Internal Structure of a Leaf Lamina

Cuticle

• A waxy, waterproof and transparent layer which covers the upper epidermis and lower epidermis of a leaf
  • Transparent: allows sunlight to pass through it for photosynthesis
• Function
  • Avoids excessive loss of water through evaporation (transpiration)

Upper Epidermis

• Located on the upper surface of the leaf, and under cuticle layer
• The cells of upper epidermis do not contain chloroplast and are transparent to allow light to pass through it

Palisade Mesophyll

• Shape of palisade mesophyll cells: rectangular (columnar)
• Palisade mesophyll cells are arranged vertically and closely-packed to receive maximum light exposure
• Palisade mesophyll cells contain high density (amount) of chloroplasts to carry out photosynthesis

Spongy Mesophyll

• Shape of spongy mesophyll cells: irregular-shaped that increases the internal surface area for gaseous exchange
• Spongy mesophyll cells are loosely arranged and they have a lot of intercellular air space, to ease carbon dioxide and water absorption through the leaves to palisade mesophyll cells during photosynthesis
• Spongy mesophyll cells contain less density (amount) of chloroplast compared to palisade mesophyll cells

Vascular Bundle

(i) Xylem

• Function: transports water and mineral salts absorbed from the roots to the leaf
• Walls of xylem tissues are lignified and thickened to provide mechanical support and strength to the plant

(ii) Phloem

• Function: transports organic substances produced by photosynthesis (such as sugar) from leaves to storage organs such as roots, fruits and tubers

Lower Epidermis

• Located at the lower surface of the leaf
• Contains stomata. Each stoma is guarded by a pair of guard cells