The cell cycle and mitosisAQA A-Level Biology: Subtopic test

1. 1
   A student prepared a stained squash of onion root tip cells and examined it with an optical microscope. In one field of view she counted 180 cells, of which 27 were in one of the stages of mitosis.

   (a)

   One cell in the squash showed chromosomes, each made of two chromatids, lined up across the centre of the cell. Which stage of mitosis was this cell in?

   [1 mark]

   • AProphase
   • BMetaphase
   • CAnaphase
   • DTelophase

   (b)

   What is the mitotic index of the root tip squash?

   [1 mark]

   • A0.15
   • B0.18
   • C6.7
   • D0.85

   (c)

   Explain why the student used the tip of the root, and why she squashed the stained tissue.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A cell biologist is studying a human skin cell that has 46 chromosomes in its nucleus before it divides by mitosis.

   (a)

   How many chromatids does this cell contain at metaphase?

   [1 mark]

   • A23
   • B46
   • C184
   • D92

   (b)

   What happens to the centromeres at the start of anaphase?

   [1 mark]

   • AThey fuse so that sister chromatids join together
   • BThey are digested by enzymes in the cytoplasm
   • CThey divide, allowing the sister chromatids to separate
   • DThey attach the chromosomes to the nuclear envelope

   (c)

   Explain how the sister chromatids of this cell are moved to opposite poles during anaphase.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A pharmaceutical company is testing a new drug on cultured tumour cells. The drug stops spindle fibres from forming, but it does not affect DNA replication. A technician counted cells in samples before treatment and 24 hours after treatment.

   (a)

   Explain how the drug would reduce the growth of a tumour.

   [3 marks]

   (b)

   Before treatment, 48 of 400 cells counted were in mitosis. After 24 hours, 124 of 400 cells counted were in mitosis, mostly in metaphase. Calculate the mitotic index after 24 hours and explain why it is higher than before treatment, even though the drug stops cells dividing.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A researcher is comparing a sample of tissue from a human tumour with healthy tissue from the same organ. The cells in both samples divide by mitosis.

   (a)

   Describe the behaviour of the chromosomes in interphase and during each stage of mitosis, and explain why the daughter cells are genetically identical to the parent cell.

   [6 marks]

   (b)

   Explain how uncontrolled cell division leads to the formation of a tumour, and evaluate cancer treatments that are directed at controlling the rate of cell division.

   [6 marks]

   Total for question 4: 12 marks

End of questions