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WIunoD, , Movement up, 1.3.2 Waler, , a, , Plant, , move it into the, absorb water from the soil, and, plants, at, looked, how, We, to try and understand how this water i ., tissues. We now have, vascular, HydaHiedu, plant. Is the water movement active, ar, uh mawnuno, transported to various parts of the, eawy, be moved up a stem against, Nghtax, Since the water has to, still, passive?, it, ais, the energy for this?, gravity, what provides, unnnjud, foss H d dnop, Sutoli em, Root Pressure W, 11.3.2., , Root unUkL, , Alborlinasjud, , 1, , are actively transported into the vascular, As various ions from the soil, and increases, ocu wal, auum ,tdoby tissues of the roots, water follows (its potential gradient), HNHal ond tulir Pcum, the pressure inside the xylem. This positive pressure is called rot, , +ve, , C, , x pland, , pressure,, , LmaauHId by Mamo mit, , soft-stemmed plant and on a day, when there is plenty of atmospherie, , mágitsde low, dloey, , toot, Rmavd, CCTFCTAoN a, C8JECT2ON, t "e dhu, tu oce, Ret usuu g h t, Rady banirikunq plavt ast J, das nat dauule ., , un n o s i t n, , Max, , gudud, is -2aim. ui eh, , COn, , eai, , uhko 20m ., , pushing upwater to small heights, , in the stem. How can we see that root pressure exists? Choose a small, , dawalor sun ans, , -Roetawua e, , and can be responsible for, , near, , the base with, , a, , sharp, , blade, , horizontally, O1SLre,, early in the morning. You will soon see drops of solution ooze out ofthe, Cut t h e s t e m, , cut stem; this comes out due to the positive root pressure. If you fixa, rubber tube to the cut stem as a sleeve you can aciually collect and, measure the rate of exudation and also determine the composition of the"s0, exudates. Effects of root pressure is also observable at, night and early dso, morning when evaporationis low, and excess water collects in the formod a, , around special openings of veins, the tip of grass blades., droplets, and leaves of many herbaceous parts. Such water loss in its liquid phase r, near, , is knowm, , as, , guttation., , Root pressure can, at best,, , process of water, , only provide a modest push in the overau, transport. They obviously do not play a major rote, , water movement up tall trees., , The greatest contribution of root pressu, , may be to re-establish the continuous chains of water molecules in u, , xylem, , which often break under the, enormous tensions erca by, transpiration. Root pressure does not account for the majority, ol we, , transport; most plants meet their need by, transpirafory pul, Jouce )puil, 11.3.2.2 Cobseng, Transpiration, Wat obsenb ed, , 5 n, , hu, , Hnuh noo, Paysive), , Ine, , Despite the absence, of water, , heflow, , of aheart or a circulatory system in planral, , upward through the xylem in plants can achieve fairy, , s

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OGY, Stomata, water status of the plant, canopy structure etc., , The transpiration driven ascent of xylem sap depends mainlh., , mainly on thene, , following physical properties of water:, , Cohesion - mutual attraction between water molecules, Adhesion, as, , -, , attraction of water molecules to, , the surface of, , tracheary elements)., , Surface Tension, the, , liquicdphase, , polar surfaces, , water molecules are, attracted to each, more than to water in the, , (such, , -, , gas phase., , other in

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TRANSPORT IN, , NTS, , PLAN, , 189, Transpiratio, , 11.4.1 T r a, , and, , more, , Photosyntiesis, , {han one purpose; it, a, transpiration pull for absorption and, upplieswater forphotosynthesis, iion, , h, as, aas, , aCoTIpromise, , ral1spit, , Creates, , ,su, transports, , minerals, , surfaces,, , caf sur, coolsleaf, , from the soil to all, parts of the, sonetimes 10, , plant, to 15 degrees, by, evaporative., , cooling, , shape and siructure of the, , nmaintains, ns the, the, , Curgid, A, , ively, , transport of plants, , photosynthesising, , plants by keeping cells, , plant, insatiable need for water., esis limitedby available, which, water, h, canbe swiftly depleted, of, iration. The humidity, rainforests is, to, has, , PhotosyrnNaesisiis, , an, , transpin, , 1largely tue this vast, tranater hrom root to leaf tb, atmospherë, and, of, eolution the C, photosynthetic system is back to the soil., , y, by, , probably one of the, strategies formaximisi the availability of, CO,, while, minimising water, ants are twice as cient as C,, loss. C,, plants, in, terms, of fixing carbon, enaking sugar). However, a C plant loses only, half as, much water as a, , plant for the same amount of CO.fixed., , 11.5 UPTAKE AND TRANSPORT, Plants obtain their, , carbon, , or, , MINERAL NUTRIENTS, , and most of their, , atmosphere. However,, , oxygen from, , their remaining nutritional, obtained from minerals and water for, , CO, in, requirements, , hydrogen in the soil., , 11.5.1 Uptake, Unlike water,, , of Mineral, , C, , the, are, , lons, , all minerals cannot be passively absorbed by the roots., , wo factors account, , for this: (i) minerals are, , present in thesoil as charged, , particles (ions) which cannot move across cell membranes and (i) the, , ncentrationof mineralsin the soilis usuallylowerthan the concentration, inerals in the root. Therefore, most minerals must enter the root by, , active, abso, abso, rption, into t h e cytoplasm of epidermal cells. This needs energy, the form, responsiblefor.the, of ATP. The active uptake of ions is partly, the, for, uptake of water by, Lential gradient in roots, and therefore, le, n, , mosis. Some ions also move into-the epidermal cells passively., , ons are, , and active, , transport., absorbedd from the soil by both passive, cells actively, cells, actively pump ions, , pecific proteins i the membranes of root hair, lTom the:, epidermal cells., the cytoplasms of the, tO, endoddOdermal cells, have many transport proteins, , embedded, , membrane,, , pump, cells, the, , ke all, , thelr plasma, in their, b u t not, , others, , the, Some solutes, where a plant, Tranbrane; they let so, controlpoints, Where a, cells, endodermal, reach the xylem) yote, athuatdijusts, us tshe the, solutes that, theproteins of, S, of, abiktyto, quantity_and types, afsulerinhas, sulerinhas theabiMtyAa, l, layer, r9ot endodetmis hecausp ofthe, only, cross, , are, , iransport ions, , one drectioh, , u

