Required Practical 2: Root-Tip Mitosis

Young growing root-tip regions contain many dividing cells. In the centre’s approved preparation, suitable treatment softens tissue and staining increases chromosome contrast. A squash spreads cells into a thin layer so individual chromosomes are less obscured by overlapping tissue.

Use the specified stain, treatment and slide-handling procedure, including controls for corrosive reagents, heating and breakable glass where relevant. Pressing a coverslip vertically helps spread tissue without dragging chromosomes across the slide. These method choices affect image interpretation, not just the appearance of the preparation.

Begin with a low-power objective to locate a suitable thin region, then increase magnification and use appropriate fine focusing. Calibrate a graticule at the objective setting if measuring dimensions. Draw observed features with clear lines, sensible proportions and labels rather than inventing organelles not visible.

Classify cells by chromosome arrangement: condensed but unaligned chromosomes suggest prophase, an equatorial group metaphase, separating groups anaphase and two reforming nuclei telophase. Interphase has no corresponding set of clearly condensed mitotic chromosomes. Count representative fields with a consistent inclusion rule rather than selecting only obvious dividing cells.

Mitotic index is cells in mitosis divided by all cells counted, reported as a proportion or percentage. State whether all mitotic stages were included. A different index can reflect a changed division rate, altered stage duration or sampling differences; it is not automatically proof of faster growth.

Inferring stage duration from the fraction of cells in a stage assumes a suitable asynchronous, steady population and representative sample. A treatment that arrests cells in one stage can increase that stage’s proportion while reducing successful division. Keep observed proportions separate from the causal interpretation.

Try each question before opening the worked response. Use precise biological terms, connect each cause to its effect, and check units and assumptions when interpreting data.