Absorption of water - wikipedia Absorption of water hide This article has multiple issues. Please help improve it or discuss these issues on the talk page. ( Learn how and when to remove these template messages ) This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. Please help to improve this article by introducing more precise citations. ( November 2011 ) This article is written like a personal reflection or opinion essay that states a Wikipedia editor 's personal feelings about a topic. Please help improve it by rewriting it in an encyclopedic style. ( November 2011 ) The roots fix the plant in the soil giving it support but the most important and life supporting function of the roots is to absorb ( A ) water and ( B ) mineral nutrients from the soil, and conduct them into the stem for supply to the leaves, flowers, fruits, etc... A. NEED OF WATER Besides being a constituent of Protoplasm, water is needed inside the plant body for 4 purposes : Photosynthesis, Transpiration, Transportation, Mechanical stiffness. 1. photosynthesis : water is used up in the Green Leaves as a raw material in the synthesis of glucose. 2. Transpiration : a large quantity of water is passed out as water vapour during transpiration, for cooling in hot weather, for producing a suction force, etc 3 transportation : transportation of substances in water solution from the root upwards into the shoot ( mineral salts ) or from leaves to other parts ( sugar etc ). 4 Mechanical stiffness : water provides turgidity ( fully distended condition ) which is necessary for the stiffness of plant tissues. B. NEED OF MINERAL NUTRIENTS mineral nutrients required by the plant are absorbed from the soil by the roots only. some of these nutrients are observed as salts ( nitrates, phosphates, sulphates, etc... ) and some are simply as ions ( potassium, calcium, magnesium, chlorine, etc... ). These elements are required as constituents of cell and cell organelles as well as in the synthesis of a variety of compounds or enzymes within the cell. CHARACTERISTICS OF ROOTS FOR ABSORBING WATER * * The ability of the roots to draw water from the soil is dependent on three characteristics : ( i ) a huge surface area provided by the rootlets and root hairs, ( ii ) root hairs containing the solution ( cell Sap ) at a concentration higher than that of surrounding soil water and ( iii ) Root hairs have thin walls 1. SURFACE AREA OF ROOTS IS ENORMOUS. it is a common experience that even a small Garden plants such as balsam when generally uprooted from the soil shows a thick bunch of rootlets ( branch roots ). when carefully examined, each rootlets would show hundred of root hairs. If all root hairs of this plant where to be laid end to end, they would cover a length of many kilometres. A botanist H.J. Dittmer ( 1937 ) worked out that a 4 month - old rye plant had an aggregate root length of about 600 km. The number of root hairs in it exceeded 14 billions and their estimated total length would have even exceed 10,000 km. Thus, alltogether, the root of any plant provides a huge surface area to facilitate the absorption of water. 2. ROOT - HAIRS CONTAIN CELL SAP, OF A HIGHER CONCENTRATION THAN THAT OF THE SURROUNDING WATER. Root hairs are the extensions of the outer ( epidermal cells ) of the roots. They also contain large vacuoles filled with a sort of solution called cell Sap. Some salts are dissolved in it and the cell sap, therefore, usually have a concentration higher than that of the surrounding water. This characteristics is an important requirement to draw in the outside water, i.e. for the occurrence of osmosis. 3. ROOT HAIR HAVE THIN WALLS. Like all plant cells, root - hairs also have two Outer layer - a cell wall and a cell membrane. The cell wall is thin and permeable. It allows the movement of water molecules and dissolved substances freely in and out of the cell. The cell membrane is very thin and semi - permeable which means that it allows water molecules to pass through, but not the larger molecules of the dissolved salts. The secret of the absorption of water from the soil by roots lies mainly in this characteristics. Contents 1 Active absorption 1.1 Active osmotic water absorption 1.2 Active non-osmotic water absorption 2 Passive absorption 3 See also 4 References Active absorption Active absorption refers to the absorption of water by roots with the help of ATP, generated by the root respiration : as the root cells actively take part in the process, it is called active absorption. According to Renner, active absorption takes place in low transpiring and well - watered plants, and 4 % of total water absorption is carried out in this process. The active absorption is carried out by two theories ; active osmotic water absorption and Active non-osmotic water absorption. In this