Variation & Evolution (AQA GCSE Biology: Combined Science)

Exam Questions

2 hours14 questions
1a3 marks
a)
Complete Table 1 by putting a tick (✓) in the correct column to say which characteristics in humans are determined by the environment, inheritance or both. 
Table 1
  Caused by the environment Caused by inheritance Caused by both
Skin colour      
Eye colour      
Height      
Blood group      
Scars      
Having attached or detached earlobes      

[3 marks]

1b2 marks
b)
Complete the sentences

Choose words in the box.

Phenotype  Mutations  Replications  Genotype  Evolution 

Within human populations everyone has different characteristics, this is called variation. 

Differences in the DNA causes different characteristics. The DNA in genes changes due to events called _______________ . When this happens it can sometimes, but not always, lead to changes in the _______________ . 

[2 marks]

1c2 marks
c)
Some scientists investigated variation in pea plants growing in a garden. 

They counted the number of peas in each pod, as shown in Figure 1

They did this for all 49 plants in the garden. 

Figure 1

fHgKJ3-i_peas-in-a-pod

Give one environmental factor and one other factor that might affect the number of peas in a pod.

[2 marks]

1d3 marks
d)
Table 1 shows the data that the scientists collected. 

Table 1

Mean number of peas in each pod Number of plants 
5 17
6 14
7 8
8 10

Using the axes in Figure 2, complete the bar chart of the data in Table 1.

You will be awarded marks for:

    • Correctly plotted bars
    • Labelling both axes

Figure 2

peas-in-a-pod-graph-1[3 marks]

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2a1 mark
a)
What is the definition of a population? 

[1 mark]

2b4 marks
b)
A population of beetles exists in an area of forest. 

The beetle's outer shell that protects their wings is called an elytra. These can appear in different colours and patterns. 

The beetles in the forest live mostly in leaf litter that is brown and green in colour. 

They are hunted by predators such as birds. 

Explain how the beetle population changed from having a large diversity of different elytra colours to having mostly brown and green. 

[4 marks]

2c3 marks
c)
The humans that live near the forest build a road through the beetles' habitat. 

The road is too wide for the beetles to cross, causing the two populations to become isolated from each other. 

On one side of the road the leaf litter is cleared and lots of plants with red berries start to grow in the area. 

Suggest how this might cause the two populations of beetles to diverge from one another to the point where they are no longer the same species. 

[3 marks]

2d2 marks
d)

How could the scientists determine whether the beetles were still the same species or not?

[2 marks]

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3a1 mark
a)
Lemons are not a naturally occurring fruit. 

The tree that lemon fruits come from (Citrus limon) originates from a cross between a plant called a bitter orange (Citrus × aurantium) and a citron (Citrus medica).

What is the name of the process that lead to the creation of the Citrus limon?

[1 mark]

3b4 marks
b)
Lemons have a very bitter flavour, some of which comes from the high levels of citric acid in the fruit. 

Describe how the farmers growing lemons will have increased the amount of citric acid over several generations of growing the Citrus limon trees. 

[4 marks]

3c3 marks
c)
Other crop plants have experienced a similar process at the hands of farmers and growers. 

Flavour is one thing that can be improved. 

List three other useful traits that growers look for in their crop plants. 

[3 marks]

3d2 marks
d)
Some people are concerned that this process reduces the amount of genetic variation in the plant populations. 

Why is it important to maintain genetic variation in natural plant populations?

[2 marks]

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4a2 marks
a)
Insulin is a hormone that is used to treat people with a medical condition called Type 1 Diabetes. 

What is the function of insulin in the body?

[2 marks]

4b4 marks

Higher Tier Only

b)
The insulin used by diabetics is produced by genetically modified bacteria. 

Explain the process used to create bacteria that contain the gene for human insulin in their genome. 

[4 marks]

4c2 marks
c)
Before insulin was made in this way, it could only be obtained from sheep and pigs.

Suggest two reasons, other than preventing the exploitation of animals, why it is better to obtain insulin by genetic engineering than from animals.

[2 marks]
4d
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3 marks
d)
After the bacteria have been genetically modified, they are placed in a machine called a fermenter where they can reproduce asexually and increase the number of genetically modified bacteria in the culture. 

The species of bacteria used in this process has a mean division time of 30 minutes.  

If one genetically modified bacteria is added to the culture, how many will there be after four and a half hours? 

[3 marks]

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1a2 marks

(a)

Our species, Homo sapiens, like all species, shows variation.

Explain what is meant by the term ‘variation’.

[2 marks]

1b2 marks

(b)

DNA replication is an essential part of the cell cycle in cells preparing to divide by mitosis.

Sometimes DNA is not replicated correctly.

