Form 4 Biology Exam Papers 2023-2024 | Somaliland

External Structure of Leaf:

The external structure of a leaf consists of the below structures:

Figure: External Structure of a Leaf

Petiole:
Petiole is also known as leaf stalk
Petiole is the thin stalk that attaches the leaf to the main stem or branch

Lamina: 
Lamina is also known as leaf blade
It is the large broad green surface of the leaf
It gives a large surface for light absorption

Midrib:
Midrib is also known as main vein of the leaf
It is the large central thick vein of the leaf that runs through the leaf blade from its base to its apex.

Leaf margin:
Leaf margin is also known as leaf edges.
Leaf margins are thin which reduce the distance of diffusion of gases between the atmosphere and innermost leaf cells.

Leaf apex: 
Leaf apex is also known as leaf tip.
It is the terminal part of the leaf

Veins:
Leaf veins branch from the midrib of the leaf
Leaf veins contain vascular tissue of the leaf (xylem and phloem)

The main functions of the leaf veins

 

Figure: External Structure of a Leaf