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GK For Competitive Exams in Biology-Transportation in Plants

INTRODUCTION
Plants take water and minerals from the soil through the roots and transport it to the leaves. The leaves prepare food for the plant, using water and carbon-dioxide during photosynthesis.
This process of photosynthesis prepares food for the plant which is necessary for energy to the cells. The cells use this energy to carry out vital activities of life. Therefore, food must be made available to each and every cell.
Thus, a proper system of transportation is required for the transportation of food, water and minerals. This system of transportation includes:
• Roots
• Leaves
• Xylem
• Phloem
Transport of Water and Minerals
Function of Roots
• Plants absorb water and minerals by the roots.
• The roots have root hair.
• The root hair is in the contact with the water present between the soil particles.
• The root hair increases the surface area of the root for absorption of water and mineral dissolved in the water or soil.
Vascular Tissue
• Plants have pipe-like vessels to transport water and nutrients from the soil.
• The vessels are made of special cells, forming vascular tissue.
• The vascular tissue for the transport of water and nutrients in the plant is called xylem.
• The xylem forms a continuous network of channels that connect roots to the leaves through the stem and branches and thus transport water to the entire plant.
• Leave synthesis the food which has to be transported to all the parts of the plant. This is done by phloem.
Transport of water
• In xylem tissue, vessels and tracheids of the roots stem and leaves are interconnected to form a continuous system of water-conducting channels reaching all the parts of the plant.
• At roots, cells in contact of soil actively take up ions. This creates a difference in the concentration of these ions between the root and soil. Water, therefore, moves into the root from the soil to eliminate the difference.
• This means there is steady movement of water into root xylem, creating a column of water that is steadily pushed upwards.
• However, this pressure by itself is unlikely to be enough to move water over the heights that we commonly see in plants. Plants use another strategy to move water in the xylem upwards to the highest points of the plant body.
Transpiration and its Benefits
• When the plant has an adequate supply of water, the water which is lost through the stomata is replaced by water from the xylem vessels in the leaf.
• That is, evaporation of water molecule from the cells of a leaf creates a suction which pulls water from the xylem cells of roots.
• The loss of water in the form of vapour from the aerial parts of the plant is known as transpiration.
• Transpiration helps in the absorption and upward movement of water and minerals dissolved in it from roots to the leaves.
• It also helps in transport of water is more important at night. During the day when the stomata are open, the transpiration pull becomes the major driving force in the movement of water in the xylem.
Transport of Food & other Substances
• The method of transportation of products of metabolic processes, particularly photosynthesis, from leaves, where they are formed, to other parts of the plant is called translocation.
• It occurs in phloem of vascular bundle.
• Besides, the phloem transports amino acids and other substances. These substances are especially delivered to the storage organs of roots, fruits and seeds and to growing organs.
• The translocation of food and other substances takes place in the sieve tubes with the help of adjacent companion cells both in upward and downward directions.
• The transportation in phloem requires energy.
• Materials like sucrose are transferred into phloem tissue using energy from ATP. This increases the osmotic pressure of the tissue causing water to move into it. This pressure moves the material in the phloem to tissues which have less pressure. This allows the phloem to move material according to the plant’s needs.
• For example, sugar in root or stem tissue would be transported to the buds which need energy to grow.
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