Suggest how mistakes during DNA replication could impact variation within a species.

[2 marks]

1c
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1 mark

When a cell replicates its DNA during the cell cycle, its DNA replicates itself. Under normal conditions around 150 copying errors are made for each cell division.

There are 3 billion (3 000 000 000 or 3 × 109) base pairs of DNA in every human cell. 

(c)

Calculate the percentage error rate for each human cell division.

State your answer in standard form OR with regular numbers. 

[1 mark]

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24 marks

(a)

Even though nylon wasn't invented until the 1940s, bacteria were soon isolated that could degrade nylon.

The bacterium Paenarthrobacter ureafaciens has special enzymes that allow it to metabolise nylon and use it as a sole energy source.

This is a very simple example of natural selection.

Describe how organisms can evolve through the process of natural selection.

[4 marks]

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3a2 marks

(a)

Humans have been selectively breeding animals and plants for many thousands of years.

For example, dogs can be selectively bred so that they produce fur which does not cause allergies in people.

Suggest two other reasons why dogs might be selectively bred.

[2 marks]

3b4 marks

(b)

Dalmatians are a popular breed of dog but due to extensive inbreeding, they are prone to genetic defects.

All pure-bred Dalmatians produce higher-than-normal levels of uric acid due to a gene mutation.

This can lead to the formation of kidney and bladder stones which have to be surgically removed.

Another breed of dog called Pointer dogs do not possess this faulty gene and have normal levels of uric acid.

Cross-breed Dalmatians, which are about 99% Dalmatian and 1% pointer, look and behave like Dalmatians but crucially do not have the gene mutation which leads to high levels of uric acid. 

Explain how selective breeding was used to produce cross-breed Dalmatians that do not suffer from kidney and bladder stones.

[4 marks]

3c3 marks

(c)

The gene mutation in the pure-breed Dalmatian changes one amino acid in a protein involved in regulating levels of uric acid.

Explain how a change in one amino acid in the protein could stop it from functioning normally.

[3 marks]

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4a3 marks

(a)

A manufacturer wants to develop an extremely strong thread which can be used in their products.

They would like to produce a thread which has the same same properties as spider’s silk, a protein fibre made by spiders which has a high tensile strength.

Explain in basic terms how scientists can use bacteria to produce the spider silk protein.

[3 marks]

4b1 mark

(b)

The hormone thyroxine is produced by the thyroid gland and plays an important role in regulating the body’s metabolism, as well as controlling growth and development.

Hypothyroidism is a medical condition where an individual does not produce enough thyroxine.

The gene for thyroxine can be isolated from a skin cell. Explain why the gene does not have to be taken from cells from the thyroid gland.

[1 mark]

4c3 marks

(c)

Suggest why bacteria are suitable organisms to use in genetic engineering.

[3 marks]

4d3 marks

Higher Tier only

(d)

Explain the role of enzymes and vectors in genetic engineering.

[3 marks]

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52 marks

Selective breeding is particularly useful to farmers who want to produce animals with particular characteristics.

Cow X is a cow in a farmer’s herd that has a higher muscle density than normal when fed the same diet.

The farmer wants to produce more cows like Cow X.

(a)

Suggest why the farmer wants to do this.

[2 marks]

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1a3 marks
a)
Figure 1 shows two species of snakes, the coral snake and scarlet kingsnake. 

Figure 1

mimicry-in-snakes-1

The two snake species share similarities in their appearance with stripes of red, black and yellow, although they are not closely related.

How could scientists determine whether the two snakes were the same species or not?

[3 marks]

1b5 marks
b)

The coral snake is venomous and kills its potential predators.

The scarlet kingsnake is not.

The scarlet kingsnake mimics the colours of the Eastern coral snake. 

Describe how the scarlet kingsnake evolved to mimic the Eastern coral snake. 

[5 marks]

1c6 marks
c)
A group of scientists carried out the following experiment:

They created plasticine models of three species of snake. The snake species were:

    • The Eastern coral snake
    • The scarlet kingsnake
    • The Eastern indigo snake, which is a dark blue non-venomous species of snake native to the same region as the other two in South-Eastern USA.

All three species can experience predation from birds of prey in the area, which attack by swooping down and pecking at the snakes' bodies. 

The scientists placed 20 models of each species in the natural 'native' habitat of all three species together, and the same number of models in a different area where the Eastern coral snakes do not normally live (their 'non-native' habitat) but the birds of prey that hunt snakes do exist.

They left the models for 24 hours and went back and counted the number of bird pecks on the snake models, which they could determine by the imprints in the soft plasticine. The number of pecks represent the number of predation attempts on the snakes. They added up the number of pecks in each of the 20 models for each species and calculated an average number of pecks per snake model. 