process energy is required. Active osmotic water absorption This theory was given by Pari ( 1910 ) and Priestley ( 1921 ). According to this theory, the root cells behave as an ideal osmotic pressure system through which water moves up from the soil solution to the root xylem along an increasing gradient of D.P.D. ( suction pressure, which is the real force for water absorption ). If solute concentration is high and water potential is low in the root cells, water can enter from soil to root cells through endosmosis. Mineral nutrients are absorbed actively by the root cells due to utilisation of adenosine triphosphate ( ATP ). As a result, the concentration of ions ( osmotica ) in the xylem vessels is more in comparison to the soil water. A concentration gradient is established between the root and the soil water. Hence, the solute potential of xylem water is more in comparison to that of soil and correspondingly water potential is low than the soil water. If stated, water potential is comparatively positive in the soil water. This gradient of water potential causes endosmosis. The endosmosis of water continues till the water potential both in the root and soil becomes equal. It is the absorption of minerals that utilise metabolic energy, but not water absorption. Hence, absorption of water is indirectly an active process in a plant 's life. Active transport is in an opposite direction to that of diffusion. Active non-osmotic water absorption This theory was given by Thimann ( 1951 ) and Kramer ( 1959 ). According to the theory, sometimes water is absorbed against a concentration gradient. This requires expenditure of metabolic energy released from respiration of root cells. There is no direct evidence, but some scientists suggest involvement of energy from respiration. In conclusion, it is said that, the evidences supporting active absorption of water are themselves poor. Passive absorption This mechanism is carried out without utilisation of metabolic energy. Here, only the roots act as an organ of absorption or passage. Hence, sometimes it is called water absorption ' through roots ', rather ' by ' roots. It occurs in rapidly transpiring plants during the daytime, because of the opening of stomata and the atmospheric conditions. The force for absorption of water is created at the leaf end i.e. the transpiration pull. The main cause behind this transpiration pull, water is lifted up in the plant axis like a bucket of water is lifted by a person from a well. Transpiration pull is responsible for dragging water at the leaf end, the pull or force is transmitted down to the root through column of water in the xylem elements. The continuity of the water column remains intact due to the cohesion between the molecules and it act as a rope. Roots simply act as a passive organ of absorption. As transpiration proceeds, water absorption occurs simultaneously to compensate the water loss from the leaf end. Most volume of water entering plants is by means of passive absorption. Passive transport is no different from diffusion, it requires no input of energy : there is free movement of molecules from their higher concentration to their lower concentration. The water will enter the plant via the root cells that can be found in the roots where mainly passive absorption occurs. Also, with the absorption of water, minerals and nutrients are also absorbed. See also Atkins Renner Root Thimann References Jump up ^ Arya, R.L., Arya, R, Arya, S., Kumar, J. ( 2015 ). Fundamentals Of Agriculture ( Icar - Net, Jrf, Srf, Csir - Net, Upsc & Ifs ). Scientific Publishers. p. 162. CS1 maint : Multiple names : authors list ( link ) Jump up ^ P.K. Gupta ( 2007 ). Genetics Classical To Modern. Rastogi Publications. p. 4019. ISBN 9788171338962. http://www.tutorvista.com/content/biology/biology-iv/plant-water-relations/absorption-water-by-plants.php http://www.springerlink.com/content/qw62632354v4nm77/ https://www.jstor.org/stable/4353618 https://web.archive.org/web/20110114111737/http://www.wiziq.com/tutorial/70692-Biology-XI-11-Transport-in-plants-4-Mechanism-of-Water-Absorption Retrieved from `` https://en.wikipedia.org/w/index.php?title=Absorption_of_water&oldid=833319975 '' Categories : Plant physiology Hydrology Hidden categories : CS1 maint : Multiple names : authors list Articles lacking in - text citations from November 2011 All articles lacking in - text citations Wikipedia articles needing style editing from November 2011 All articles needing style editing Articles with multiple maintenance issues Talk Contents About Wikipedia Add links This page was last edited on 30 March 2018, at 21 : 00. 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Question: active absorption of water from the soil by the root is mainly affected by
Answer: ATP; SURFACE AREA OF ROOTS