O-Level Biology Photosynthesis Limiting-Factor Studio

TL;DR
Photosynthesis tasks connect Section 3 plant nutrition outcomes with MMO precision and ACE explanations about limiting factors.
Practise at least one gas-collection/bubble-count investigation and one indicator-based assay, then translate the data into rate graphs with crisp commentary.

1 | Exam focus

• The syllabus requires candidates to describe how light intensity, CO₂ concentration, and temperature affect photosynthesis (SEAB 2026 syllabus, PDF).
• Paper 3 builds on this by assessing:
  • Planning: identifying the limiting factor, setting up controls, and justifying apparatus choices (e.g. data loggers, coloured filters).
  • MMO: counting bubbles consistently, measuring colour changes, recording probe readings.
  • PDO: tabulating rate data, plotting graphs, labelling axes with units.
  • ACE: explaining trends with limiting-factor theory, evaluating reliability, proposing improvements.

2 | Cabomba bubble-count core practical

1. Place a freshly cut sprig of Cabomba or Elodea upside down in a beaker filled with 0.2 % sodium hydrogencarbonate solution.
2. Position a lamp at 10 cm distance; allow 5 minutes for acclimatisation.
3. Count oxygen bubbles released in 1 minute for three consecutive minutes; take the mean.
4. Repeat with lamp distances of 20 cm, 30 cm, 40 cm. Keep room temperature constant (cite thermometer use).
5. Optional: wrap the beaker in coloured acetate sheets to compare red, blue, and green light.

Record data like this: