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Water Flow in Plant Tissue.

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Water Flow in Plant Tissue. Introduction and Background. Water Potential ? is the difference in intramolecular pressure exerted in a given specimen with reference to the intermolecular pressure exerted between molecules of pure free water at atmospheric pressure and the same temperature. The plant cell vacuole may be considered as a homogenous phase, separated by the tonoplast, cytoplasm and plasma membrane from the surrounding fluid. These may be considered as a single complex membrane, which is permeable only to water, that s for the purposes of this experiment. The cellulose wall which surrounds the cell is regarded as being completely permeable but of considerable strength and elasticity. Any pressure exerted by the cytoplasm on the vacuole is ignored in this experiment but is about 200 Kpa. The main pressure is exerted by the wall. In solutions of high water potential or in pure water the vacuole takes in water and expands. As a result the cytoplasm is pressed against the cell wall until the wall prevents any further expansion. Plasmolysed cell A plant cell can therefore come into equilibrium with pure water. At this point the cell has the same waster potential, as pure water i.e. ...read more.


1. A standard solution of sucrose is prepared using the formulae weight of sucrose as C11H22O11. 2. Dilutions are obtained so as to obtain a range of concentrations shown in the table below. 3. Sample of potato are freshly cut into rectangular pieces and measured for length, breath and width . As a working guide the aim was to use a length of five centimetres and a cross section of 1.4cm in other words a regular chip. A micrometer screw gauge was thought to be inappropriate here in view of the overall accuracy required in the experiment, a normal ruler was used measurements to the nearest 1mm. While working on other aspects of the experiment freshly cut chips are stored in distilled water to prevent aerial oxidation. 4. Two sample chips are placed in a constant volume of sucrose solution (10ml). 5. Thus two replicates are used for each sucrose concentration. 6. The samples are stored for 24 hours. The potato discs are removed dried between sheets of filter paper lightly and re-measured for their linear dimension. 7. A table of results will be drawn up to m record volumes before and after the experiment. ...read more.


Although the main driving force is often the transpiration rate driven by the sun. Seed germination may be slowed or prevented for example by a water deficit.. The seed surface contact is a significant factor. The seed coat is likely to be permeable to most common osmotica. Natural soil osmotica such as sodium chloride show some relationship with the nature of the habitat. Halophytes for example will germinate in relatively high sodium chloride concentrations that are inhibiting to glycophytes for example. Some desert plants are sensitive to rain. The Californian Filago californica will not germinate in moist cells, but any rainfall up to 20cm increases germination. Mass flow of solutes to the root surface may be controlled especially if elements not supplied by diffusion. For example Hoth and Norrish found the silicon content of Triticum vulgare (lemmas and glumes) to be strongly correlated with the total transported during growth. Appendix Table of Osmotic Potential in KPa of sucrose versus molarity mol dm -3 Molarity mol dm -3 Osmotic Potential Kpa 0.05 -130 0.10 -260 0.115 -410 0.20 -540 0.25 -680 0.30 -860 0.35 -970 0.40 -1120 0.45 -1280 0./50 -1450 0.55 -1620 0.60 -1800 0.65 -1980 0.70 -2180 0.75 -2370 0.80 -2580 0.85 -2790 0.90 -3000 0.95 -3250 1.0 -3500 ...read more.

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