Cell Division (Edexcel A (SNAB) A Level Biology)

Mitosis is an essential process for living organisms. 

Give two reasons why mitosis is so important.

Describe the appearance and behaviour of chromosomes during mitosis.

The diagram shows chromosomes at different stages of the cell cycle.

Of the cells in mitosis, place the stages in the correct order by completing the table below. The first stage has been done for you. 

A sample of tissue taken from a liver biopsy was analysed. Some of the cells had 6.4 units of DNA, others had only 3.2 units.

Explain the difference in DNA units of these cells.

One of the cells from the sample was analysed. The time required for the cell to complete one full cell cycle was 23 hours and 40 minutes. 

Calculate the time required for this cell to multiply to produce eight cells.

The graph below the the mass of DNA during the cell cycle

Use your knowledge of the cell cycle to explain the shape of the graph between:

5 and 8 hours

(1)

13 and 16 hours

(1)

Apart from an increase in the mass of DNA, give one process which occurs during hours 0 to 14 which enables nuclear division to occur.

Scientists investigated the effect of mitotic inhibitor drugs which prevent microtubule formation. One such drug is Vincristine; a chemotherapy drug that binds irreversibly to microtubules and spindle proteins in S phase of the cell cycle and interferes with the formation of the mitotic spindle.

The scientists found that Vincristine was effective at halting the cell cycle in both healthy and cancerous cells.

Explain why preventing the formation of spindle fibres stopped the cell cycle.

Explain why Vincristine can be used as a treatment for cancer even though it affects some healthy cells.

Vincristine was given to a cancer patient. It was given once every three weeks, starting at time 0.

The graph shows the changes in the number of healthy cells and cancer cells during twelve weeks of treatment.

Using the graph calculate the number of cancer cells present at week 12 as a percentage of the original number of cancer cells.

Describe two differences in the effect of Vincristine on cancer cells, compared with healthy cells.

Cells divide by mitosis to form new cells.

Describe the changes that occur within the cell between the beginning of prophase and the end of metaphase.

The diagram below shows a chromosome in a cell undergoing mitosis.

Identify structure P.

(1)

Describe the role of structure P during mitosis.

(1)

From the diagram in part (b): 

(i)

(1)

Explain why it is important for DNA replication to take place before mitosis can occur.