Pearson International A Level Biology Core Practical 6: Prepare and stain a root tip squash to observe mitosis

This core practical is part of Pearson's practical-learning programme. The method below is one defensible implementation, not a confidential instruction sheet. Centres may adapt equipment while preserving the scientific purpose, controls, measurements and safety requirements.

Aim and scientific principle

Prepare or observe a thin specimen, obtain a focused image and record biological detail with scale and proportion.

Begin by translating the title into a testable question. Identify what is deliberately changed, what is measured directly, what is calculated and what must remain controlled. Predict a relationship only after naming the mechanism. A prediction without a reason is weak; a reason without measurable variables cannot guide a practical design.

Apparatus and setup

Use light microscope, slides, coverslips, forceps, mounted needle, suitable stain, ruler or eyepiece graticule and stage micrometer. Select every measuring instrument by range and resolution, not by name alone. Draw a labelled scientific setup that shows the working geometry and exactly where readings are taken. Include a control or blank when it distinguishes the target effect from drift, contamination or background response.

Before collecting results, check zero readings, calibration, leaks, alignment or sterility as relevant. Record the instrument resolution beside the first raw-data table. If a digital device displays more digits than its underlying accuracy supports, do not treat every digit as equally certain.

Method

1. Prepare a thin, flat specimen or select a suitable prepared section and add stain if required.
2. Lower the coverslip at an angle to reduce bubbles and remove excess liquid.
3. Focus at low power first, centre the region, then move to higher power without using coarse focus near the slide.
4. Calibrate the eyepiece scale when measuring, and produce a clear line drawing with title and scale.

Plan the analysis before starting. This reveals whether an additional measurement is needed for a derived quantity and prevents a completed experiment from lacking a mass, length, concentration, background or calibration value. A method should be detailed enough for another trained student to reproduce, while avoiding decorative steps that do not affect validity.

Variables and controls

• Independent variable: cell type, tissue region or treatment when a comparison is required.
• Dependent variable: cell dimensions, mitotic stage count or observed structural features.