MSH | B6 Plant nutrition

B6.1

Photosynthesis

Success criteria: state word and balanced equations; explain chlorophyll's role; describe uses of carbohydrates and mineral ions; explain limiting factors and interpret gas-exchange indicators.

carbon dioxide + water → glucose + oxygen
light + chlorophyll
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Watch: photosynthesis

Open on YouTube if needed.

Uses of carbohydrate

Also: sucrose for phloem transport and nectar to attract pollinators.

Nitrate ions are needed to make amino acids. Magnesium ions are needed to make chlorophyll.

B6.1 practical/data skills

Limiting-factor simulator

Adjust light intensity, carbon dioxide concentration and temperature. The slowest factor limits the overall rate.

Light intensity 70%CO₂ concentration 60%Temperature 25 °C

Relative photosynthesis rate

A plateau means another factor has become limiting. Temperature rises to an optimum then falls because photosynthesis is enzyme-controlled.

Hydrogen carbonate indicator challenge

In bright light, an aquatic plant removes CO₂ faster than it releases CO₂ by respiration. What happens to CO₂ concentration?

B6.2

Leaf structure and adaptation

Click a structure in the cross-section to reveal how it supports photosynthesis.

Structure explorer

Select a structure.

Quick check

Why are palisade cells near the upper surface?

Exam practice

[2]1. State the balanced symbol equation for photosynthesis.

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

[4]2. Explain why increasing light intensity may stop increasing the rate of photosynthesis.

At first light is limiting; increased light raises rate; eventually light is no longer limiting; another factor such as CO₂ concentration or temperature limits the rate.

[4]3. Explain two adaptations of a leaf for photosynthesis.

Any two linked explanations: large surface area absorbs more light; thin leaf gives short diffusion distance; palisade cells near upper surface contain many chloroplasts; stomata allow CO₂ entry; spongy air spaces speed diffusion; xylem supplies water; phloem transports sucrose.

[3]4. A plant has yellow leaves because of mineral deficiency. Name the likely deficient ion and explain why photosynthesis decreases.

Magnesium ions; needed to make chlorophyll; less chlorophyll means less light energy absorbed and a lower rate of photosynthesis.

Sources and teacher note

Aligned to the Cambridge IGCSE Co-ordinated Sciences (Double Award) 0654 syllabus for examinations in 2025–2027. The 0973 course has the same subject content. Embedded video links were checked during creation on 14 September 2026.

Video: Cognito, “GCSE Biology – Photosynthesis”.

This independent learning resource is not endorsed by Cambridge International. Cambridge-style questions are original and are not copied from past papers.