Mitosis and the cell cycleEdexcel International A Level Biology: Subtopic test

1. 1
   A student prepares a squash from the tip of an onion root and views it under a light microscope. She sees many cells in different stages of the cell cycle.

   (a)

   During which phase of the cell cycle is DNA replicated?

   [1 mark]

   • AProphase
   • BS phase of interphase
   • CMetaphase
   • DTelophase

   (b)

   In one cell she sees the sister chromatids of each chromosome separated and being pulled towards opposite poles of the cell. Which stage of mitosis is this?

   [1 mark]

   • AProphase
   • BMetaphase
   • CTelophase
   • DAnaphase

   (c)

   The student cut only the first 1–2 mm from the root tip rather than a section from the middle of the root. Explain why.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student counted the cells in several fields of view of a stained root tip squash. In total she counted 320 cells, of which 48 were in mitosis and the remainder were in interphase.

   (a)

   What is the mitotic index?

   [1 mark]

   • AThe proportion of cells in a sample that are undergoing mitosis
   • BThe time taken to complete one cell cycle
   • CThe number of chromosomes in a cell during metaphase
   • DThe proportion of cells in a sample that are in interphase

   (b)

   What is the mitotic index of the sample?

   [1 mark]

   • A0.18
   • B6.7
   • C0.15
   • D0.85

   (c)

   Explain why most of the cells counted were in interphase.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates the effect of a chemical on cell division in garlic root tips. She grows one set of roots in water (root tip A) and another set in a solution of the chemical (root tip B), then examines a root tip squash of each with a light microscope. In root tip A she counted 450 cells, of which 63 were in mitosis. In root tip B she counted 380 cells, of which 19 were in mitosis.

   (a)

   Describe how the student should prepare a root tip squash so that chromosomes can be seen.

   [3 marks]

   (b)

   Calculate the mitotic index for each root tip and use your answers to suggest the effect of the chemical on the roots.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A strawberry grower produces new plants from the runners of one parent plant. Each runner grows out from the parent, forms roots and develops into a new plant. The cells at the shoot tip of each new plant divide rapidly as it grows.

   (a)

   Explain how mitosis allows the grower to produce many new plants and how it contributes to their growth.

   [6 marks]

   (b)

   Describe the events of mitosis in a dividing cell at a shoot tip, from prophase to cytokinesis.

   [6 marks]

   Total for question 4: 12 marks

End of questions