Pearson International A Level Biology Core Practical 10: Investigate factors affecting photosynthesis in an aquatic plant

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

Measure oxygen production or another photosynthetic response while controlling light, temperature and carbon-dioxide availability.

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 aquatic plant, bicarbonate solution, lamp, ruler, water bath or heat shield, gas collection or oxygen sensor and timer. 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. Acclimatise a similar plant shoot in bicarbonate solution at the first light condition.
2. Measure light distance or intensity and keep temperature stable with a water bath or heat shield.
3. Collect gas volume or log oxygen concentration for a fixed interval after equilibration.
4. Repeat across at least five light values, randomise order if drift is likely and calculate mean rates.

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: light intensity or distance, as defined by the method.
• Dependent variable: oxygen volume or concentration change per unit time.