Biology 9700 · AS & A Level · Testing for biological molecules

Testing for biological molecules — practice question

Meristematic tissue occurs in the active growth zones of plants, for instance at root tips. Fig. 2.1 shows a section through the meristematic region of an onion root tip, Allium cepa.
(main)

Table 2.1 gives the cell counts in the different stages of the cell cycle that were observed in sections of the meristematic regions of root tips of $A.\ cepa$.

(a)[3]

Complete Table 2.1 by selecting the letters A to H from Fig. 2.1 to identify one cell in each stage of the cell cycle.

(b)[2]

The total time required for meristematic cells of $A.\,cepa$ to finish one cell cycle at $25\,^{\circ}\text{C}$ is $12$ hours. From sections like the one in Fig. 2.1, the time spent in each stage of the cell cycle can be estimated. To make the estimate, first calculate the percentage of cells in that stage. Using the data in Table 2.1, calculate: • the percentage of cells in anaphase • the mean length of time in minutes for anaphase. Show your working.

(c)[1]

State one event that takes place during cytokinesis in the cell cycle of plant cells, such as those shown in Fig. 2.1.

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