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Learn0610Papers 1, 3 · CorePlant nutritionLeaf structure and mineral ions
Plant nutrition · Subtopic 2 of 2

Leaf Structure and Mineral Ions

Leaves are adapted for photosynthesis: broad and thin (large surface area, short diffusion distance), with a waxy cuticle, a transparent upper epidermis, a palisade mesophyll layer packed with chloroplasts, a spongy mesophyll with air spaces for gas exchange, stomata (opened and closed by guard cells) and vascular bundles (xylem brings water, phloem removes sugars). Plants also need nitrate ions to make amino acids (deficiency: stunted growth, yellow older leaves) and magnesium ions to make chlorophyll (deficiency: yellowing between veins).

Cambridge 5090 Paper 1Cambridge 5090 Paper 2Cambridge 0610 Papers 2, 4Cambridge 0610 Papers 1, 3Edexcel 4BI1 Paper 1BEdexcel 4BI1 Paper 2B≈ 30 minRevision 1 · updated 2026-10-30
Section 1 of 14

Learning objectives

  • Identify the tissues in a leaf.
  • Explain how a leaf is adapted for photosynthesis.
  • State why plants need nitrate and magnesium ions and describe deficiency symptoms.
Pause and think

Why are most leaves thin and flat rather than thick and round?

Section 2 of 14

Core idea

Start hereA solar panel that breathes

A leaf is a solar panel, a gas exchange surface and a plumbing system in a sheet thinner than a credit card.

The big idea

Leaf tissues are arranged to capture light, let gases in and out, and bring water in while removing sugar. Mineral ions supply the nitrogen and magnesium it can't get from air.

1. Leaf layers

Leaf cross-section, top to bottom

Each layer has a job.

Worked exampleLinking structure and function

Explain two features that help CO₂ reach palisade cells.

Goal
Two adaptations.
Strategy
Think about the diffusion path.
  1. stomata\text{stomata}
    Openings let CO₂ diffuse in.
  2. air spaces\text{air spaces}
    CO₂ diffuses quickly through gas to every mesophyll cell.
AnswerStomata and air spaces in the spongy layer.
✓ CheckThin leaf keeps distances short too ✓.

2. Mineral ions

  • Nitrate: for amino acids and proteins; deficiency → stunted growth, yellow older leaves.
  • Magnesium: for chlorophyll; deficiency → yellowing between veins.
Pause and think

Why do shade plants often have bigger, darker leaves?

Summary

  • Palisade: light. Spongy + stomata: gases.
  • Xylem in, phloem out.
  • Nitrate and magnesium.
Key words
Stoma
Pore in the leaf surface for gas exchange.
Guard cells
Cells that open and close a stoma.
Chlorosis
Yellowing of leaves due to lack of chlorophyll.
HistorySachs and starch. In 1862 Julius Sachs showed that starch appeared in chloroplasts only after exposure to light, linking chloroplasts directly to photosynthesis.
Fun factA million doors. A single sunflower leaf can have over a million stomata, mostly on its underside.
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