Practise › Questions › The cell cycle: growth, copying, and one division that changes nothing

The cell cycle: growth, copying, and one division that changes nothing questions

The cell cycle through G1, S and G2 to mitosis, the three checkpoints and what each one asks, chromosomes as chromatids after replication, the spindle, the four stages of mitosis in order, cytokinesis, the mitotic index calculation and the root tip practical behind it, binary fission in prokaryotes, and how uncontrolled division relates to tumour formation.

5 original questions · 17 marks · the cell cycle: growth, copying, and one division that changes nothing notes · Cell cycles, reproduction and development

Every question here is written for this library rather than taken from a past paper. Write your answer out before opening a mark scheme: the schemes award marks point by point, and the points are much easier to see when you have something of your own to compare against.

• 4 marks · Describe

  Describe what happens to the chromosomes during each of the four stages of mitosis, in the order the stages occur.

  Mark scheme

  1. B1 prophase: chromosomes condense and become visible, each already two sister chromatids
  2. B1 metaphase: chromosomes line up along the equator, attached to spindle fibres at their centromeres
  3. B1 anaphase: centromeres divide and the sister chromatids are pulled to opposite poles
  4. B1 telophase: chromosomes reach the poles, decondense, and a nuclear envelope re-forms around each group

• 4 marks · Explain

  Explain how a mutation in a tumour suppressor gene can lead to the formation of a tumour.

  Mark scheme

  1. B1 tumour suppressor genes normally halt the cell cycle at a checkpoint
  2. B1 a mutation can switch the gene off, so the protein it codes for is not produced or does not function
  3. B1 the checkpoint no longer stops cells with damaged DNA or incomplete replication from dividing
  4. A1 division continues unchecked and a mass of cells accumulates, which is a tumour

• 3 marks · Explain

  A cell from a mouse has 40 chromosomes. Explain why the cell still has 40 chromosomes at the end of G2, even though the quantity of DNA in it has doubled.

  Mark scheme

  1. B1 DNA is replicated during S phase, so each chromosome is copied
  2. B1 the two copies stay joined at a single centromere as sister chromatids
  3. A1 chromosome number is counted by centromeres, so it is unchanged at 40 while the DNA quantity is doubled

• 3 marks · Calculate

  A student counts 240 cells in a stained root tip squash and finds 36 of them are visibly in mitosis. Calculate the mitotic index, and give your answer as a proportion.

• 3 marks · Suggest

  A drug being tested as a cancer treatment binds to tubulin and prevents spindle fibres from forming. Suggest why this stops a tumour growing, and why the patient loses their hair.

Practise the cell cycle: growth, copying, and one division that changes nothing one question at a time

The player marks nothing for you. It shows one question, waits, then shows the scheme so you can mark yourself, and brings a question back sooner when it went badly.