AQA GCSE Biology: Combined Science

Topic Questions

6.1 Reproduction

1a5 marks
a)
Mitosis and meiosis are two types of cell division. 

Complete Table 1 by identifying whether the statements in the table are describing mitosis or meiosis.

The first one has been done for you. 

[5 marks]

Table 1

  Mitosis or meiosis?
How gametes are made Meiosis
Produces four daughter cells  
How fertilised egg cells divide  
Daughter cells contain half the number of chromosomes as the parent cell  
Occurs during asexual reproduction  
Required for growth  
1b1 mark
b)
In humans, the gametes are the egg and sperm cells. 

How many chromosomes are contained in each gamete?

[1 mark]

  • 46

  • 48

  • 24

  • 23

1c2 marks
c)

Identical twins come from one fertilised egg splitting into two embryos. This means that they have the same DNA as each other. 

Although they are genetically identical, identical twins don't often look the same as each other. 

Why is this the case?

[2 marks]

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21 mark
a)

In 1953, scientists Watson and Crick published their work on the structure of DNA. 

What term is used to describe the shape of DNA? 

[1 mark]

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3a1 mark
a)

Haemochromatosis is an inherited condition where iron levels in the blood slowly build up and can cause damage to organs if left untreated. It is caused by a recessive allele. 

What is the definition of the word allele?

[1 mark]

3b3 marks
b)
Two parents without haemochromatosis decide to have children.

Complete the genetic diagram in Figure 2.

    • Identify any children with haemochromatosis.
    • Give the probability of any children having haemochromatosis.

The following symbols have been used:

H = dominant allele for not having haemochromatosis

h = recessive allele for having haemochromatosis

[3 marks]

Figure 2

punnett-square-3

3c1 mark
c)
What is the genotype of each of the parents?

Pick one option:

    • Homozygous dominant
    • Heterozygous
    • Homozygous recessive

[1 mark]

3d
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2 marks
d)
Using your answer to part b, calculate the probability that the couple's next child will be a girl with haemochromatosis. 

Use the equation:

Probability of a girl with haemochromatosis = probability of haemochromatosis x probability of being a girl

[2 marks]

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4a1 mark
a)
The genetic disorder Down's syndrome is a condition caused by a change in the chromosomes.

Figure 3 shows the chromosomes from one cell of a person with Down's syndrome.

Figure 3

down-syndrome-karyotype-1

How does Figure 3 show that this person is female?

[1 mark]

4b2 marks
b)
Describe how the chromosomes shown in Figure 3 are different from the chromosomes from a person who does not have Down's syndrome. 

[2 marks]

4c1 mark
c)
As a woman gets older, the chance of her having a baby with Down's syndrome increases.

Figure 4 shows this.

Figure 4

genetic-disorder-graph-1

The chance of a 25-year-old woman having a baby with Down's syndrome is 1 per 1000 births.

What is the chance of a 40-year-old woman having a baby with Down's syndrome?

[1 mark]

4d3 marks
d)

Some older mothers may choose to undergo embryo screening.

(i) What is embryo screening?

[1 mark]

(ii) Why do some people disagree with the practice of embryo screening for pregnant women?

[2 marks]

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1a2 marks
a)
Figure 1 shows the life cycle of a fungus. 

n represents the number of chromosomes. 

Figure 1

fungi-life-cyle-1

Using Figure 1, name process A and process B. 

[2 marks]

1b2 marks
b)
Compare the genetic composition of the spores that are produced after process A and process B to each other, and also to the parent cells. 
[2 marks]

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2a3 marks
a)
The Human Genome Project was a scientific endeavour to work out the sequence of base pairs in the entire human genome. 

The project was a collaborative effort involving scientists from all over the world. 

It ran from 1990 to 2003 and cost around $2.7 billion.

More than three billion base pairs were identified during the project. 

Explain why it is important for humans to understand the human genome. 

[3 marks]

2b1 mark
b)
Since the original project, thousands of other DNA sequences have been recorded from a wide range of different people.

In early 2022 the world record for the fastest whole human genome sequencing was achieved. 

Scientists from Stanford University sequenced the whole human genome in 5 hours and 2 minutes. 

Why is it beneficial to collect the data as quickly as possible?
[1 mark]
2c3 marks
c)

As well as humans, scientists have sequenced the whole genome, or small sections of DNA, from thousands of different non-human species, such as bacteria, animals and plants. 

Explain why it is important to sequence the DNA of non-human species. 

[3 marks]

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3a3 marks
a)

Cystic fibrosis is an inherited condition. 

A cystic fibrosis sufferer's mucus becomes thick in their breathing system.

Figure 4 shows how, in a healthy person, cells at the lung surface move chloride ions into the mucus surrounding the air passages.

Figure 4

mucus-in-the-lungs-1

The movement of chloride ions causes water to pass out of the cells into the mucus.

Explain why.

[3 marks]

3b2 marks
b)
Figure 5 shows the inheritance of cystic fibrosis in one family.

Figure 5

pedigree-chart-example-1

Is cystic fibrosis caused by a dominant or recessive allele?

Use evidence from Figure 5 to support your answer. 

[2 marks]

3c5 marks
c)

Couple 5 and 6 from Figure 5 are Mr and Mrs Brown. 

Mr and Mrs Brown are hoping to have another child but are worried about the chance that the future child will have cystic fibrosis. 

