Syllabus Edition

First teaching 2023

First exams 2025

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Cell & Nuclear Division (HL IB Biology)

Exam Questions

6 hours91 questions
1a
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2 marks

The following diagram shows the arrangement of DNA in a eukaryotic chromosome.

GHxh5-Zo_e-4a

(i)

Label structure A in the diagram.

[1]

(ii)

State what is represented by the banding pattern on structure A.

[1]

1b
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2 marks

Use the information in the diagram in part a) to:

(i)

Identify structures B and C.

[1]

(ii)

Describe the relationship between structures B and C.

[1]

1c
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1 mark

Chromosomes in diploid cells will occur in homologous pairs.

Define the term 'homologous chromosomes'.

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2a
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1 mark

State the feature that forms in animal cells by the pinching of the plasma membrane during cytokinesis.

2b
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2 marks

Define the term mitosis

2c
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3 marks

The drawings below show a cell during different stages of mitosis.

1-4-e-1c-paper-2

 
List the stages P, Q, R, S and T in the correct sequence.

2d
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1 mark

Cell M contains 74 chromosomes. It divides by mitosis. 

State the number of chromosomes that will be present in the new daughter cells.

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3a
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1 mark

State the name of the group of proteins that control the cell cycle. 

3b
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1 mark

The diagram below represents the different phases of the cell cycle.

1-4-e-2b-paper-2

 State all the letters in the diagram that represent the phases of interphase.

3c
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1 mark

The tumour suppressor gene TP53 codes for a protein that interrupts the cell cycle if there is any damage to the DNA, preventing the copying of damaged DNA. 

State the stage of the cell cycle that would be interrupted by this protein.

3d
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2 marks

Define the term oncogene

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4a
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3 marks

The diagram below shows two different stages of mitosis.

1-4-e-3a-paper-2

Identify structures M, N and O.

4b
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3 marks

List three reasons why cells will undergo mitosis.

4c
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1 mark

State the name of the process that occurs during prophase that causes the chromosomes to become visible as separate structures.

4d
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2 marks

List two examples of mutagens.

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5a
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2 marks

The diagram below shows some grasshopper cells.

d2YSTw69_e-4a

Identify the stages of mitosis taking place in cells X and Y.

5b
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3 marks

Outline the events occurring during stage Z in part (a).

5c
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2 marks

The diagram below shows onion cells from a root tip.e-4c

Calculate the mitotic index for this root tip.

5d
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1 mark

Doctors use the mitotic index when examining tumours.

Suggest what a high mitotic index would indicate to a doctor.

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6
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6 marks

Budding yeast cells complete a cell cycle in 90 minutes.

Outline the stages in the cell cycle that result in the development of new yeast cells. 

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7a2 marks

Outline the purpose of meiosis in living organisms.

7b2 marks

The table below contains a series of statements about meiosis in human cells.

Statement True / False
2 daughter cells are produced False
Homologous pairs of chromosomes are separated  
Daughter cells have the full number of chromosomes  
Two cycles of division take place  
DNA replication occurs before the process begins  

Complete the table by indicating whether each statement is true or false. The first row has been completed for you.

7c2 marks

The diagram below shows a simplified life cycle of a fern plant.

1-6

Identify the types of cell division taking place at the positions marked A and B.

7d1 mark

Identify the process taking place at the position marked C in the diagram in part c).

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8a3 marks

The image below shows two chromosomes.

e-2c

(i)

Identify the structures labelled X and Y.

[2]

(ii)

Structures Y and are identical.

State why this is the case.

[1]

8b2 marks

The two chromosomes shown in part b) can be described as homologous chromosomes.

Define the term homologous chromosome.

8c1 mark

During meiosis the homologous chromosomes shown in part b) are separated.

Identify the stage of meiosis during which the homologous chromosomes are separated.

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9a1 mark

The image below shows a pair of chromosomes during meiosis.

mq3b

Identify the process taking place in the image.

[1]

9b2 marks

State the alleles that will be present on each of the grey shaded chromatids at the end of the process shown in part a).

9c2 marks

There are many different possible combinations of chromosomes that can be found in the daughter cells produced during meiosis.

