Pearson International A Level Biology Core Practical 8: Determine the tensile strength of plant fibres

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

Load comparable plant fibres to failure and relate breaking force to fibre dimensions or treatment.

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 plant fibres, clamp stands, masses or force sensor, ruler or calipers, protective screen and tray. 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. Select fibres of comparable source and measure gauge length and diameter where possible.
2. Clamp without damaging the test section and add load gradually in equal increments.
3. Record the breaking force and note the failure location; reject only trials with a stated procedural fault.
4. Repeat across fibres or treatments and compare means with spread.

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: fibre type, treatment or measured cross-sectional area.
• Dependent variable: breaking force or tensile stress.
• Important controls: gauge length, loading rate, moisture, clamping method and fibre source.