They decided to visit a genetic counsellor who discussed embryo screening.

Read the information which they received from the genetic counsellor.

  • Five eggs will be removed from Mrs Brown's ovaries while she is under an anaesthetic.

  • The eggs will be fertilised in a dish using Mr Brown’s sperm cells.

  • The embryos will be grown in the dish until each embryo has about thirty cells.

  • One cell will be removed from each embryo and tested for cystic fibrosis.

  • A suitable embryo will be placed into Mrs Brown’s uterus and she may become pregnant.

  • Any unsuitable embryos will be destroyed.

Using your knowledge of cystic fibrosis and the information above, evaluate the use of embryo screening in this case.

Give a conclusion to your evaluation.

[5 marks]

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4a2 marks
a)
Red-green colour blindness is a genetically inherited condition that causes individuals with the condition to not be able to distinguish between certain colours. 

Red-green colour blindness is caused by a recessive allele located on the X chromosome. 

In order for a male to have the condition they only need to inherit one copy of the recessive allele on the X chromosome, whereas a female needs to inherit two copies of the recessive allele. 

Why is this the case?

[2 marks]

4b1 mark
b)
Using Figure 6, explain why it is possible for the X chromosome to have genes that are not found on the Y chromosome. 
[1 mark]
Figure 6
karyogram-showing-a-typical-karyotype-1
4c5 marks

Higher Tier Only

c)
A heterozygous woman and a colour blind man want to have a child.

Draw a Punnett square diagram to determine the probability of the child having colour blindness

Identify any children with colour blindness.

Use the following symbols:

XB = dominant allele on the X chromosome

Xb = recessive allele on the X chromosome

Y = Y chromosome (no colour blindness allele)

[5 marks]

 

Father

Mother

Parental phenotypes

_________________

_________________

Parental genotypes

_________________

_________________

Gametes

________  ________

________  ________

 

 

 

 

Offspring genotypes: _____________________________________________

Offspring phenotypes: ____________________________________________

4d
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4 marks
d)
8% of human males and 0.6% of females of Northern European ancestry suffer from red-green colour blindness. 

Out of a collection of 5 000 000 people from this ancestry, calculate the how many more men suffer from red-green colour blindness in comparison to women. 

Give your answer in standard form. 

[4 marks]

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1a2 marks

A child took a bite of a strawberry bought at a food market.

The child thought the strawberry tasted so good, she decided she wanted to grow her own strawberry plants from the remaining seeds from the strawberry.

She let the seeds germinate before planting them in her parent’s allotment.

The following summer, the plants grown from the seeds produced strawberries.

(a)

The child was disappointed that the strawberries grown in the allotment were not as large and didn’t taste the same as the strawberry from the market.

Explain why the strawberries grown by the child did not have the same characteristics as the market bought fruit.

[2 marks]

1b2 marks

(b)

Strawberries can naturally reproduce asexually by producing runners.

How does asexual reproduction differ from sexual reproduction?

[2 marks]

1c3 marks

(c)

Farmers can use an alternative method to produce strawberry plants that taste the same as the strawberries from a parent plant.

Describe and explain how it is possible for farmers to produce strawberries that are identical to the parent plant.

[3 marks]

1d2 marks

(d)

The type of cells formed by meiosis and mitosis differ.

Describe how.

[2 marks]

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2a3 marks

The skin is the largest organ of the human body.

Every 30 minutes, 0.03 g of skin is lost. 

(a)

Calculate how many kg of skin is lost by the average human in 365 days.

Write your answer in standard form.

[3 marks]

2b1 mark

(b)

Name the type of cell division that occurs in the skin to replace those cells that are lost.

[1 mark]

2c3 marks

(c)

In the average adult human male, sperm are continually produced in the testicles by a process known as spermatogenesis.

Every second, around 1500 new sperm cells are made.

Calculate how many sperm cells are produced by an average adult male in 365 days.

Write your answer in standard form.

[3 marks]

2d6 marks

(d)

Compare and contrast the type of cell division that occurs in the testes with that that occurs in the skin.

[6 marks]

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3a3 marks

Tay-Sachs disease is an inherited genetic disorder that results in the destruction of neurones in the brain and spinal cord.

Babies born with Tay-Sachs disease typically do not survive into childhood.

(a)

Two parents who do not have Tay-Sachs can still produce children who do have the disease.

Explain how children can inherit this disease from parents who are symptomless.

[3 marks]

3b3 marks

(b)

Tay-Sachs is more prevalent in certain communities.

A genetic test can reveal if a person carries the allele for Tay-Sachs.

A couple wish to have a child but they are both carriers of Tay-Sachs.

Suggest how modern technology could help the couple have a child without Tay-Sachs disease.

[3 marks]

3c1 mark

(c)

Many people object to using reproductive technology to help couples have children with or without certain characteristics.

Suggest one reason it might be considered acceptable to use technology to help a couple not have a child with a genetic disorder like Tay-Sachs.

[1 mark]

3d1 mark

(d)

At the moment, it is not acceptable to use reproductive technology to allow a couple to select the gender of their offspring.

Suggest one reason why.

[1 mark]

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42 marks

(a)

There are two types of cell division; mitosis and meiosis.

Explain why meiosis is not necessary in asexual reproduction.

[2 marks]

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