Use the formula 2n to calculate the number of possible chromosome combinations that can be generated in domestic cat gametes. Note that the adult cells of domestic cats contain 38 chromosomes.

9d2 marks

Another source of variation during meiosis is a chromosome mutation that results from an event known as chromosome non-disjunction.

(i)

State the meaning of the term non-disjunction.

[1]

(ii)

Identify one factor that increases the risk of chromosome non-disjunction occurring during meiosis.

[1]

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10a1 mark

The diagram below summarises the processes of mitosis and meiosis.

3-3

Identify the process marked X in the diagram.

10b1 mark

Identify the stage of the cell cycle during which the process marked X in part a) takes place.

10c2 marks

Describe one way in which the process marked X in part a) can increase genetic variation.

10d2 marks

Describe the chromosome activity taking place at the stage marked Y in the diagram in part a).

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11a3 marks

The diagram below shows two chromosomes during meiosis.

crossing-over-structure-sq

Identify structures X, Y and Z.

11b3 marks

Outline the events shown in the diagram in part a).

11c3 marks

At the end of meiosis the chromosomes shown in part a) form four new chromosomes, as illustrated in the diagram below.

Annotate the four new chromosomes below to show the results of the events shown in part a). The first chromosome has been annotated for you.

chromosomes-after-crossing-over-sq

11d2 marks

Outline the importance of the process shown in part a) to living organisms.

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12a2 marks

The diagram below shows a cell in anaphase of meiosis I.

Meiosis anaphase I

State how it is possible to know the following:

(i)

That the cell is in anaphase.

[1]

(ii)

That the cell is in meiosis I.

[1]
12b1 mark

Meiosis I is described as reduction division.

State why this is the case.

12c2 marks

Meiosis I generates genetic variation due to the process of crossing over.

Outline one other process during meiosis I that generates genetic variation.

12d
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2 marks

Rice, Oryza sativa, has a chromosome number of 24.

Use the formula 2n to calculate the number of different chromosome combinations that can be generated when rice cells undergo meiosis I. Note that the term n here denotes the number of pairs of chromosomes.

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13a2 marks

The diagram below shows chromosomes from a garden pea plant, Pisum sativum, during meiosis.

mq5a

Identify, with a reason, the meiotic division that is occurring in the diagram.

13b2 marks

At the end of meiosis, the chromosomes were distributed to the pea plant pollen grains as shown below.

mq5b

Explain how the chromosomes in part a) gave rise to the new allele combinations shown above.

13c1 mark

The process in part b) and random orientation both contribute to genetic variation.

State one other process that contributes to genetic variation.

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143 marks

Draw an annotated diagram to show how crossing over takes place during meiosis.

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1a2 marks

Outline the process which leads to the production of a chromosome with the appearance shown in the image below.

biology-3-1-q1b-sq-ib-hl

1b2 marks

In meiosis I, homologous chromosomes pair up before being separated during the first division. 

Explain why these homologous chromosomes are not identical.

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2a2 marks

Distinguish between the terms chromosome and chromatid.

2b3 marks

The following statements contain information about the stages of mitosis, with some details missing.

Stage 1: Chromosomes become shorter and thicker, and the nuclear membrane breaks down.
Stage 2: Chromosomes line up along the equator of the cell and      (i)     ,
Stage 3:     (ii)     , causing the chromatids to separate and move towards      (iii)     .
Stage 4: A new nuclear membrane forms around each group of chromosomes.

Complete Stage 2 and Stage 3 with appropriate statements.

2c2 marks

The mitotic index is a measure of the proliferation status of a cell population (i.e. the proportion of dividing cells).

A student prepared a root tip squash and observed the cells under a microscope. A total of 147 cells were observed and 95 of these cells were observed in various stages of mitosis.

(i)

Calculate the mitotic index for this dividing root tissue.

[1]

The teacher wanted to double-check this. The student had counted the total number of cells correctly but the teacher calculated a mitotic index of 0.81.

(ii)

Calculate the number of cells that the teacher observed undergoing mitosis.

