Cell & Nuclear Division (HL IB Biology)

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.

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.

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.

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.

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.

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. 

Deduce, with a reason, the point 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 the process that enables the DNA molecules to be packed into the 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.

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).

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

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.

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.

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 this graph, in living organisms.

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

G2

[1]

Cytokinesis I

[1]

Metaphase II

[1]

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.

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.

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

[1]

Explain your answer to part i).

[2]

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.

Contrast holocentric chromosomes with normal monocentric chromosomes.

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.

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

[1]

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

[1]

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]

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.

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

Homologous chromosomes

[1]

Meiosis

[1]

Reduction division

[1]

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.

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.

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

Explain the offspring ratios shown in part b).

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.

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).

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

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:

[1]

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

[1]

[1]

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:

Stage X

[1]

[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.

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

[1]

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.

Distinguish between the terms chromosome and chromatid.

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

Complete Stage 2 and Stage 3 with appropriate statements.

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.

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.

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

[1]

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

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

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.

Describe 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 explain what happens to it during anaphase.

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.

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.

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.

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.

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 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).

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

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 shows a cell cycle.

Explain 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.

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.

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

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.

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

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

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

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.

Explain whether the chromosomes are homologous or non-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 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. 

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

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.

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.

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

The micrographs below show cells undergoing meiosis.

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

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.

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

Figure 2

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

Explain how genetic variation can be generated.

The following image shows a cell undergoing cell division.

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

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

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

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.

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.

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

Identify, with a reason, which of the division types represents meiosis.

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

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

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

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

Compare and contrast meiosis II and mitosis.