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BioLoov, 11.5.2 Translocation of, Mineral lons, After the ions have reached, xylem through active, , t cemAnum P, , Modatliam, , Root, , or, passive uptake., combination of the two, their further, the, transport, up, stem to all Dartor a, the plant is through the, transpiration, , N tnd" =acuat pat=souce, undugou= dunk, , wntan, , adamg, , nd" vice vuka, unlead, , Ph, maumby awal tiANgar, , nokganmuc annt, , stream., The chief sinks for the, mineral, elements, are the, growing regions of th, plant, such as the apical and lateral meristems., young leaves, developine, lowers. fruits and seeds, and the, storage, ions gecursat, finga, by thesetells., , omuno acd, , Stothgos e a) Sahubie, , vewbaacosets, Ps, , NK, , PNS, K, , Activé ufake, , Mineral ions are, , frequently remobilised, particularly from older, ng parts. Older dying leaves export much of theirmineral ., , FHoumane ( tAuAi), auxose S aansma, , Ranos« ( 3) nen ud, , organs.)Unlyadingof, the fne vein endings thpough, difusiof and, , to younger leaves., are, , removed, , to, , Similarly, before leaf fall in decidous plants,, minerals, other parts. Elements most readily mobilised, are, , phosphorus, sulphur, nítrogen and potassium. Some elements, that are, structural components like, are not, calcium, remobilised., An analysis of the, xylem exudates shows that though some of the, nitrogen travels as inorganic ions, much of it is, carried in the organic, , form as amino acids and related compounds. Similarly. small, amounts, of P andS are carried as, In addition, small, organic, compounds,, amount, of exchange of materials does, take place between xylem and phloem, Hence, it is not that wecan clearly, make a distinction and say categorically, that xylem transports, only inorganic nutrients while phloem transports, only organic materials, as was traditionally believed., i.6, , PHLOEM TRANSPORT: FLOW FROM SOURCE TOSINK, , Food, primarilyi sucrose.is transported by the vascular ti_sue phloem, , from a source to a sink. Usually the source is understood to be that, , part of the plant which synthesises the food, i.e., the leaf, and sink, the, wd, vsu, , part that needs or stores the food. But, the source and sink may be, reversed depending on the, season, or the plant's needs. Sugar stor, in roots may be mobilised to, become a source of food in the early sprs, when the buds of trees, act a s, for, need, , sink; they, , development of the photosynthetic apparatus., , /, , energy, , growth a, , Since the source-s, , relationship is variable, thie direction of movement in the phloem, be, , upwards, , that of the, , or, , with, , downwards,, , xylem, , i.e., bi-directional. This contrasts, where the movement is always unidirectional,, , upwards. Hence, unlike one-way flow of water in transpiration. food, in, , phloem, , sap, , as, , there is, , a source, , the sugar., , can, , be, , transported, , of sugar and, , any required directior D, sink able to use, store or I, , in, , long, , remove, , a, , mones, , Phloem sap is m inly water and sucrose, but other sugars, no, and amino acids are also, through loen, , transported ortranslocated, , p