The results are shown in Table 1.

Table 1

  Average number of pecks in the Eastern coral snake's native habitat Average number of pecks in the Eastern coral snake's non-native habitat
Eastern coral snake 2 21
Scarlet kingsnake 3 25
Eastern indigo snake 19 18

The scientists concluded:

"Mimicry is large advantage for non-venomous snake species"

Evaluate this conclusion, using evidence from Table 1

[6 marks]

1d3 marks
d)
The same scientists wanted to investigate whether mimicry or camouflage was a more effective strategy for preventing predation in non-venomous snakes. 

Suggest how the scientists could alter the experiment to investigate this question. 

[3 marks]

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2a2 marks
a)
Cepaea nemoralis is a species of snail that shows a large amount of variation in their shell colours and patterns, as shown in Figure 2. 

Figure 2

cepaea-nemoralis-image-1

Explain why it is important that the shells of the snail are so varied.

[2 marks]

2b
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2 marks
b)
Some students wanted to plan an investigation into the effectiveness of each shell colour to camouflage the snails from predators. 

This is the method they used:

    • They collected 40 shells from dead Cepaea nemoralis snails, 20 brown shells and 20 yellow shells
    • They went to three different locations to place the shells: a sand dune, a forest floor, and a grass meadow
    • One student scattered the shells around in a 2m2 area so that both colours were evenly distributed around the area
    • The other student was then given 10 seconds to collect as many of the shells as possible
    • At the end they counted how many of each shell colour the second student had found in the time

They recorded their results in Table 2.

Table 2

Location Number of yellow shells collected after 10 seconds

Number of brown shells collected after 10 seconds

Sand dune 2 12
Forest floor 15 1
Grass meadow 3 9

What is the percentage of yellow shells that were collected in total across all three areas? 

[2 marks]

2c3 marks
c)

What conclusion can be made from the students findings?

Use evidence from Table 2 to support your conclusion. 

[3 marks]

2d2 marks
d)
The conclusion from this study may not be valid. 

Give two reasons why the conclusion you made may not be valid. 

[2 marks]

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3a4 marks
a)
There are a number of wild species of bananas that contain large seeds in the fruits, as shown in Figure 3.

Figure 3

banana-with-seeds-1

The varieties of bananas that we consume do not have large seeds, which improves the experience of eating them.

Banana plants cannot reproduce asexually. 

Seeds play an important role in sexual reproduction in plants and therefore it is not possible for any species to naturally evolve to no longer produce seeds. 

Explain how it is possible for humans to grow varieties of bananas without seeds.

[4 marks]

3b3 marks
b)
There is currently an economically concerning disease called Black Sigtoka that affects banana plants. 

It is a fungal pathogen that causes black streaks to appear on the leaves of the banana plants. 

Explain why this reduces the yield of the banana plants. 

[3 marks]

3c4 marks
c)
One suggested solution to this issue is to breed new banana varieties from wild banana plants that are resistant to the pathogen. 

An alternative solution is to produce genetically engineered banana plants that contain DNA that makes them resistant to the pathogen. 

Compare both solutions to the issue. 

[4 marks]

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4a1 mark
a)

Hepatitis B is a viral infection that can be deadly in some cases. 

There is a vaccine to prevent infection with Hepatitis B that is produced from genetically modified (GM) yeast cells.

The process of producing these GM yeast cells is outlined in Figure 4.

Figure 4

producing-hep-b-vaccine--1

Why was the gene for producing the Hepatitis B antigen selected to be used to produce the vaccine? 

[1 mark]

4b1 mark
b)

Figure 4 shows that the virus DNA and the bacteria plasmid were both cut using the same enzyme, labelled Enzyme 1. 

Enzyme 1 cuts the DNA so that there is a sequence of exposed bases on the DNA strand. These exposed bases are called 'sticky ends' and are free to bind to another DNA strand with the correct complementary bases exposed. 

Figure 5 shows how this works. 

Figure 5

restriction-enzymes-1

There are lots of different types of enzymes that cut DNA, and they all cut the DNA at different base sequences. 

Using Figure 5, suggest why both pieces of DNA in Figure 4 should be cut using the same enzyme.

[1 mark]

 

4c1 mark
c)

The yeast takes the genetically modified DNA in the form of the plasmid and can read the DNA to produce the virus protein. 

Why is it possible for the yeast to be able to produce a virus protein by reading the virus DNA? 

[1 mark]

4d2 marks
d)

Once the yeast has been genetically modified it is placed in a machine called a fermenter. 

What is the purpose of the fermenter in this process?

[2 marks]

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52 marks
a)

Suggest two advantages of trying to preserve endangered species such as the Lady's slipper orchid. 

[2 marks]

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