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Cambridge IGCSE Biology · 0610

Chapter 6: Plant nutrition (Part 3)

Leaf adaptations for photosynthesis

Large surface area
To absorb as much light energy as possible.
Thin
To allow for efficient gas exchange and short diffusion distances.

Internal leaf structure

  1. Waxy cuticle: A clear, waterproof layer that reduces water loss without blocking light.
  2. Upper epidermis: Transparent to let light pass through to the mesophyll; acts as a protective barrier.
  3. Palisade mesophyll: Positioned near the top; cells contain many chloroplasts to absorb light energy efficiently.
  4. Spongy mesophyll: Contains air spaces to increase surface area for rapid diffusion of CO2, oxygen, and water vapour.
  5. Vascular bundle: The transport system containing the xylem (transports water/ions) and phloem (transports sucrose/amino acids).
  6. Lower epidermis: Contains guard cells and stomata.
    • Stomata: Pores that allow CO2 in and O2/water vapour out.
    • Guard cells: Control the opening and closing of stomata to limit water loss.
Transverse section of a dicotyledonous leaf labelling cuticle, epidermis, mesophyll layers, vascular bundle, guard cells and stomata
Diagram 1: Leaf cross-section. A transverse section of a dicotyledonous leaf showing the waxy cuticle, upper epidermis, palisade mesophyll, spongy mesophyll with air spaces, vascular bundle (xylem and phloem), lower epidermis, guard cells, and stomata.

Exam Traps

  • Do not swap xylem and phloem substances or positions in the leaf bundle.
  • Avoid saying stomata are for absorbing light — they allow gas exchange.

Mineral requirements

Plants actively take up minerals through root hair cells:

Nitrate ions
Needed for making amino acids, which are used to build proteins and enzymes; deficiency leads to poor growth and yellow leaves.
Magnesium ions
Needed for making chlorophyll; deficiency leads to a lack of chlorophyll (yellow leaves) and an inability to photosynthesise effectively.

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