Structure and Function of the Leaves

• Leaves are the photosynthetic organ of the flowering plants.
• Adaptations of the leaves to photosynthesis are including;

1.   Leaves have large broad surface
2.  Leaves have thin edges
3. Leaves have branched network of veins
4. Leaves contain chlorophyll
5. Presence of  stomata on their lower surface
6. Presence of intercellular air spaces 

External Structure of a Leaf:

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

• .     Petiole:

Petiole is also known as leaf stalk

Petiole attaches the leaf to the rest of the plant.

•        Lamina

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 main central vein of the leaf which arises from the petiole

•         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 branched from the midrib of the leaf and form network structures.

Leaf veins contain both xylem and phloem.

Functions of the leaf veins:

a)    Provide support for the softer tissues of the leaf blade

b)    Supply water and minerals to the photosynthetic cells in the leaves

c)    Carry away the manufactured food to other parts of the plant

The arrangement of veins in a leaf is called the venation pattern.

Monocots and dicots differ in their patterns of venation.

Monocots have parallel venation in which the veins run in straight lines across the length of the leaf without converging.

In dicots, however, the veins of the leaf have a net-like appearance, forming a pattern known as reticulate venation. 

Figure: Comparison between dicot and monocot leaves

Figure: External structure of a leaf

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