[1]

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3a1 mark

The death rate from brain cancer was investigated in the UK. The graph below shows the results for women in different age groups.

q2a-1-4-cells-division-medium-ib-hl-biology-sq

Suggest a possible explanation for the relationship seen in the graph above.

3b2 marks

Melanoma is a type of skin cancer that develops from pigment-producing cells in the skin known as melanocytes. Sun exposure is a risk factor in the development of melanoma.

Explain why sun exposure increases the risk of melanoma.

3c3 marks

There are two main forms of tumour, one of which is known as benign.

State the name of the other main form of tumour and outline two ways in which it differs from a benign tumour.

3d2 marks

Describe two ways in which both types of tumour may cause harm to the body.

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4a2 marks

The diagram below shows two chromosomes in a cell that is undergoing mitosis.

q3a-1-4-cells-division-medium-ib-hl-biology-sq

Identify structure Q and explain what happens to it during anaphase.

4b2 marks

After looking at the diagram in part (a), a scientist concludes that the two chromosomes are homologous.

Use the diagram in part (a) to explain why the scientist has come to this conclusion.

4c4 marks

A group of researchers investigated the relationship between the average number of cigarettes smoked by men per day and the number of men dying from colon cancer in 14 different countries. The data from the study is provided in the graph below.

q3c-1-4-cells-division-medium-ib-hl-biology-sq

A website reported the results of this investigation using the headline ‘Smoking causes cancer’.

Explain why the researchers could not support this view based on the results of their investigation alone.

4d2 marks

Explain why the death rate from colon cancer in part (c) is given per 100 000 men and not given as the total number of deaths.

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5a3 marks

The drawing below shows a micrograph of actively dividing cells in tissue taken from the tip of a plant root.q4a-1-4-cells-division-medium-ib-hl-biology-sq

Complete the table to identify the stage of cell division visible in cells W, V and Z.

Cell Stage of cell division
W  
V  
Z  
5b1 mark

In which of the cells (U, V, W, X, Y or Z) in the micrograph drawing in part (a) can vesicles now fuse to form new cell membranes across the cytoplasm (in order to separate the cell into two daughter cells).

5c3 marks

Tumour-suppressor genes are a group of genes that are involved in the control of cell division.

(i)

Identify another type of gene that is involved in regulating cell division

[1]

(ii)

Explain why a mutation in this type of gene can lead to cancer

[2]

5d2 marks

The diagram below shows a cell cycle.

q4d-1-4-cells-division-medium-ib-hl-biology-sq

Explain what occurs during the part of the cell cycle labelled I.

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6a3 marks

Describe cytokinesis in animal cells and in plant cells.

6b5 marks

Explain how the cell cycle is controlled.

6c7 marks

Describe the events that take place during mitosis, including the name of the stage of mitosis during which each event occurs.

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7a2 marks

Identify, with a reason, the type of cell division shown in the diagram

biology-q1a-sq-ib-hl-3-2

7b1 mark

Pisum sativum (garden pea) has a diploid chromosome number of 14. 

Calculate the number of different chromosome combinations can result during meiosis, assuming no crossing over occurs.

7c2 marks

Discuss the significance of meiosis in the life cycle of Pisum sativum (garden pea).

7d2 marks

Chlamydosaurus kingii (Australian Frillneck lizard) is a diurnal (active during the day) lizard whose distribution extends across northern Australia and into Papua New Guinea. If the lizard is startled it opens its mouth and flexes the muscles in its frill (a large fold of skin surrounding its throat) causing it to be raised. Scientists believe that the frill is used to deter predators and to attract females. 

The graphs below show the variation in the frill length of 164 male lizards from two different sites 150 km apart.

biology-3-2-q1d-sq-ib-hl

Explain how meiosis may have caused the variation shown in these graphs.

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8a2 marks

Complete the table using ‘yes’ / ‘no’ or numbers to compare mitosis and meiosis.

