Water And Oceanography

The Basic Properties of Water



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"The Basic Properties of Water"
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Water is essential for the life of plants. It keeps them cool, keeps their cells rigid and helps them maintain their upright stance.

We know plants cannot eat as such, they can only take minerals and nutrients in solution through their root hairs. We also know that the transpiration stream is vital for plants to survive. We know root pressure, caused by the root hairs taking water in from the soil by osmosis and pumping it across the cortex by water deficit will push water up a plant around 30 feet and for most plants, this is enough.

We also know that leaf suction pull (the loss of water from stomatal opening in leaves) will pull water up around 30 feet, which, combined with root pressure makes a total of 60 feet but what about trees which are over 60 feet tall. How do they draw essential water up?
Well, to explain, here is some clarification.

Transpiration is important for the plant. It keeps water moving with its dissolved mineral salts that the plant needs for nutrition and it helps cool the plant. The air in the inter cellular air space behind the stoma becomes saturated with water that evaporates to the atmosphere via the stoma.
Water enters the root hairs by osmosis the special diffusion from water in a region of high concentration to one of lower concentration via a semi permeable membrane (cell wall in this case). Then, by osmosis it is passed across the cortex until it reaches the xylem vessels. It is passed across because as cells lose water, a water deficit is created in that cell, so it draws water from the next.

The guard cells lose water and if no more water comes from the next cell, they become flaccid. They become turgid when full of water because, unlike most of the other cells on the lower surface of a leaf, they possess large amounts of chloroplasts and so produce glucose which increases the concentration in the cell so more water is drawn in. Thus, in sunlight, the stoma are usually open as the cells actively photosynthesize.

To sum up water uptake by the plant: Leaf suction is created by the constant evaporation of water from the leaf cells and this will draw water up to 30ft. So, root pressure pushes water up 30ft, leaf suction draws water up to 30 ft which is usually enough. However, when a plant reaches over 60ft (as in some tall trees) another force comes into play this is cohesion which is the attraction of water molecules to each other and to the walls of the xylem vessels. This means the water column remains intact unless the column is broken. This means trees can be taller than the otherwise limiting factors would seem to allow (total 60 ft.

Plants are continually providing us with evidence of their creative use of chemical and physical properties of elements and this is just another way in which nature has adapted to use properties of water molecules.

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