Shoot System

• The shoot system is the part of the plant that grows above the ground.
• It consists of the stem, leaves, flowers, and seeds.

Functions of Stems

1. To support the aerial parts of the plant.
2. To transport materials (water,minerals, nutrients) between the leaves and roots.
3. To store food (e.g., potatoes).
4. Photosynthesis: some stems, especially in monocots, are green and can carry out photosynthesis (e.g., grass stems).
5. Growth: Stems in dicots are woody and grow both taller and wider over time.

• New xylem produced yearly forms wood.
• As the stem thickens, the original epidermis bursts and is replaced by bark, a new layer of dermal tissue.

6. Gas exchange: stems have lenticels, which are small openings on the stem for gas exchange.

Lenticels:

Facilitate gas exchange:

• Oxygen in.
• Carbon dioxide and water vapour out.

Stomata:

Found primarily in leaves, stomata allow:

• Carbon dioxide in.
• Oxygen out. (More oxygen is released than absorbed.)

Transverse Sections of Stems

• In dicots, the vascular bundles are arranged in a ring (xylem always towards the inside).
• In monocots, the vascular bundles are scattered at random.
• Ground tissue surrounds the vascular bundles.

Longitudinal Section of a Dicot Stem

Leaves

• Leaves are attached to stems at a node.
• The stalk of the leaf is called the petiole.
• Some leaves do not have a petiole. They are joined directly to the stem. These leaves are said to be sessile (recessive trait).

Functions of Leaves

7. Photosynthesis.
8. Gas exchange through stomata.
9. Transpiration: allows water to pass out of the leaf as vapour.
10. Food storage e.g. spinach, cabbage.

Venation

• The pattern of veins on a leaf is called venation.
• Veins contain the vascular tissue.
• There are two types of venation on leaves:

1. Parallel venation: Veins run parallel to one another. Found in monocots e.g. grasses.
2. Net (reticulate venation)
3. Veins form a branching network. Found in dicots e.g. rose.

Internal Structure of a Leaf