The internal parts of a leaf

Internal parts of a leaf

When a cross-section of a leaf is observed under a microscope, its internal structure reveals several specialized layers and tissues that perform specific functions. These include the upper epidermis, mesophyll layer, and lower epidermis. Let’s explore these in detail:

Cuticle

The cuticle is a thin, waxy, transparent layer found on the outer surfaces of both the upper and lower epidermis.

Functions:

1. Prevents water loss by reducing evaporation.
2. Protects the leaf from pathogens and mechanical damage.
3. Allows sunlight to pass through to the inner layers for photosynthesis.

Upper and lower epidermis

Upper epidermis

The upper layer of the epidermis located on the top side of the leaf.

Features:

1. Contains no chloroplasts, as its main role is protection, not photosynthesis.
2. Covered by the cuticle.

Function: Protects the leaf's internal tissues and allows light to pass through.

Lower epidermis

The lower layer of the epidermis found on the underside of the leaf.

Features:

1. Contains stomata, which are small openings for gaseous exchange.
2. Typically has more stomata than the upper epidermis.

Function:

1. Facilitates gas exchange (entry of carbon dioxide and exit of oxygen).
2. Regulates water loss through transpiration.

Stomata

Small openings in the epidermis, mostly on the lower surface of the leaf.

Features: Surrounded by guard cells that control their opening and closing.

Functions:

1. Allow carbon dioxide to enter the leaf for photosynthesis.
2. Enable the release of oxygen as a by-product of photosynthesis.
3. Facilitate water vapor loss during transpiration.

Mesophyll layer

The mesophyll is the middle layer of the leaf located between the upper and lower epidermis. It is the primary site of photosynthesis.

Components of the Mesophyll Layer:

Palisade mesophyll

1. Found just beneath the upper epidermis.
2. Made of tightly packed, elongated cells rich in chloroplasts.

Function: Main site of photosynthesis due to the high concentration of chloroplasts.

Spongy mesophyll

Found below the palisade layer and above the lower epidermis.

Composed of loosely packed cells with large air spaces.

Functions:

1. Facilitates the exchange of gases like carbon dioxide and oxygen.
2. Aids in the movement of water vapor during transpiration.

Air spaces

Found within the spongy mesophyll layer.

Function:

1. Allow gases (CO₂, O₂) to circulate freely within the leaf for photosynthesis and respiration.

Vascular tissue (veins)

Found within the mesophyll layer and composed of:

Xylem

Function: Transports water and dissolved mineral salts from the roots to the leaf for photosynthesis.

Phloem

Function: Distributes the food produced during photosynthesis (glucose) to other parts of the plant for storage and use.