Edexcel GCSE Combined Science CB6 Plant structures and their functions: a complete overview of photosynthesis, leaves and transport

What CB6 actually demands

Plant structures and their functions covers how plants feed themselves by photosynthesis and how they move water and food around. The examiners reward the photosynthesis equation, confident handling of limiting-factor graphs from the core practical, and a clear distinction between xylem and phloem.

This guide walks through the topic and ties together the matching dot-point page, which has its own practice questions.

Photosynthesis

Photosynthesis makes glucose using light energy and is endothermic:

The glucose is used in respiration, stored as starch, made into cellulose, or combined with nitrate to make proteins.

Limiting factors

The rate is set by limiting factors: light intensity, carbon dioxide concentration and temperature. The factor in shortest supply limits the rate, and when a rate graph levels off a different factor has become limiting. The core practical investigates light intensity using pondweed, often counting oxygen bubbles, and may use the inverse-square relationship between distance and light intensity.

Leaf structure and transport

A leaf is broad and thin with chloroplasts in the palisade layer and stomata (controlled by guard cells) for gas exchange. Plants transport substances in two tissues:

• Xylem - water and minerals, roots to leaves, one way.
• Phloem - dissolved sugars, around the plant, both ways (translocation).

Transpiration is water loss from the leaves; it pulls water up the xylem and speeds up with heat, wind, light and low humidity.

How CB6 is examined

• Equations. The word and symbol equations for photosynthesis.
• Graphs. Interpreting limiting-factor graphs from the pondweed core practical.
• Structure to function. Explaining how a leaf is adapted for photosynthesis.
• Transport. Distinguishing xylem and phloem and explaining transpiration.

Check your knowledge

A mix of recall and application questions covering CB6. Attempt them under timed conditions, then check against the solutions.

1. State the word equation for photosynthesis. (2 marks)
2. Is photosynthesis endothermic or exothermic? (1 mark)
3. Name the three limiting factors of photosynthesis. (2 marks)
4. Explain why a photosynthesis rate graph levels off. (2 marks)
5. Name the tissue that transports water in a plant. (1 mark)
6. Name the tissue that transports sugars in a plant. (1 mark)
7. Define transpiration. (2 marks)
8. State two factors that increase the rate of transpiration. (2 marks)