Reproduction (Edexcel GCSE Biology)

State two advantages and two disadvantages of asexual reproduction.

Many plants such as strawberry plants grow runners that are special stems that grow out from the adult plant. New plants grow on these 'runner' stems.

The new plants will all have the same inherited characteristics of the original parent plant.

Use words from the box to complete the following statements.

(1) The  ________ plants are produced by ________ reproduction

(2) In this type of reproduction,  ________ cells divide by ________ 

(3) The new plants have the same ________ as the ________ plants

Hydra are small water animals that can reproduce through both sexual and asexual reproduction.

Figure 1 shows a Hydra in various stages of asexual reproduction.

Figure 1

(i) Explain why the offspring in Figure 1 (stage 4) will be genetically identical to the parent.

(3)

(ii) Hydra reproduces asexually when conditions are favourable to do so. If conditions change and become unfavourable they will switch to sexual reproduction.

Explain how the ability to reproduce both asexually and sexually helps Hydra to survive.

(3)

Describe some of the differences between sexual and asexual reproduction.

Describe some natural methods of cloning in eukaryotes.

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.

(i) State the type of cell division that occurs in skin cells to replace those cells that are lost.

(1)

(ii) 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)

(iii) State the type of cell division that produces mature sperm cells

(1)

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.

(i) Describe the components of a nucleotide.

(1)

(ii) State which term is used to describe the shape of DNA.

(1)

(iii) Describe how the structure of DNA results from 'complimentary base pairing'.

(3)

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

(i) Suggest why the protease solution was added in step 4.

(1)

(ii) Suggest why ethanol was added in step 5.

(1)

(iii) Strawberries are octoploid which means they have eight complete sets of chromosomes.

Suggest why this is beneficial in this type of experiment.

(1)

Figure 1 shows the structure of a DNA nucleotide.

Figure 1

(i) Structure A is a

(1)

(ii) In 2003, the first complete human genome was sequenced.

The genomes of different people have small changes in the sequence of the DNA bases.

Describe how these changes in DNA sequence can affect the individuals and how sequencing a person’s genome could influence their medical treatments.

(6)

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.

Figure 1

(i) State why ethanol is used.

(1)

(ii) State two variables the student needs to control when using this method to compare the mass of DNA from these two fruits.

(2)

1...........................................
2...........................................

(iii) The student repeated the experiment.

Give one reason why.

(1)

Higher Tier Only

Transcription and translation are stages in the synthesis of proteins.

(i) Which enzyme is involved in the process of transcription?

(1)

(ii) Describe how a mutation in the non-coding region of the DNA can prevent a gene being transcribed.

(2)

Discuss the advantages and disadvantages of sexual reproduction and asexual reproduction.

Figure 1 shows a sperm cell.

Figure 1

Describe how structure A and structure B enable fertilisation.

structure A........................................

structure B.........................................

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.

(i) Which statement about DNA is correct?

(1)

(ii) Figure 1 shows the percentage of each base in human DNA.

(2)

Figure 1

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. 

(i) Describe what a gene is.

(1)

Higher Tier only

(ii) Explain how the chain of bases shown in Figure 1 leads to the production of haemoglobin in the cell.

(6)

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

(i) Explain how many amino acids this partial sequence codes for.

(2)

(ii) State what the sequence of bases would be in the complementary mRNA strand.

(1)

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

(i) State another term that can be used to describe the change in base sequence.

(1)

(ii) State two factors that can lead to such changes in the base sequence of DNA.

(2)

(iii) Explain why the base change could result in a non-functioning protein.

(2)

The daffodil (Narcissus pseudonarcissus) is a well known native plant to many parts of the UK. 

Daffodils can reproduce in two ways:

• Asexually by cloning their bulbs

• Sexually through the process of pollination

(i) Explain why it is an advantage to the daffodil to be able to reproduce sexually.

(2)

(ii) Suggest why gardeners who grow daffodils might see the process of asexual reproduction as an advantage.

(2)

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

(i) A student was investigating mitosis in the root of a daffodil plant.

Describe how the student could prepare a microscope slide to show mitosis in the growing roots of the plant.

(4)

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

(i) Suggest how polyploidy could have arisen in a strawberry plant

(2)

(iii) Suggest what advantages polyploidy might have to crop growers.

(1)

Mitosis and meiosis are two types of cell division.

(i) State the stage of the cell cycle during which DNA replication occurs.

(1)

(ii) Explain why DNA replication is an important part of the cell cycle.

(1)

(iii) Describe three differences between the processes of mitosis and meiosis.

(3)

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

(i) Once a sporophyte has been formed, the cycle starts again.

Name the type of cell division that would form cell A from cell D in order to restart the process.

(1)

(ii) Explain the evidence from Figure 1 that led to the answer given in part (i)

(1)

(iii) Cell C contains 720 chromosomes.

Calculate how many chromosomes cell B has.

(1)

(iv) Explain why it is important that cell B has the number of chromosomes you stated in part (iii).

(2)

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

Figure 2

(i) Suggest what stage of meiosis Cell 1 is in.

(1)

(ii) Explain your answer to part (i)

(2)

(iii) Explain how meiosis contributes to genetic variation and suggest why variation is important.

(4)

Higher Tier Only

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

(i) Write the complementary base code for this section of mRNA in the boxes below.

(2)

(ii) State the maximum number of amino acids that could be coded for by this strand of DNA.

Explain your answer.

(2)

Higher Tier Only

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

(i) Explain why the DNA molecule in Figure 2 is different to the DNA molecule in Figure 1.

(2)

The molecule of DNA in Figure 2 codes for an enzyme involved in the process of cell division.

(ii) Explain how the change you described in (i) could affect the process of cell division.

(3)

Higher Tier Only

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.

(i) Evaluate this conclusion. 

(4)

(ii) Explain how a mutation in the p53 protein might result in the development of cancer.

(3)

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

(i) Suggest what information about the structure of DNA Franklin was able to conclude from Photograph 51.

(3)

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

(ii) Explain how the Human Genome Project has contributed to advances in medicine.

(3)

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

Figure 3

(i) Explain why salt is needed for the DNA extraction process.

(1)

(ii) Explain why ethanol is added in Step 5.

(1)

(iii) Explain how protease enzymes work to break down proteins.

(3)