Feature Meiosis Mitosis
Number of nuclear divisions    
Number of daughter cells produced    
Genetically different daughter cells are produced    
Crossing over occurs    
Homologous chromosomes pair up    
8b2 marks

Explain how the diagram below illustrates that the resulting daughter cells will be genetically different. Give evidence from the diagram to support your answer

biology-3-2-q2b-ib-hl-sq

8c2 marks

The diagram below shows a pair of chromosomes during meiosis in a cell in a Drosophila melanogaster (fruit fly) testis. The position of the alleles of some genes is indicated.

biology-3-2-q2c-sq-ib-hl

Explain whether the chromosomes are homologous or non-homologous.  

8d3 marks

At the end of meiosis, each of the chromosomes shown in the diagram from part (c) will be in a different haploid cell.

biology-q2d-3-2-sq-ib-hl

Label the diagram above to show the combinations of alleles that would be present on each chromosome inside the haploid daughter cells.

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9a1 mark

The diagram shows the chromosomes found in a parent cell and the daughter cells produced after meiosis

biology-3-2-q3a-sq-ib-hl

Identify the daughter cell(s) that contain a chromosome mutation by circling the cell(s).

9b2 marks

Explain how the spontaneous chromosome mutation shown in part (a) arose in the daughter cells during meiosis. 

9c1 mark

The risk of a non-disjunction mutation increases with age. The table shows how the Down syndrome risk increases with age.

Mothers Age (Years) Chance of conceiving a baby with Down syndrome
25-29 1 in 1250
30-34 1 in 1000
35-39 1 in 400
40-44 1 in 100
45+ 1 in 30

Calculate how much more likely it is that a child is conceived with Down Syndrome for a mother who is 41 compared to a mother who is 26.

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10a1 mark

The diagram below shows the life cycle of Calvatia gigantea (giant puffball). In this life cycle, only the zygote and mature puffball are diploid. All the cells in all the other stages of the life cycle of the puffball are haploid, including the spores.

biology-q4a-ib-hl-sq-png

Identify which letter in the diagram shows where meiosis occurs in the life cycle of Calvatia gigantea

10b4 marks

The micrographs below show cells undergoing meiosis.

biology-q4b-3-2-ib-hl-sq

Identify, with a reason, the stages of meiosis shown in each micrograph.

10c2 marks

A Pisum sativum (garden pea) pollen cell is undergoing meiosis. During the initial phase of meiosis a pair of homologous chromosomes located in these cells can be represented by the chromosomes shown below. The two different letters represent two different genes.

biology-3-2-q4c-sq-ib-hl

At the end of meiosis the chromosomes were distributed to the four pollen grains as shown in the gametes below.

Figure 2biology-3-2-q4c2-sq-ib-hl-png

Describe how the new allele combinations seen in these gametes were formed during meiosis. 

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117 marks

Explain how genetic variation can be generated.

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12a2 marks

The following image shows a cell undergoing cell division.

q1a_10-1_meiosis_medium_ib_hl_biology_sq
 

Identify, with a reason, the type of cell division shown in the image.

12b2 marks

The image below illustrates the formation of sperm cells, also known as spermatozoa.

q1b_10-1_meiosis_medium_ib_hl_biology_sq

State and explain the change in chromosome number taking place during division I

12c2 marks

A sperm-producing cell in the testes has 46 chromosomes in its nucleus.

Calculate the number of chromatids that would be in the nucleus of this cell after it has undergone meiosis I.

12d2 marks

Outline the first steps in the process of meiosis, known as prophase I.

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13a2 marks

The diagram below shows a homologous pair of chromosomes from a parent cell (top) and two gamete nuclei that form at the end of meiosis (bottom).

q2b_9-2_transport_in_the_phloem_of_plants_medium_ib_hl_biology_sq

Draw the chromosomes present in each of the indicated gamete nuclei at the end of meiosis. Consider both shading and alleles in your answer.

13b2 marks

Outline the events that occur during anaphase I of meiosis.

13c2 marks

Explain how random orientation contributes to genetic variation in gametes.

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14a2 marks

European rabbits (Oryctolagus cuniculus) have a diploid (2n) chromosome number of 44.

The number of possible chromosome combinations that are possible as the result of random orientation can be calculated using the formula 2n, where n is the haploid chromosome number.

Calculate the number of different possible chromosome combinations in the gametes of rabbits.