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I1.6., , 191, , MUNCM, , 1, , The Pressure iow o r Mass 1 o w tlypoihesis Mneh), The accepted mechanism used for the translocauonol, sugars from source, to sink is called the, (see Figure, pressure, flow, hypothesis., 11.101, As, glucose is prepared at the source (by photosynth, thesis), it, is, converted to, ucrose (a dissacharide). The Sugar is then moved in, the form of, the, irnto, companion cells and then into the living phloem sieve sucrose, tube cells, by active transport. This,process of, loading at the source produees a, hypertonic condition in the phloem. water in the adjacent, xylem moves, into the phlo, loem by osmosi_s. As, osmotic pressure, , A, , o, , obe, , d, , S, , a, , (mud), , phetosKa, , enune, , builds,up the phloem, sink osmotic, pressure, , Stath, , will move to areas of lower, pressure. At the, must be reduced. Again active transport, is necessary to, move the, the, sucrose, of, and, ut, phloem sap, into the cells which, will, use, it, eaD, , lldose, , the sugar, into energy, starch, or, As sugars are removed, the, cellulose., 0smotic pressure decreases and water moves out of the, phloem., To summarise, the movement of, sugars in the phloem begins at the, SOurce, where sugars are loaded, (actively, Loading of the phloem sets up a water transported) into a sieve tube. Sew, potential gradient that facilitates oadr, the mass movement in the phloem., anverting, , -, , Phloem tissue is composed of sieve tube cells,, which form long columns, with holes in their end walls called sieve, , -unlsn du, -TY, , swell, , Sugars leave sieve tubes;, , by osmosis, , Tip of stem-, , Sugar solution flows, , Sugars enter sieve tubes;, , to regions of low, , water follows by osmosis, , turgor pressure, , =High, , turgor, pressuree, , Phloem, , orl, , - e a os mes), , PT, , plates. Cytoplasmic strands pass, through the holes in the sieve plates, so, forming continuous filaments. A_ loadimg, hydrostatic pressure in the phloem sieve, tube increases,, pressure flow, begins, and the sap moves through the, phloem., at the sink,, Meanwhile,, incoming sugars areactively transported out of the, phloem and removed, water follows, , -, , emdo osmesis, , leave sieve tube, for metabolism and, storage: water follows, , Sugars, , ,by osmosis, , 8, Root, 8urel1.10 Diagrammatic presentation of mechanism of translocation, , as, , unloa ding, , actu

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BOLoGY, as complex carbohydrates. The loss of solute produces a, potential in the phloem, and water passes out,, experiment, called girdling, w a s used to, , retuming eventuallyhighto watateE, A simple, t, through which food is transported. On the trunk ofaidentify, tree a the Se, , toylem, , up to a depth of the phloem layer, can be carefully removed,, In +hbark, of downward movement of food the, portion of the bark above hSne, the stem becomes swollen after a few weeks., the ring on, This, simple, experimen, simple, shows that phloem is the tissue, for, , responsible, , that, , transport takes place in one direction,, experiment can be performed by you easily., , exn0, translocation offneny, i.e.. towards, the rodd, roots.Th, , SUMMARY, Plants obtain, , a, , variety, , of, , surroundings especially frominorganic, water and, from environment into the, , elements, , plant as well as, , (ions) and salts from their, movement of these, nutrients, from one, , sojl. The, , plant cell to another plant cell, essentially involves movement across a, cell, membrane can be through, membrane., across cell, diffusion, facilitated transport or Transport, and minerals absorbed, active, transport. Water, by roots are transported by, and the organic material, xylem, synthesised in the leaves is transported, to other, parts of plant through, Passive transport (diffusion, osmo_is) and, phloem., of nutrient, active, are, the, transport, two, transport across cell membranes in, modes, living organisms. In passive, transport, nutrients move across the, membrane by diffusion,, energy as it is always dowm the, without any use of, This diffusion, concentration, and, gradiernt, hence, of substances depends on their, entropy driven., solvents. Osmosis is the, size, solubility in water, or, special type of diffusion of water, organic, membrane which depends, across, a, on, pressure gradient and, semi-permeable, active transport,, concentration gradient. In, energy in the form of ATP, a, is, utilised to pump, concentration, molecules against, of water which gradient across membranes. Water, in, is, the, potential, the, helps, movemernt of water. It, energ, and pressure, is determined by potential, The behaviour of, potential., solute potential, the cells, solution. If the, on, depends, the, of the cell is, The, surrounding, of water by solution, absorptionsurrounding, it gets, seeds and, hypertonic,, drywood takes place by a plasmolysed., diffusion called imbibition., special type oi, In higher, there is a vascular, plants,, for translocation., system, xylem and, Water, and food cannot, responsible, plant by diffusion alone. minerals, be movedphloem,, are, within, They, the, body of a, therefore, transported a, movement of substance in bulk from, by mass flow, , differences between the two, Water absorbed by rootpoints., hairs, , pathways,, , i.e.,, , system, point to another as a, result of pressure, , moves, deeper, apoplast and symplast. Various, , transported upto, , model, , one, , is the most, , a, , small, , height in stems by, acceptable to explain the, , into, , the root by two, distince, ions, and water from, soil can be, , root, , pressure., , Transpiration pul, transport of water., Transpiration 15

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193, , TRANSPORT IN PLANTS, , the loss of water in the form of vapours from the, , plant parts through stormata., , Temperature, light, humidity, wind speed and number of stomata affect the rate, , oftranspiration. Excess water is also removed through tips of leaves of plants by, guttation., , Phloem is responsible for transport of food (primarily) sucrose from the source, to the sink. The translocation in phloem is bi-directional: the source-sink, , relationship is variable. The translocation in phloem is explained by the pressureflow hypothesis.