Making a temporary slide of stained cells and identifying the stages of mitosis are both on the 9700 practical list. By hand, cut the last few millimetres of a garlic root on a tile, time it in warm hydrochloric acid on the stopwatch, add a drop of toluidine blue, lower a cover slip and squash it with your thumb through filter paper. Focus at ×10 with the coarse and then the fine knob, turn to ×40, and classify at least 50 cells with the cell counter. Finish with your own table, the mitotic index, the percentage in each stage, a drawing and the evaluation. Every attempt is a different root. Allow about 40 minutes.
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A fresh tip of 2 to 5 mm, 4 to 6 minutes in the warm acid, at least a minute and a half in the stain, a cover slip and a firm squash through filter paper; then the microscope focused at ×10 with the coarse and fine knobs before the ×40 objective, which is focused with the fine knob only.
Column headings with a unit only where there is one (number of cells; percentage of cells / %), counts that are the cells you really classified, at least 50 cells from more than one field of view, and at least 85 % of them identified correctly.
Mitotic index = cells in prophase, metaphase, anaphase and telophase ÷ total cells, from your own counts, as a decimal to 2 or 3 places or a percentage to 0 or 1 place; the percentage in each stage to the same number of decimal places; and the conclusion that the share of cells in a stage reflects how long it lasts.
The high-power drawing with large, clear continuous lines, no shading, a two-line cell wall and the chromosomes placed correctly for the stage named, then label lines that touch the cell wall, the cytoplasm and a chromosome.
Acid hydrolyses the middle lamella so the cells separate, the squash makes a single layer, only the meristem at the tip divides; more fields and more root tips with a mean for a reliable index; and the hazard, precaution and level of risk for the warm acid and the stain.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.