Pearson International A Level Biology Core Practical 2: Investigate vitamin C content in food and drink

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

Use the reducing action of vitamin C against a standardised indicator response to compare or estimate concentration.

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 DCPIP or another specified indicator, vitamin C standards, food extracts, pipettes or burette, test tubes and filtration equipment. 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 or obtain a known vitamin C standard and clarify cloudy food samples by filtration.
2. Place a fixed indicator volume in a tube and add standard dropwise with consistent mixing to a defined endpoint.
3. Repeat to obtain concordant volumes, then test each unknown with the same endpoint rule.
4. Use inverse volume or a calibration relationship only when the method and concentration range justify it.

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: vitamin C concentration or food sample.
• Dependent variable: volume required to reach the defined indicator endpoint.