The cell cycle and mitosisEdexcel A-Level Biology B: Mind map

Exam questions on The cell cycle and mitosis

1. A student prepared a temporary squash of onion root tip, stained it with acetic orcein and examined it with a light microscope. In one field of view she counted 200 cells. Of these, 24 were in the stages of mitosis and the rest were in interphase.
   Explain why the root tips are warmed in hydrochloric acid and then squashed under a coverslip.2 marks
2. A human skin cell in the G1 stage of interphase contains 46 chromosomes. Skin cells divide by mitosis to replace those lost from the surface of the body.
   Describe what happens to the chromosomes during anaphase.2 marks
3. Colchicine is a chemical extracted from the autumn crocus. It prevents spindle fibres from forming. When added to a culture of dividing cells, the cells stop dividing and their chromosomes remain condensed. Colchicine has been investigated as a treatment for some cancers.
   Explain why cells treated with colchicine accumulate in metaphase and cannot complete mitosis.3 marks