Plants require water, wilted leaves recover when water is conducted upward in leaves. Leaves need water and carbon dioxide for photosynthesis to occur, food produced in leaves has to be transported to other parts of plant like stem, roots flowers and fruits. All the procedures of transport in plants are performed through conducting tissues. Movement of water and minerals within and out of cells of plants through conducting tissue is known as transport system. Transport systems in plants and animals refer to movement of materials from different parts of organisms where they are made or attained to parts where they are utilized, stored or removed from body.
Requirement for Transport System in Plants and Animals:
Transport system is essential in plants and animals as every cell of organism requires obtaining all necessary materials for metabolism like nutrients, oxygen, and water. It is also essential to remove and dispose metabolic waste like carbon dioxide, water and urea. In plants, transport is essential to move mineral salts and water from roots to stems and leaves. Transport is also needed to move hormones in plants and animals from where they are made to area of need. Glucose from leaves and storage organs are some of substance being frequently transported in plants.
Mechanisms for Movement of Molecules:
Molecules move in and out of cell through cell membrane that forms boundary of every cell. Cell membrane is selectively permeable to substances that mean that it allows entry and exit of certain molecules only. Movement of molecules occurs by osmosis, diffusion, and active transport.
Molecules move out from the region of higher concentration to region of lower concentration. For instance, in respiration, oxygen-laden air in lungs being at higher concentration moves in blood capillaries containing lower concentration of oxygen in them. This type of movement of particles or molecules from region of the higher concentration to region of the lower concentration is known as diffusion.
Osmosis is movement of water molecules from the region containing more water molecules to region having less water molecules when divided by semi-permeable membrane. Semi-permeable membrane means the membrane that permits some molecules (like water molecules) to go through it but not some other larger molecules. No energy is spent in diffusion or osmosis.
In active transport, molecules have to move (against concentration gradient) that is from the region of the lower concentration to the region of the higher concentration. Energy is needed in active transport.
Transport of Materials in Plants:
Transport of Water:
Transport system in plants happens in xylem and phloem known as vascular bundles. Roots of plants take up water and minerals from soil. Once within roots, materials are transported upward to stems, leaves, flowers, seeds and fruits. Tracheids and vessels that are non-living cells of xylem transport water selected by root hairs from soil to leaves. Upward movement of water and minerals termed ascent of sap is against gravity and is because of transpiration pull. Transpiration is process in which loads of water evaporates (as water vapour) from pores on surface of leaf known as stomata. This evaporation develops vacuum and pulls up water through xylem.
Transport of Food Material:
Sugars and other food molecules synthesized in leaves are transported to other parts of plant by phloem. Sieve tubes are living cells of phloem that transport food. Transport of food material from leaves to other parts of plant is known as translocation. Food may be accumulated in fruits, stem or roots.
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