6.2Plant Nutrition

Leaf structure — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions

5 min read 5 parts Lesson 3 of 6 1 quiz

📚 Cambridge IGCSE Biology 0610 Hub / Topical Revision

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Lesson summary

Photosynthesis and leaf structure — IGCSE BIOLOGY notes: Gas exchange in leaves; Leaf structure and adaptations.Pathway of CO2 — atmosphere → stomata → air spaces around spongy mesophyll → mesophyll cells → chloroplasts, all by diffusion.Day and night — plants respire all the tim…

Hydrogencarbonate indicator
Overall adaptations
Guard cell
Palisade mesophyll
Vascular bundle
In the dark only respiration occurs: oxygen is taken in and CO2 is released

Part 1 of 3Gas exchange in leaves

1Pathway of CO₂

Pathway of CO₂ atmosphere → stomata → air spaces around spongy mesophyll → mesophyll cells → chloroplasts, all by diffusion.

2Day and night

Day and night plants respire all the time but photosynthesise only in light.
In bright light photosynthesis exceeds respiration: net uptake of CO₂ and net release of O₂.
In the dark only respiration occursoxygen is taken in and CO₂ is released.

3Hydrogencarbonate indicator

Hydrogencarbonate indicator shows CO₂ level, because CO₂ is acidic in water.

Purple — low CO₂; red — atmospheric level; yellow — high CO₂.

Tube	Conditions	Indicator	Conclusion
Leaf in light	Light	Purple	Net intake of CO₂
Leaf in dark	Dark	Yellow	Net release of CO₂ by respiration
No leaf (control)	Light	Red	Control for comparison

Part 2 of 3Leaf structure and adaptations

Leaf cross-section and adaptations for photosynthesis

Structure	Function / adaptation
Waxy cuticle	Waterproof layer that reduces water loss by evaporation; transparent so light passes through
Upper epidermis	Thin and transparent, so light reaches the palisade layer
Palisade mesophyll	Tall, tightly packed cells with many chloroplasts near the top surface, giving maximum light absorption
Spongy mesophyll	Loosely packed with large air spaces, so CO₂ and O₂ diffuse quickly; fewer chloroplasts
Lower epidermis with stomata and guard cells	Stomata allow gas exchange and can close to reduce water loss; guard cells change shape as they gain or lose water; more stomata on the lower surface reduce water loss
Vascular bundle (vein)	Xylem brings water and mineral ions; phloem carries away sucrose and amino acids; also supports the leaf

Overall adaptations of the leaf for photosynthesis.
- Large surface area absorbs more light and allows more gas exchange.
- Thin, so CO₂ has a short diffusion distance to the mesophyll cells.
- Network of veins supplies water and removes products.

Part 3 of 3More from the specification

Key terms

Term	Meaning
Stoma	A pore in the leaf epidermis, surrounded by two guard cells, that allows gas exchange.
Guard cell	One of a pair of cells that change shape to open or close a stoma.
Palisade mesophyll	A layer of tall, tightly packed cells with many chloroplasts; the main site of photosynthesis.
Spongy mesophyll	A layer of loosely packed cells with air spaces for gas diffusion.
Cuticle	A waxy waterproof layer covering the leaf that reduces water loss.
Vascular bundle	Xylem and phloem in a vein, transporting water and sucrose.

Avoid these mistakes

Plants respire only at night — they respire all the time and photosynthesise only in light.

Last updated: 24 October 2026