TRANSPORT IN PLANTS

Transportation 

Transportation in plants is the process in which substances absorbed or synthesized in one part of the plant are moved to other parts of the plant.

Transportation of water and food in plants is carried out by a conducting system consisting of two main tissues: Xylem and Phloem. Together, they form the vascular bundle.

Xylem

This tissue forms a tubular passage to transport water and mineral salts from the roots to the aerial parts of the plants.

The xylem tissues comprises of four types of cells:

• Tracheids are dead cells that are thick-walled with lateral pores. They are elongated cells with tapered ends. They help in conduction of water in the plant and provide mechanical strength
• Vessels are tube-like structures with open ends. They are dead cells which are arranged one above the other to form a channel. They help in conduction of water and provide mechanical strength.
• Xylem Parenchyma are the only living cells of the xylem tissue. They are thick-walled and help in the storage of food and conduction of water.
• Xylem Sclerenchyma (Fibres) are dead cells, which are long, narrow with tapered ends. They are thick-walled due to lignin deposit. They provide mechanical strength to the plant.

Phloem

This tissue transports food manufactured by leaves to various parts of the plant body. It extends along the length of the plant body, in the root, stem, branches and leaves.

The phloem tissue comprises of four types of cells:

• Sieve tubes are formed of cylindrical cells that are devoid of nucleus. They are found arranged in vertical rows, placed end to end. Their end walls are perforated and are called sieve plates. Through these sieve plates, food material passes from cell to cell.
• Companion cells are living, thin-walled, elongated cells found attached to the sides of the sieve tubes and they help in the conduction of food.
• Phloem Parenchyma is formed of thin-walled parenchymatous cells. These cells store food.
• Phloem Sclerenchyma (Fibres) are dead sclerenchyma fibres formed of elongated cells. These fibres provide mechanical strength and support to the plant.

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