Cell & Nuclear Division (DP IB Biology: HL): Exam Questions

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

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

Explain why these homologous chromosomes are not identical.

Distinguish between the terms chromosome and chromatid.

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

State how Stage 2 and Stage 3 should be completed.

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. The student counted a total of 147 cells and determined that 95 of these cells were in various stages of mitosis.

(i) Calculate the student's mitotic index for this dividing root tissue.

[1]

The teacher wanted to double-check this. They found that:

• the student had counted the total number of cells correctly

• the mitotic index was actually 0.81

(ii) Calculate the number of cells that the teacher observed undergoing mitosis.

[1]

Brain cancer mortality was investigated in the UK. The graph below shows the results for women in different age groups.

Suggest a possible explanation for the relationship shown in the graph

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.

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.

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

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

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

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

Explain why the scientist reached this conclusion.

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 shown in the graph.

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

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

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

The drawing below shows a micrograph of actively dividing cells in tissue taken from the tip of a plant root.

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

In which of the cells (U, V, W, X, Y or Z) in the micrograph from (a) will the next event involve vesicles fusing to form new cell membranes.

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]

The diagram below represents the cell cycle.

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

Describe cytokinesis in animal cells and in plant cells.

Explain how the cell cycle is controlled.

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

The cell in the diagram is undergoing cell division.

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

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.

Use the formula 2ⁿ, where n = the number of pairs of chromosomes in a cell.

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

Chlamydosaurus kingii (Australian Frillneck lizard) is a diurnal lizard with a distribution that 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 frill length of 164 male lizards from two different sites 150 km apart.

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

Compare meiosis and mitosis by completing the table using yes / no or numbers.

The diagram below shows a cell undergoing cell division.

Explain how the process shown in the diagram will generate genetically different daughter cells.

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

Identify evidence that shows that the chromosomes are homologous.

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

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

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

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

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

An example of a condition that can result from an error during meiosis is Down syndrome. The table shows how the chance of having a baby with Down syndrome changes with maternal age.

Calculate how many times higher the chance of conceiving a baby with Down syndrome is for a 41-year-old mother compared with a 26-year-old mother.

Explain how genetic variation can be generated.

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

(i) Describe the change in chromosome number taking place during division I. 

(1)

(ii) Explain the importance of the change described in (i).

(1)

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.

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

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).

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

Outline the events that occur during anaphase I of meiosis.

Explain how random orientation contributes to genetic variation in gametes.

Compare and contrast meiosis II and mitosis.

Bowel cancer can develop from growths called adenoma polyps. These polyps form when mutations occur in the DNA of dividing cells in the lining of the colon.

Describe the cell cycle of a cancerous colon lining cell.

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

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

Suggest two conditions in which a cell might be prevented from passing through a checkpoint.

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.

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

During the cell cycle the cell passes through various checkpoints; one purpose of such checkpoints is to identify DNA copying errors. If an error cannot be repaired then the cell undergoes 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 exact stage of the cell cycle at which Pacilitaxel would take effect.

Biochemical analysis can be used to identify where the cell is in the cell cycle. One example of such analysis involves the application of radioactive thymidine to cells. Thymidine is a nucleotide precursor molecule.

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

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 cell samples, A and B, from cells grown in 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.

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

Estimate the time, in minutes, during which the cells in sample A were in S phase.

Use the formula:

time in phase = phase index total cell cycle time

Note that 'phase index' is equivalent to mitotic index, but uses the number of cells in any given phase rather than the number of cells undergoing mitosis.

Suggest, with a reason, which sample from part (a) was grown under nutrient-rich conditions.

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 collected from yeast in two sites which were deficient in nitrogen and phosphate.

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

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 how long DNA molecules are packed into yeast nuclei.

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

Calculate the mitotic index for this sample.

The cells shown in (a) had a cell cycle length of 26 hours and 20 minutes.

Estimate the length of time spent in mitosis for the root tissue cells shown in (a).

Use the formula:

time in mitosis = mitotic index total cell cycle time

Another student calculated the mitotic index using their root tissue sample, and came up with a different value.

Suggest why there may have been differences in the mitotic index between the students.

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.

Human papillomaviruses are the main cause of cervical cancer.

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

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

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

Annotate the graph in (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]

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

Identify processes that introduce variation at point X and at point Y.

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.

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

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

[1]

(ii) Explain your answer to (i).

[2]

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

[1]

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.

Distinguish between holocentric chromosomes and the monocentric chromosomes found in humans.

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.

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

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

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

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

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.

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 (i) and (ii) above.

[1]

Describe the roles of mitosis and meiosis in living organisms. Include named examples for each role.

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.

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]

Explain why meiosis is essential for sexual reproduction.

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.

Rotifers can be observed using an optical microscope.

Explain why this is the case.

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

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

(i) Stage X

[1]

(ii) Stage Y

[1]

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

The image below shows a diploid cell containing several chromosomes.

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

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.

Use the formula 2ⁿ, where n represents the number of pairs of chromosomes.

[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]

Describe the process of meiosis.

Explain the link between meiosis and evolution.

Note; details of the process of meiosis are not required.

Cells are said to be polyploid when they have more chromosomes than the normal diploid (2n) number. Polyploidy is considered to be a useful characteristic in crop plants because it often results in larger plants, and polyploid cells contain a wider range of alleles. Polyploidy can arise naturally, but it can also be induced with colchicine, a chemical that prevents microtubule formation in dividing cells.

Suggest how colchicine gives rise to tetraploid (4n) cells after mitosis in plants.

Plant scientists have been able to breed seedless watermelons by crossing tetraploid watermelons with regular, diploid plants to produce infertile, triploid (3n) plants.

The diagram below illustrates this process. Note that diploid watermelons contain 22 chromosomes.

Suggest why the offspring of the tetraploid-diploid cross are infertile.

A watermelon variety that naturally produces fewer seeds has been identified by scientists, and observation of its cells indicates that an event known as reciprocal translocation of chromosomes occurs in the cells of the watermelon variety. Reciprocal translocation of chromosomes involves the exchange of sections of chromosomes between non-homologous chromosomes during meiosis.

(i) Distinguish between reciprocal translocation of chromosomes and crossing over.

[1]

(ii) Suggest how reciprocal translocation of chromosomes could have resulted in a watermelon plant with a new phenotype.

[1]