3.2 - Organ for Water and Mineral Salts Uptake

The roots of the plants are the most important parts in water and mineral salts absorption. The roots go deep into the centre of the earth and regions that contain water. The roots have 2 major functions which are

1. Support and strengthen the position of the plants.
2. Absorb water and mineral salts from the soil and transport them to the stems and leaves.

The Root Structure for Water and Mineral Salts Uptake

Figure 1 - The structure of the plant roots.

Root Adaptations for Water and Mineral Salts Uptake

Figure 2 - The internal structure of the plant root. Vascular cylinder consists of xylem, phloem and pericycle.

Parts, Characteristics and functions

Epidermis

• Cells are arranged closely
• Thin cell wall and water-permeable cell membrane allows diffusion of water into the roots
• Epidermal cells form root hairs by elongating laterally
• Root hair cells without cuticle enables water absorption
• Root hair cells have large vacuole to store water and mineral salts so that water can be absorbed continuously and fast

Cortex

• Found underneath epidermis layer
• Thin cell wall allows diffusion of water into the roots
• Cells are arranged loosely to allow exchange of gases efficiently
• Most of the cells are parenchyma cells

Endodermis

• This layer separates the cortex from the vascular cylinder
• Cells are arranged very close together and are only one-cell thick
• Most of the cell walls are thickened with lignin or suberin which forms Casparian strips
• Only water and mineral salts can enter the vascular cylinder

Vascular cylinder

• Consists of xylem and phloem tissues surrounded by pericycle tissues which are only one-cell thick
• Pericycle is involved in secondary growth and formation of lateral roots
• Xylem and phloem tissues are arranged in a star-shaped pattern
• Xylem tissues transport water and mineral salts
• Phloem tissues transport organic substances (sucrose) and plant hormones