Cell Division in Eukaryotic & Prokaryotic Cells (AQA A Level Biology)

The death rate from malignant brain tumours was investigated in the UK. The graph in Figure 1 shows the results for women in different age groups.

Figure 1

Describe the relationship seen in the graph in Figure 1.

Give two possible explanations for the relationship seen in Figure 1.

There are two main forms of tumours (one being malignant tumours).

Benign tumours can still cause damage to the body. Describe two ways in which this can occur.

A student is confused by two similar terms they learnt about in class: ‘chromosome’ and ‘chromatid’. They can no longer remember the difference between the two terms. 

The student asks you for help.

A student writes the statements below describing the different stages in mitosis but is missing some information. 

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 ______,

Stage 3: ______, causing the chromatids to separate and move towards ______ .

Stage 4: A new nuclear membrane forms around each group of chromosomes.

Help the student by completing:

Compare what happens during cytokinesis in animal cells and plant cells.

Mitosis produces clones.

In simple biological terms, define what clones are.

Table 1 below shows features of meiosis and mitosis.

Table 1

Complete Table 1 with ticks (✔) where a feature is present.

The letters F, G, H, I and J represent the stages of mitosis.

F = interphase

G = prophase

H = metaphase

I = anaphase

J = telophase

Decide which one of the letters, F to J, the following statements refer to.

(iv)   DNA is replicated.

The diagram in Figure 1 shows two chromosomes in a cell undergoing mitosis.

Figure 1

Regarding the diagram in Figure 1:

After looking at the diagram in Figure 1, a scientist concludes that the two chromosomes in Figure 1 are homologous.

Use the diagram in Figure 1 to explain why the scientist has come to this conclusion.

Figure 1 shows a micrograph of cells in actively dividing tissue from the tip of a plant root.

Figure 1

ii)  Using Figure 1, complete Table 1

Table 1

Regarding Figure 1:

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

What stage of cell division are these cells in?

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

Calculate the mitotic index for this dividing root tissue.

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

When the student prepared the root tip squash in part c), the root tip was placed on a microscope slide with a stain.

Explain why a stain was used.

Explain how genetic variation is increased through meiosis.

The diagram in Figure 1 shows a cell cycle.

Figure 1

What does the part of the cell cycle labelled I in Figure 1 represent?

Skin cells complete the cell cycle in a short time.

Give one advantage of this.

The average time required for a human skin cell to complete the cell cycle is 2 hours 48 minutes.

Calculate the time required in minutes for one skin cell to multiply to produce 16 cells.Show your working 
.

During interphase in eukaryotic cells, DNA replication takes place. Explain why one strand of DNA replicates continuously, whereas the opposite strand replicates discontinuously. 

Some cell biologists believe that use of the term ‘cell division’ should be discontinued and replaced with ‘cell multiplication’. Evaluate this claim using your knowledge of the cell cycle.

A team of researchers estimated the numbers of cells in different stages of the cell cycle in healthy, growing onion plants. They took two tissue samples, A and B, from different parts of a plant. One tissue sample came from a root tip, the other from a large leaf near to the bottom of the plant’s stem. Their results are shown in Table 1.

Table 1

In tissue sample B, a full cell cycle took 20 hours and 45 minutes. Calculate the time, in minutes, that these cells were in telophase during one cell cycle. Show your working. 

Identify which tissue sample, A or B, was taken from the root tip. Use the information in Table 1 to explain your answer. 

Eukaryotes all possess a haploid number of chromosomes, denoted as n. The value of n varies from species to species. 

Chickens have n = 39.

Complete Table 1 below as it applies to chickens.

Table 1

A chicken has approximately 40% of the DNA of a human in its genome, whereas it possesses a higher haploid number of chromosomes (n = 39, versus n = 23 for humans). Explain this apparent contradiction. 

Describe and explain the factors that influence the duration of the cell cycle in multicellular organisms. 

The human genome contains 2.9 x 10⁹ base pairs. The S phase of a particular fast-growing cell type lasts 8 hours. Given that DNA polymerase has a replication rate of 40 nucleotides s^-1  enzyme  molecule^-1, calculate the number of DNA polymerase molecules in operation during S phase. State your answer to an appropriate number of significant figures. 

A researcher prepared a stained squash sample of cells from the tip of a garlic root. The first 3 mm of a root tip was cut off and stained on a microscope slide, before placing a coverslip on top of the sample and stain. She then examined the sample under a light microscope. 

During the sample preparation, the researcher pressed down on the sample tissue by applying pressure to the coverslip. Explain why this step was taken. 

The researcher drew a picture of what she could see in the field of view of the microscope. This is shown in Figure 1.

Figure 1

Using Figure 1, calculate the mitotic index of the garlic root tip tissue. 

This researcher’s colleagues calculated that the cell cycle of garlic root tips in growth is 1,320 minutes in length, and that on average, cells spend 4 hours in the visible stages of mitosis. 

Calculate the percentage difference between the data gathered by this researcher and the mean length of the mitotic stages found by her colleagues.

Compare and contrast the process of cytokinesis in animal and plant cells. 

The cell pictured in Figure 1 is undergoing the prophase stage of mitosis. Identify structures A, B and C and describe how they behave during prophase. 

Figure 1

Figure 2 shows the mortality rates in men of various age groups from prostate cancer in Europe from 1980 to 2015.

Figure 2

Describe and explain the overalls trend shown in Figure 2.

Using data from Figure 2, compare the percentage improvements in death rates between 1995 and 2015 in men of age groups 60-69 and men aged 80+. Suggest an explanation for the difference you have calculated. 

Relate the term, ‘metastasis’ with a person’s survival chances following the occurrence of metastasis. 

Figure 1 shows a scanning electron micrograph of a cell from the bacterial species Bacillus subtilis undergoing binary fission. 

Compare and contrast the processes of binary fission and eukaryotic cell division. Do not include references to meiosis in your answer. 

Under certain laboratory conditions, scientists grew a culture of Bacillus subtilis which was found to replicate once every 46 minutes. A small colony of cells was inoculated into a sterile nutrient broth which contained sufficient food, water and other nutrients to facilitate logarithmic growth of the bacterial cells. These cells entered a lag phase of one hour with no growth before growing logarithmically.

The scientists estimated a total cell count of 1.13 x 10¹³ cells 24 hours after inoculating the broth. Calculate the number of viable cells in the initial inoculum. Give your answer to 3 significant figures. 

Evaluate the claim that viruses are not living organisms. Use your knowledge of viral replication to support your answer. 

Gene therapy involves the introduction of functional genes into cells in place of genes that have become defective and non-functional. Explore the properties of viruses that make them a good candidate for gene therapy.