the biologists returned and found that on the island with snakes, the claw length of the mice had changed. Some had shorter claws, enabling them to run faster, while others had longer claws, enabling them to climb trees.

In their investigation of evolution, how could the biologists use the islands that did not contain snakes.

3b2 marks

What kind of selection were the mice in part (a) undergoing? Explain your answer.

3c4 marks

The evolution of long claws in the mice in part (a) was made possible by a mutation in the gene controlling claw length.

i) What is a mutation?

ii) Give a simple definition of evolution.

3d4 marks

When the biologists conducted the investigation in part (a), flooding of the islands was very rare. Now, due to climate change, flooding of the islands occurs more regularly. This flooding can regularly wipe out large numbers of ground-living species.

Using this information and the information from part (a), explain how and why the claw length of the mice on the islands may be changing.

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4a4 marks

Mosquitoes spread a disease called malaria. DDT is a pesticide used to kill mosquitoes. DDT is used in many countries in Africa to try to control the spread of malaria. Some mosquitoes have an allele that gives them resistance to DDT. A group of biologists studied how frequently this allele occurred in a population of mosquitoes in Uganda (in Africa) over 5 years.

The graph in Figure 1 below shows the biologists’ results.

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Explain the results shown by the graph in Figure 1.

4b3 marks

Anaemia occurs when the blood cannot carry enough oxygen. Sickle-cell anaemia is a common condition in people from Uganda and more generally, among people of African descent (as well as among people of Middle Eastern or southern Meditarranean descent). It is caused by a mutation that affects one of the polypeptides in haemoglobin molecules. When the concentration of oxygen is low, affected haemoglobin molecules form fibres within red blood cells, causing them to become sickle-shaped. These sickle cells are targeted for destruction by the immune system and only last about 15 days.


Compared to healthy red blood cells, sickle cells have a shorter life span and smaller surface area. Explain why both these differences result in anaemia.

4c2 marks

Without medical treatment, people with sickle-cell anaemia often die in childhood. Scientists predicted that in countries without reliable access to medical care, the sickle-cell allele should reduce in frequency. Explain why this would be expected.

4d5 marks

Despite the prediction of scientists described in part (c), sickle-cell anaemia remains common in countries without reliable medical care for the condition. Malaria is also prevalent in these countries. The parasite that causes malaria (transmitted between humans by female mosquitoes) enters the human’s red blood cells and uses the oxygen in these red blood cells for their own respiration.

Using all the information provided in parts (b) and (d), suggest why sickle-cell anaemia is common in many countries where malaria is prevalent.

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5a2 marks

The diagram in Figure 1 below shows a phylogenetic tree of mousebirds of the Coliidae family. Mousebirds are distantly related to woodpeckers and kingfishers.

Figure 1

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i)
How many different genera are shown in the phylogenetic tree in Figure 1?

ii)
The phylogenetic tree in Figure 1 is based on the evolutionary history of the What does the information in the diagram suggest about the common ancestors of Urocolius  indicus, Urocolius macrourus and Colius castanotus?
5b2 marks

The white-backed mousebird (Colius colius) lives in southern Africa. Complete Table 1 below to show the classification of the white-backed mousebird.

Table 1

Kingdom

 
 

Chordata

 

Aves

 

Coliiformes

Family

 

Genus

 

Species

 
5c3 marks

In Africa, there are several species of mousebird. They are thought to have arisen by sympatric speciation.

Explain how sympatric speciation may have occurred.

5d2 marks

A group of scientists produced hybrids between two different species of mousebird by fertilising eggs from one species with sperms from another species. Male hybrids had songs that had some features from one of the parent species and some features from the other parent species.

The male hybrids were unable to reproduce. Suggest why.

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