2.1 - Structure of a Leaf

The leaves are the major organs of plants that are involved in the photosynthesis process. The structure of a leaf can be categorized into 2 parts.

• The external structure which consists of lamina and petiole.
• The internal structure

The word photosynthesis comes from the Greek word. 'Photo' means light and 'synthesis' means arranged together or producing.

The External Structure of a Leaf

Figure 1 - The external structure of the leaf.

The Internal Structure of a Leaf Lamina

Most the leaf lamina are arranged in a way where there will be no overlapping. This arrangement is called leaf mosaic which allows maximum sunlight for photosynthesis.

Figure 2 - Cross-section of a leaf lamina.

Structures, Characteristics and functions

Cuticle

• Covers the upper and lower epidermis of the leaf
• Waxy, waterproof and transparent
• Helps to prevent excessive loss of water through evaporation (transpiration)
• Enables penetration of sunlight (transparent)

Upper epidermis

• Located at the upper surface of the leaf/ underneath the cuticle layer
• Epidermal cells do not have chloroplasts
• Transparent to allow penetration of sunlight

Lower epidermis

• Found at the lower surface of the leaf
• Presence of stoma formed from a pair of guard cells

Palisade mesophyll

• The cells are arranged vertically and compactly to obtain maximum sunlight
• Site of photosynthesis
• Cells contain a lot of chloroplasts

Spongy mesophyll

• Irregular-shaped cells which increase the surface area for gaseous exchange
• The cells are arranged loosely with many air spaces between the cells
• The air spaces allow the diffusion of carbon dioxide dan water into the cells for photosynthesis
• The number of chloroplasts is much lesser than palisade mesophyll cells

Vascular bundle

• Consists of xylem and phloem
• Xylem transports water and mineral salts from the roots to the leaves
• The walls of the xylem are lignified and thick which provide mechanical support
• Phloem transports organic substances produced from photosynthesis from the leaves to other parts of the plants