Mitosis and the cell cycleEdexcel A-Level Biology A: Mind map

Exam questions on Mitosis and the cell cycle

1. A student prepares a root tip squash from garlic roots to observe the stages of mitosis. She cuts the last few millimetres from the tip of a root, warms it in hydrochloric acid, adds a stain that binds to DNA, and then squashes it under a coverslip before viewing it with a light microscope.
   State the purpose of (i) warming the root tip in hydrochloric acid and (ii) adding the stain.2 marks
2. Using a light microscope, the student examines a root tip squash and counts 200 cells. She finds 168 cells in interphase, 14 in prophase, 6 in metaphase, 4 in anaphase and 8 in telophase. The whole cell cycle in this species takes 18 hours.
   Calculate the mean time that a cell in this root tip spends in mitosis. Give your answer in hours to two significant figures.2 marks
3. A chemotherapy drug prevents spindle fibres from forming. Tumour cells exposed to the drug are found with condensed chromosomes, each made of two chromatids, scattered through the cell. The cells do not divide and many later die.
   Explain why chromosomes cannot be separated into two daughter nuclei when spindle formation is prevented.3 marks