12 4 Stages of cell division in plant tissue can be observed using a light microscope. The image shows the result of a root tip squash. A (Source: AL1323910 – Jose Luis Calvo / Shutterstock / PAL) (a) (i) Which stage of cell division is shown by cell A? (1) A anaphase B interphase C metaphase D prophase (ii) The cells shown in the image are dividing by (1) A meiosis to enable sexual reproduction B meiosis to enable growth C mitosis to enable sexual reproduction D mitosis to enable growth Turn over 13 (iii) Describe how a slide can be prepared from a root tip sample to produce this image. 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(iv) The mitotic index gives the percentage of cells in a sample undergoing mitosis. Calculate the mitotic index for the 30 cells in this image. (2) ..............................................................% 14 (b) Two cultures of cells were used to investigate the cell cycle. The cells in culture A have a functioning gene called P21. The cells in culture B have no functioning P21 gene. Both cultures were treated with gamma radiation that can cause damage to DNA. They were then sampled at intervals of 12 hours and the mitotic index calculated. The results are shown in the graph below. 0 12 24 36 48 60 72 84 96 6 5 4 3 2 1 0 Time after radiation / hours Mitotic index (%) Key Culture A Culture B Deduce the effect of the P21 gene on the cell cycle when cells are treated with gamma radiation. 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(Total for Question 4 = 11 marks) Turn over 15 BLANK PAGE