Leaf Structure

• Leaf


  Plant organ in which photosynthesis occurs
• Upper surface of leaf

  • Cuticle-waxy layer prevents evaporation and acts as a physical defence against microorganism infection
  • Upper epidermis
  • Cell wall
  • Vacuole
  • Chloroplast
  • Nucleus
  • Cytoplasm
  • Intercellular space
• Lower surface of leaf

  • Lower epidermis
  • Palisade mesophyll layer-cells with many chloroplasts
  • Spongy mesophyll layer-cells with air spaces between them and fewer chloroplasts in each cell
  • Stoma
  • Guard cell
• A mesophytic leaf is a typical unspecialised leaf - the plants have reasonable supplies of water, but not so much that they don't need to have some adaptations to reduce water loss
• Adaptations for light absorption

  • Large surface area
  • Thin transparent cuticle
• Adaptations for gas exchange

  • The spongy mesophyll cells have a large surface area for gas exchange
  • The intercellular spaces in the spongy mesophyll allow carbon dioxide to enter and oxygen to leave the photosynthesising cells, which are mainly concentrated in the palisade layer
  • Stomata that allow carbon dioxide and oxygen to enter the leaf; the guard cells can open and close the stomatal pore - in many plants stomata are open during the day and closed at night
• Cells and tissues found in a leaf

  • Epidermis
  • Cuticle
  • Palisade mesophyll
  • Spongy mesophyll
  • Intercellular space
  • Stoma
  • Guard cells
  • Mid rib & veins
• Epidermis


  Single layer of cells around the leaf: Upper and lower epidermis. Flat, no chloroplasts to allow light to pass through
• Cuticle


  Waxy layer covering the upper epidermis which reduces water loss
• Palisade mesophyll


  Layer of rectangular shaped cells found below the upper epidermis. Cells arranged side by side, no spaces-traps as much sunlight as possible. Many chloroplasts - lots of photosynthesis
• Spongy mesophyll


  Layer of round cells below palisade cells with fewer chloroplasts, less photosynthesis. Contains air spaces called intercellular spaces
• Intercellular space


  Spaces between the spongy mesophyll cells which allow diffusion of oxygen, carbon dioxide and water between inside the leaf and the air outside
• Stoma


  A small pore found between the cells of the lower epidermis
• Guard cells


  The 2 cells that surround each stoma which allow the stoma to open and close, controlling movement of gases in and out of the leaf
• Mid rib & veins


  Contain vascular bundles made up of xylem and phloem. Xylem carries water to the leaf cells from the roots. Phloem carries sucrose sugar made in the leaf cells to other parts of the plant
• Photosynthesis


  Carbon Dioxide + Water -> Glucose + Oxygen
• The oxygen made in photosynthesis is a waste product. It is either used in respiration or leaves the leaves through the stomata
• Variegated leaf