Explain in your own words with suitable examples.
Describe the transportation system in plants.
Transportation is a life process where substances synthesised or absorbed in one part of the body are carried to other parts of the body. The transportation system in plants moves the energy stored in leaves to different parts. It also helps in moving raw materials absorbed from the roots to various organs of the plant. However, these are entirely different pathways. The transportation system in plants consists of two different types of conducting tissues. Xylem conducts water and minerals obtained from soil (via roots) to the rest of the plant. Phloem transports food materials from the leaves to different parts of the plant body.
Transportation of water
The first step in transportation of water is absorption of water by roots of plants. As the water is absorbed by the roots from the soil and moved to the vascular system, it has to be transported to various parts of the plant. Two forces responsible for transporting the water up in a plant are root pressure and transpiration pull.
Root Pressure is the positive pressure created inside the xylem when water follows the ions transported along the concentration gradients into the vascular system. However, majority of water is transported through transpiration pull.
Transpiration pull is the pull of water as a result of tension created by transpiration is the major driving force of water movement upwards in a plants. It accounts for loss of 99% of water taken by the plant and this loss is mainly through stomata. As the water is released by leaves into the atmosphere, the water level in the epidermal layer decreases. To compensate this water loss, water is brought to the leaves through xylem. Transpiration helps in the absorption of water and minerals to all the parts of the plants.
Transportation of food
The transportation of food from the leaves to other parts of the plant occurs in the vascular tissue, phloem and this process of transporting food is known as translocation. The phloem also transports amino acids and other substances to storage organs of the plant (along with the growing organs) such as roots, fruits, and seeds. The phloem consists of companion cells, sieve tubes, phloem parenchyma, and fibres.
The translocation of food occurs in the sieve tubes with the help of companion cells.
Translocation in the phloem, unlike the xylem, is achieved by utilizing energy from ATP. For example, a food material such as sucrose is transported into the phloem tissue using ATP energy. As a result, the osmotic pressure in the tissue increases, causing the water to move into it. This pressure moves the material in the phloem to the tissues, which have less pressure. This is helpful in moving materials according to the requirements of the plant.
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