14b2 marks

The graph below shows how the mass of DNA changes over time during two different types of cell division in a diploid organism.

q3b_10-1_meiosis_medium_ib_hl_biology_sq
Identify, with a reason, which of the division types represents meiosis.

14c2 marks

Describe the processes represented by the letters X and Y in the graph in part b).

14d2 marks

The fruit fly (Drosophila melanogaster) has a diploid number (2n) of 8.

The image below shows some cells from different organisms undergoing cell division.

q3d_10-1_meiosis_medium_ib_hl_biology_sq

   

Identify, with a reason, the cell which would represent a fruit fly cell that has just completed meiosis I.

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155 marks

Compare and contrast meiosis II and mitosis.

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1a
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2 marks

Bowel cancer can result from adenoma polyps. Adenoma polyps form as a result of mutations in the DNA of dividing cells in the colon lining.

Describe the cell cycle of a cancerous colon lining cell.

1b
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3 marks

Compare and contrast the process of cytokinesis in plants and animals.

1c
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2 marks

Before the cell progresses from G1 into S phase, it needs to pass through a checkpoint which prevents the cell cycle from proceeding if certain conditions are not met. 

Suggest two reasons why a cell might be prevented from dividing when it passes through a checkpoint.

1d
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2 marks

The graph below shows the number of cells that contain DNA bound to a fluorescent dye. The stages of the cell cycle are indicated on the x axis.

1-4-h-1d-paper-2

Suggest why, during the S phase, that the amount of DNA per cell is between 2n and 4n.

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2a
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2 marks

During the cell cycle there are various checkpoints the cell passes through; one purpose of such checkpoints is to identify DNA copying errors. If an error cannot be repaired then the cell goes through cell death (apoptosis).

Scientists have developed cancer drugs that can inhibit the cell cycle and cause the cell to carry out apoptosis. Paclitaxel and 5-fluorouracil are two of these cancer drugs.

  • Paclitaxel binds to spindle microtubules, preventing the spindle from performing its function
  • 5-fluorouracil prevents the synthesis of thymine nucleotides

Determine the stages of the cell cycle at which these drugs would take effect.

2b
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2 marks

Biochemical analysis can be used to identify where the cell is in the cell cycle, e.g. radioactive thymidine can be applied to cells. 

Suggest, with a reason, the phase that can be identified using radioactive thymidine.

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3a
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2 marks

A team of biologists estimated the number of cells in different phases of the cell cycle in Saccharomyces cerevisiae (brewer's yeast).

They took two samples, A and B, from different environmental conditions. One sample came from a nutrient-rich environment, the other from a nutrient-poor environment.

Their results are shown in the table below.

Phase of the cell cycle
Sample A 
/ number of cells counted
Sample B 
/ number of cells counted
G1
312
451
S
203
294
G2
136
196
Mitosis
27
39
Total
678
980

In sample A a full cell cycle took 1 hour and 35 minutes, whereas, in sample B a full cell cycle took 60 minutes. 

Calculate the time, in minutes, during which the cells in sample A were in S phase. Show your working.

3b
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2 marks

The biologists studying the Saccharomyces cerevisiae from part (a) hypothesised that when the yeast was exposed to stressful conditions, the growth rates were low. 

Suggest, with a reason, which sample came from the nutrient-rich conditions.

3c
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2 marks

The availability of nutrients is also a key factor in regulating the cell cycle of Schizosaccharomyces pombe (fission yeast).  Below is a table containing data scientists collected from yeast in two sites which were deficient in nitrogen and phosphate. 

Phase of the cell cycle Deficient in nitrogen / number of cells counted Deficient in phosphate / number of cells counted
G1 207 181
S 135 118
G2 90 79
Mitosis 0 0
Total 432 378

Deduce, with a reason, the point at which a nutrient-poor environment would arrest the cell cycle of the Schizosaccharomyces pombe.

3d
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2 marks

The Saccharomyces cerevisiae nuclei are, on average, 2 µm in diameter, but the DNA molecules packed into them can be up to 355 µm in length. 

Describe the process that enables the DNA molecules to be packed into the nuclei.

