Reproduction (Edexcel GCSE Biology: Combined Science)

The skin is the largest organ of the human body.

Skin cells are constantly undergoing cell division so that the outer dead cells are replaced.

Explain why the following statement does not accurately describe gametes (sex cells):

"Gametes are diploid cells produced by mitosis."

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

Explain why gametes need to be produced by meiosis and not mitosis

DNA is a polymer made from four different nucleotides.

Some students extracted DNA from strawberries using the following method:

1. In a beaker, gently mash up 50g of strawberries in soapy water
2. Place the beaker in a water bath at 60 °C for 15 mins
3. Filter the mixture into a boiling tube
4. Add two drops of protease enzyme
5. Slowly pour ice cold ethanol into the strawberry filtrate
6. Leave the tube for five minutes
7. Remove DNA with a glass stirring rod
   
   

Figure 1 shows the structure of a DNA nucleotide.

A scientist obtained a mass of 0.0062 nanograms of DNA from a diploid human cell.

Calculate the mass of DNA the scientist should obtain from a haploid human cell.

Give your answer in picograms.

(1 nanogram = 1000 picograms)

........................................ picograms

A student used the method shown in Figure 1 to compare the mass of DNA extracted from strawberry fruit cells and from kiwi fruit cells.

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Higher Tier Only

Transcription and translation are stages in the synthesis of proteins.

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Figure 2 shows a human egg cell, magnified ×700.

Figure 2

Calculate the actual width of the region indicated by the line on Figure 2.

Give your answer in millimetres, in standard form.

.............................................................. mm

James Watson and Francis Crick built a model that showed that DNA has a double helix structure.

Describe how this data provides evidence for base pairing in DNA.

Mitosis and meiosis are processes that produce new cells.

Compare the outcomes of mitosis and meiosis.

Figure 1 shows a strand of a molecule of DNA with the four bases represented by the letter A, B, C and D

Figure 1

The chain of bases shown in Figure 1 acts as a 'hypothetical' gene for the synthesis of haemoglobin. 

Higher Tier only

Higher Tier only

Figure 2 shows the partial DNA sequence of a gene that codes for a protein.

The coding strand and template strand are shown. 

Figure 2

Higher Tier only

Figure 3 shows the partial DNA sequence of a gene that codes for a normal functional protein.

There is a variant form of this gene that has a single base change from G to A as shown in Figure 3.

Normal sequence

Variant sequence

.

Figure 3

A scientist wanted to compare two different types of cell taken from a daffodil.

Complete Table 1 below to show the differences between the types of cells.

Put a tick (✓) in the relevant boxes.

Table 1

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Polyploidy is when a cell or organism has additional sets of chromosomes, along with the copies of chromosomes from the biological parents. This is a common phenomenon in plants.

Figure 1 shows an example of the effects of polyploidy in a strawberry plant. 

Figure 1

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Mitosis and meiosis are two types of cell division.

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Fern plants inhabit most continents on Earth. They are non-flowering plants and reproduce by producing spores. 

The diagram in Figure 1 shows some of the cell divisions that occur during fern reproduction. 

In the diagram, n represents haploid cells and 2n represents diploid cells.

Figure 1

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Figure 2 below shows Cell 1 undergoing meiosis. Stages of meiosis are similar to stages of mitosis. 

Figure 2

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In 2022, an estimated 6.4 million people in the UK smoked cigarettes regularly. 

The diagram in Figure 1 shows part of a DNA molecule of a non-smoker.

Figure 1

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The diagram in Figure 2 shows part of the same DNA molecule from the same individual after they smoked regularly for 20 years.

Figure 2

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Table 1 below shows data from research carried out in the UK to find out if smoking and alcohol use increased the likelihood of changes in DNA sequences. 79 male participants were tested for DNA changes.

The DNA sequence to be studied is found in the p53 protein, which is responsible for cell regulation during the cell cycle. When the protein is working normally it detects cells with damaged DNA and triggers a process called apoptosis which leads to cell death. .

Table 1

One scientist concluded that smoking and alcohol use increases the chances of cancer development.

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Blood at a crime scene can be tested for DNA.

Explain what type of blood cell the DNA might be found in.

DNA can be analysed to work out the order of some of the bases.

Figure 1 shows a base sequence taken from blood from a crime scene. There are three suspects in this case, and their base sequences are shown below.

The areas in black are where the base sequences match.

Figure 1

Suggest which suspect is most likely to have committed the crime. 

Explain your answer.

Research carried out by Watson and Crick contributed to the current understanding of the structure of DNA. One of the other main contributors towards this understanding was Rosalind Franklin, who managed to photograph an X-ray of a DNA molecule. 

This photograph, known as Photograph 51, is shown in Figure 2 below.

Figure 2

Franklin was able to determine the following from Photograph 51:

• The molecule had rounded corners
• The fuzzy borders of the structure vary in darkness
• There is an ‘X’ shape at the centre of the image
• There is a set distance between each of the repeating dashes

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The complete human genome was first mapped out in 2003 during the Human Genome Project.

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The flowchart in Figure 3 shows one method for extracting DNA from peas.

Figure 3

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