6.1 Plant nutrition – photosynthesis

Explain how the internal structure of a leaf is adapted for photosynthesis.

The leaf is the primary site of photosynthesis in most plants. Its internal structure is highly specialized to maximize light absorption and carbon dioxide uptake, while also facilitating the transport of water and products. Here's a breakdown of the key adaptations:

External Features

• Leaf Shape: The broad, flat shape maximizes surface area for light absorption.
• Leaf Arrangement: Overlapping leaf arrangement minimizes shading of lower leaves.
• Cuticle: A waxy cuticle on the leaf surface reduces water loss through transpiration.
• Stomata: Pores on the leaf surface allow for gas exchange (CO2 in, O2 out).

Internal Structure

The internal structure of a leaf is organized into distinct layers, each with specific functions:

1. Epidermis

The outer layer of the leaf, composed of tightly packed cells. It is transparent to allow light to pass through to the mesophyll.

2. Palisade Mesophyll

Located directly below the upper epidermis, this layer consists of tightly packed, elongated cells rich in chloroplasts. This arrangement maximizes light absorption.

3. Spongy Mesophyll

Located below the palisade mesophyll, this layer has irregularly shaped cells with air spaces between them. These air spaces facilitate gas exchange (CO2 and O2) within the leaf.

4. Vascular Bundles (Veins)

These contain xylem and phloem. Xylem transports water and minerals from the roots to the leaf. Phloem transports sugars (produced during photosynthesis) from the leaf to other parts of the plant.

Layer	Description	Function
Epidermis	Outer layer of transparent cells.	Allows light to pass through to the mesophyll.
Palisade Mesophyll	Tightly packed, elongated cells with many chloroplasts.	Maximizes light absorption for photosynthesis.
Spongy Mesophyll	Irregularly shaped cells with air spaces.	Facilitates gas exchange (CO2 and O2).
Vascular Bundles (Veins)	Contain xylem and phloem.	Transport water, minerals, and sugars throughout the leaf.

Figure: Suggested diagram: A cross-section of a leaf showing the epidermis, palisade mesophyll, spongy mesophyll, and vascular bundles.

The arrangement of these layers ensures efficient light capture and gas exchange, making the leaf a highly effective site for photosynthesis.