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4a
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2 marks

The diagram below shows a sample of root tissue collected by a researcher. The sample shows 74 cells in total.

Root tip mitotic index question

Calculate the mitotic index for this sample.

4b
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2 marks

A student’s research determined that the cell cycle in a similar root to that shown in part (a) was 1 560 minutes in length, and that on average, cells spent 5 hours in the visible stages of mitosis.

Calculate the percentage difference between the data gathered by the student and the mean length of the mitotic stages found by the researcher in part (a).

4c
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2 marks

Suggest two possible reasons why there may have been differences in the mitotic index the researcher determined and the student’s value.

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5a
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4 marks

MPXV is a virus that belongs in the same group as smallpox and cowpox.

Explain why viruses, such as MPXV, do not have a cell cycle.

5b
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3 marks

Some cell biologists believe that the use of the term ‘cell division’ should be discontinued and replaced with ‘cell multiplication’.

Evaluate this claim using your knowledge of the cell cycle.

5c
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6 marks

Human papillomaviruses are the main cause of cervical cancer.

Explain how mutagens, such as viruses, can interrupt the cell cycle to cause cancer.

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6a3 marks

The graph below shows changes in the mass of DNA over the course of a cell cycle.

meiosis-mass-of-dna-graph-sq

Explain the role of the process, represented by this graph, in living organisms.

6b3 marks

Annotate the graph in part a) to show the approximate points at which the following events are taking place:

(i)

G2

[1]

(ii)

Cytokinesis I

[1]

(iii)

Metaphase II

[1]

6c2 marks

Variation is introduced at the points labelled X and Y in the graph in part a).

Identify processes that could introduce variation at points X and Y.

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7a1 mark

The diagram below illustrates the life cycle of the pea aphid, Acyrthosiphon pisum. Note that the term autosome refers to any chromosome that is not a sex chromosome.

aphid-life-cycle-sq

Identify the biological sex of the individuals labelled P and Q.

7b4 marks

The diagram in part a) shows that aphids use a different type of reproduction in the spring and summer to the type used in the autumn.

(i)

Identify the type of reproduction used by aphids in the spring and summer, and in the autumn.

[1]

(ii)

Explain your answer to part i).

[2]

(iii)

Suggest the advantage to the aphids of switching their method of reproduction in the autumn.

[1]

7c2 marks

Most eukaryotic chromosomes are described as being monocentric. Aphids have unusual chromosomes known as holocentric chromosomes. A holocentric chromosome after DNA replication is shown in the diagram below.

chromosome-structure-aphid-holocentric-sq

Contrast holocentric chromosomes with normal monocentric chromosomes.

7d4 marks

While scientific understanding of aphid meiosis is still limited, the holocentric nature of their chromosomes means that aphids are thought to carry out a form of meiosis known as inverted meiosis. The possible behaviour of a homologous pair of aphid chromosomes during metaphase I is shown in the diagram below.

-iDx-gkr_inverted-meiosis-homologous-pairs-crossing-over-sq

Suggest, with reasons, two ways in which meiosis in aphids might be different to conventional meiosis.

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8a3 marks

The spider mite Eutetranychus africanus has very few chromosomes (2n = 4).

The diagram below shows a series of cells undergoing cell division.

q3d_10-1_meiosis_medium_ib_hl_biology_sq

Identify, with reasons, which of the cells in the diagram above belong to E. africanus.

8b
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3 marks

A sample of cells was taken from the reproductive organs of E. africanus and the mass of DNA in each cell was determined. Some of the cells’ DNA had a mass of 1.7 arbitrary units (a.u.) whilst other cells' DNA had a mass of 3.4 or 6.8 a.u..

Use your knowledge of the cell cycle to explain this observation.

8c3 marks

A species of false spider mite, Brevipalpus phoenicis, is the only animal to have so far been identified as having exclusively haploid cells throughout its life cycle. B. phoenicis populations are entirely female, producing eggs which hatch into more females.

The discovery of the haploid nature of B. phoenicis was a surprise to scientists, who believed that being diploid was essential due to the evolutionary advantage that it provides.

(i)

Identify the type of cell division by which B. pheonicis produces eggs.

