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B3.2B3. Plant Nutrition and Transport

Leaf structure — Combined Science 0653 - Biology Revision Notes & Topical Questions

10 min read 25 parts Lesson 3 of 11 1 quiz

📚 Combined Science 0653 - Biology Hub / Topical Revision
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Lesson summary

B3.2 Leaf structure — COMBINED SCIENCE notes: Identify the structures in the leaf of a dicotyledonous plant and state the function of each.Cuticle — the waxy layer on the upper surface.Epidermis — the upper epidermis and the lower epidermis.Mesophyll — the palisade mesophyll and …

  • Stomata and guard cells
  • Vascular bundle
  • Chloroplasts
  • Air spaces
  • Stoma (plural stomata)
  • Spongy mesophyll

Part 1 of 8Structures to identify

Structures to identify
Cuticle
  • Cuticle the waxy layer on the upper surface.
Epidermis
  • Epidermis the upper epidermis and the lower epidermis.
Mesophyll
  • Mesophyll the palisade mesophyll and the spongy mesophyll, with air spaces.
Stomata and guard cells
  • Stomata and guard cells pores and the cells that control them.
Vascular bundle
  • Vascular bundle xylem and phloem.
Chloroplasts
  • Chloroplasts in the mesophyll cells.

Part 2 of 8Functions of the layers

StructureDescriptionFunction
Wax cuticleWaterproof layer on top of the leafReduces water loss by evaporation
Upper epidermisThin and transparentLets light pass to the palisade mesophyll
Palisade mesophyllColumn-shaped cells packed with chloroplastsAbsorbs as much light as possible for photosynthesis
Spongy mesophyllLarge air spaces between cellsGives a large surface for gas exchange
Lower epidermisContains most of the stomataAllows gas exchange and reduces water loss
Vascular bundleXylem and phloemTransports substances to and from the leaf

Part 3 of 8Palisade mesophyll

Position
  • Position a layer just under the upper epidermis.
Shape
  • Shape long, narrow cells packed tightly together.
Chloroplasts
  • Chloroplasts they contain many chloroplasts, which absorb light.

Part 4 of 8Spongy mesophyll

Spongy mesophyll
Air spaces
  • Air spaces large spaces between the rounded cells.
Function
  • Function carbon dioxide diffuses through the air spaces to the palisade cells and oxygen diffuses out.

Part 5 of 8Vascular bundles

Xylem
  • Xylem carries water and dissolved mineral ions up to the mesophyll cells.
Phloem
  • Phloem carries sucrose and amino acids away from the leaf.
Position
  • Position in the leaf the xylem is on the inside and the phloem is on the outside.

Part 6 of 8Stomata and guard cells

Stoma (plural stomata)
  • Stoma (plural stomata) a small pore that allows gas exchange between the leaf and the air.
Guard cells
  • Guard cells two cells around each stoma that change shape to open or close it.
Number
  • Number in most plants stomata are more numerous on the lower epidermis.

Part 7 of 8Pathway of carbon dioxide

1
Carbon dioxide diffuses from the atmosphere through the stomata.
2
It passes into the air spaces around the spongy mesophyll cells.
3
It diffuses into the mesophyll cells.
4
It reaches the chloroplasts.

Part 8 of 8More from the specification

1Balanced Photosynthesis Chemical Equation
  • Photosynthesis is an endothermic photochemical reaction summarized by: 6CO2 + 6H2O → C6H12O6 + 6O2, requiring light absorption by chlorophyll molecules.
2Investigating Leaf Starch Accumulation
  • De-starching a potted plant in darkness, exposing part of a leaf to light while shielding the rest,
    • and testing with iodine reveals blue-black starch only where chlorophyll absorbed radiant energy.
3Chloroplast Distribution Across Leaf Tissues
  • Palisade mesophyll cells packed with abundant chloroplasts are positioned directly beneath transparent epidermal cells to capture maximum photon energy for glucose synthesis.
4Indicator
  • Substance that changes colour in acids and alkalis.
5Light intensity
  • The amount of light.
6Limiting factor
  • A factor in such short supply that it restricts the rate of a process.
7Chlorophyll
  • Green pigment that absorbs energy from sunlight.
8Temperature
  • Average energy of the particles in an object.
9Glucose
  • Sugar that is the fuel for respiration.
10Starch
  • The storage carbohydrate in plants, which turns iodine blue-black.
11Carbohydrate
  • Nutrient, such as starch and sugar, that gives energy.
12Concentration
  • Amount of solute dissolved in a volume of solution.

Key terms

TermMeaning
CuticleA waterproof layer of wax on the leaf surface.
EpidermisThe thin outer layer of cells of a leaf.
Palisade mesophyllColumn-shaped cells with many chloroplasts that carry out most photosynthesis.
Spongy mesophyllLoosely packed cells with air spaces for gas exchange.
StomaA pore in the leaf surface for gas exchange.
Guard cellA cell that opens and closes a stoma.
Vascular bundleA group of xylem and phloem.

Avoid these mistakes

1
Saying the palisade layer is at the bottom — it is below the upper epidermis.
2
Saying the upper epidermis has chloroplasts — it is transparent so light reaches the palisade cells.
3
Confusing xylem and phloem — xylem carries water and phloem carries sucrose and amino acids.
4
Saying the cuticle is part of the cell — it is a waxy layer on the surface.

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