Pearson International A Level Biology Core Practical 1: Estimate reducing sugar and starch concentrations using colour standards

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 calibrated colour standards to estimate food-test response, while keeping reagent volumes, heating and observation conditions consistent.

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 known glucose or starch standards, Benedict's or iodine reagent as appropriate, test tubes, pipettes, water bath, timer and colour reference. 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 labelled concentration series and one unknown using equal sample volumes.
2. Add a fixed reagent volume; use the same heating time and temperature for Benedict's tests or the same observation conditions for iodine.
3. Order standards by concentration and compare the unknown against them under constant lighting.
4. Record an interval estimate if the unknown lies between standards, and repeat independently.

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: known reducing-sugar or starch concentration.