Leaf structure — Cambridge IGCSE Biology
How the structures of a dicotyledonous leaf are adapted for photosynthesis.
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A leaf is the organ where most photosynthesis takes place, and most leaves are thin with a large surface area to absorb more light. Palisade mesophyll cells near the upper surface contain most of the chloroplasts. Air spaces in the spongy mesophyll let carbon dioxide diffuse to the cells, and stomata let gases in and out.
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Quick check questions
State two features of most leaves.
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Large surface area and thin.
Where are most chloroplasts found in a leaf?
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In the palisade mesophyll cells.
What is the function of the guard cells?
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To open and close the stomata.
Frequently asked questions
How are leaves adapted for photosynthesis?
Leaves are adapted for photosynthesis by being thin with a large surface area. The large surface area absorbs more light, and the thin shape means light reaches all the cells and carbon dioxide has only a short distance to diffuse. Palisade mesophyll cells near the upper surface contain many chloroplasts and absorb most of the light.
Why are most chloroplasts in the palisade mesophyll?
Most chloroplasts are in the palisade mesophyll because these tall, tightly packed cells lie near the upper surface, where they receive the most light. The thin, transparent upper epidermis and cuticle let light pass through to them. As a result, the palisade cells absorb most of the light, and most photosynthesis happens there.
What is the function of the spongy mesophyll?
The spongy mesophyll is made of rounded cells with air spaces between them. Carbon dioxide diffuses through these air spaces to the photosynthesising cells, and oxygen diffuses out towards the stomata. The spongy mesophyll cells also contain chloroplasts, so they carry out some photosynthesis too.
What do stomata and guard cells do in a leaf?
Stomata are pores, mostly in the lower epidermis, that let carbon dioxide diffuse into the leaf and oxygen diffuse out. Each stoma is surrounded by two guard cells that change shape to open and close it. Closing the stomata reduces water loss, and the waxy cuticle on the surface also reduces water loss by evaporation.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026