A veterinary technician made a small, sterile cut in the tail fin of young zebrafish. Fig. 1 shows two microscope views of cells at the edge of a wound. In ...
Question 1 Report
A veterinary technician made a small, sterile cut in the tail fin of young zebrafish. Fig. 1 shows two microscope views of cells at the edge of a wound. In view A, chromosomes are arranged across the middle of a cell. In view B, two groups of chromosomes are moving apart. The fish were held in clean water at 26 degrees C. Table 1 gives the number of cells in each stage seen at 10 hour intervals after the cut. New cells help replace damaged tissue, but blood clotting first prevents excessive loss of blood.
Table 1
| time after cut / h | cells in mitosis | cells not in mitosis |
|---|---|---|
| 0 | 8 | 192 |
| 10 | 31 | 169 |
| 20 | 46 | 154 |
| 30 | 19 | 181 |
(a) Name the stage of mitosis shown in view A. [2]
(b) Describe the change in the number of cells in mitosis between 0 h and 30 h. [3]
(c) Suggest why the number of dividing cells rises after the cut. [2]
(d) Use Fig. 1 to state what must happen to the chromosomes before two new cells are formed. [2]
Answer Details
(a) View A is metaphase [2]. In metaphase, chromosomes line up across the equator, or middle, of the cell. This matches the chromosomes arranged centrally in the view.
(b) The number of cells in mitosis increases from 8 at 0 h, reaches a maximum of 46 at 20 h, then decreases to 19 by 30 h [3].
(c) The cut damages fin tissue, so replacement cells are needed [1]. Mitosis produces genetically identical new cells for this repair [1].
(d) Before two new cells form, sister chromatids, the copies of each chromosome, must separate [1]. One complete set then moves to each end of the cell, so each daughter cell receives a full set [1].
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