Shoot System (Leaving Cert Biology): Revision Notes
📚 Revision Notes
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
- To support the aerial parts of the plant.
- To transport materials (water,minerals, nutrients) between the leaves and roots.
- To store food (e.g., potatoes).
- Photosynthesis: some stems, especially in monocots, are green and can carry out photosynthesis (e.g., grass stems).
- 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.
- Gas exchange: stems have lenticels, which are small openings on the stem for gas exchange.
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A node is a part on the stem where new branches and leaves grow.
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Internodes are areas between nodes where no branches form.
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
- Photosynthesis.
- Gas exchange through stomata.
- Transpiration: allows water to pass out of the leaf as vapour.
- 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:
- Parallel venation: Veins run parallel to one another. Found in monocots e.g. grasses.
- Net (reticulate venation)
- Veins form a branching network. Found in dicots e.g. rose.
Internal Structure of a Leaf