[1]

(ii)

Suggest why scientists might think that diploidy provides an evolutionary advantage.

[1]

(iii)

B. phoenicis is a highly successful pest of citrus, tea, and palm plantations. Suggest how B. phoenicis might have evolved to become such a successful pest despite the points covered in parts i) and ii) above.

[1]

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9a3 marks

The diagram below shows three cells in different stages of cell division. Note that all of the cells shown have the same 2n chromosome number.

gene-loci-drosophila-mendelian-ratios-crossing-over-sq

Identify the cell(s) in the diagram above that show the following:

(i)

Homologous chromosomes

[1]

(ii)

Meiosis

[1]

(iii)

Reduction division

[1]

9b
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2 marks

Fruit flies, Drosophila melanogaster, are frequently used in scientific studies. The diagram below shows the gene loci and alleles of two genes on a pair of chromosomes in a male and female D. melanogaster individual. Note that the dominant alleles are long legs and red eyes.

314f7eef-f727-43d6-b876-d08e09ce2d77

A cross was carried out between the two individuals shown above. The table below shows the number of offspring with short/long legs and brown/red eyes produced from the cross.

Characteristics Number of offspring
Short legs and brown eyes 545
Long legs and red eyes 182
Short legs and red eyes 14
Long legs and brown eyes 12

Calculate the offspring ratios for the cross shown. Give your answers to the nearest whole number.

9c3 marks

Explain the offspring ratios shown in part b).

9d2 marks

The diagram below shows the gene loci and alleles for a third gene on the chromosomes of the individuals in part b). Note that the grey body allele is dominant to the black body allele.

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Suggest, with a reason, how the numbers of offspring with short/long legs and black/grey bodies would differ from the numbers with short/long legs and brown/red eyes shown in part b).

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106 marks

Use named examples to describe the roles of mitosis and meiosis in living organisms.

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11a4 marks

Rotifers are multicellular, aquatic animals that range in size from 50 μm to 3 mm. Their reproduction can be either asexual, resulting in the production of genetically identical females, or sexual, resulting in the production of eggs that can remain dormant for many years. A representation of a rotifer life cycle is shown in the diagram below.ph4-WAAe_h-1a

Annotate the diagram as follows:

(i)
Use the letter A to indicate one location within the asexual phase where mitosis is occurring.

[1]

(ii)

Use the letter B to indicate one location within the sexual phase where mitosis is occurring.

[1]

(iii)
Use the letter C to indicate two locations where meiosis is occurring.

[1]

(iv)

Use the letter D to indicate one location where fertilisation is occurring.

[1]

11b2 marks

Explain why meiosis is essential for sexual reproduction.

11c3 marks

Rotifers mainly reproduce asexually, switching to sexual reproduction for brief periods. The X in the diagram in part a) indicates the occurrence of a stimulus that shifts the rotifers from asexual to sexual reproduction. This stimulus could be a change in the environmental conditions, such as a drought that reduces the size of their habitat.

Use the information provided here and in part a) to explain why it is advantageous to rotifers to switch to sexual reproduction when environmental conditions change.

11d1 mark

Rotifers can be observed using an optical microscope.

Explain why this is the case.

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12a2 marks

The graph below shows how the mass of DNA changes over time during two different types of cell division in a diploid cell.

PIC42T3s_7

State what is happening at the following stages in the graph:

(i)

Stage X

[1]

(ii)
Stage Y

[1]

12b2 marks

Use the information provided in the graph in part a) to state, with a reason, which of the division types represents meiosis.

12c2 marks

The image below shows a diploid cell containing several chromosomes.

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Draw the possible appearance of four different gametes that could be produced from this diploid cell during meiosis.

12d
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3 marks

A diploid cell contains 26 chromosomes.

(i)

Calculate the number of different combinations of chromosomes that could be generated when this cell divides by meiosis.

[1]

(ii)

Explain why the number calculated in part i) is not a true representation of the amount of genetic variation that can be generated from this cell during sexual reproduction.

[2]

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13a8 marks

Describe the process of meiosis.

13b5 marks

Explain the link between meiosis and evolution.

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