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kirby1001 kirby1001
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9 years ago
.... i don't know what this is for (.-.)
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wrote...
9 years ago
wrote...
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Educator
9 years ago
1. Cohesion is the sticking together of similar molecules. Water is very cohesive. This allows water to be pulled along a pathway with relative ease.

2. Surface Tension: cohesion allows water to pull together and form droplets or form an interface between it and other surfaces. The measure of how hard it is to break this interface is its surface tension.
Water allows materials to rest upon it if the surface tension is not broken. Pollen, dust, water insects, and other biological materials are able to remain on the surface of the water because of this tension.

3. Adhesion: The sticking of one substance to another. Water is a good adhesive. It will cling on to many objects and act as a glue. Capillary Action is an example of cohesion and adhesion working together to move water up a thin tube like the xylem in plants.

4. Imbibition: The process of soaking into a hydrophilic substance. Water being taken into a sponge, into a seed, into paper towels.

5. High Specific Heat: Specific heat of a substance is the heat needed (gained or lost) to change the temperature of 1g. of a substance 1degree Celsius. This high specific heat allows water to act as a heat sink. Water will retain its temperature after absorbing large amounts of heat, and retain its temperature after losing equally large amounts of heat. The reason for this is that Hydrogen bonds must absorb heat to break. They must release heat when they form.The Ocean acts as a tremendous heat sink to moderate the earth's temperature.

6. High Heat of Vaporization: Water must absorb a certain amount of additional heat to change from a liquid into a gas. This extra heat is called heat of vaporization. In humans, this value is 576 cal/g. This results in evaporative cooling of the surface. Alcohol has a value of 237cal/g. and chloroform 59cal/g.
As one can see water removes much more heat from a surface upon evaporation than does either alcohol or chloroform.

7. Freezing and Expansion of Water: Water is most dense at 4 degrees C. At ) degrees C. it is 10% less dense. Ice floats because maximum Hydrogen bonding occurs at 0 degrees C. This protects aquatic organisms from freezing in very cold environments.

8. Versatile Solvent: Water is a major solvent in nature. Living organisms are mainly water allowing chemical reactions to occur without difficulty.
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wrote...
9 years ago
Role of water as a solvent

Water is a solvent for numerous biochemical moleculesm giving solutions and enabling:

-Transport of nutrients, e.g. glucose and amino acids in blood, and sucrose in phloem
-Removal of excretory products, e.g. ammonia, urea
-Secretion of substances, e.g. hormones, digestive juices.

Role of water in metabolic reactions

The majority of essential metabolic reactiosn take place in solution in water. Water is a raw material or a product of many metabolic reactions.

-Hydrolysis involves the addition of water (hydro) in the breakdown (lysis) of large biological molecules into their monomers/subunits, e.g. proteins into amino acids. (Water is release during condensation reactions).
-Water produced as a metabolic product of respiration is essential for organisms, especially those living in dry habitats. It is the final electron acceptor in the electron transport chain.
-Water is needed for photosynthesis as water is split in the photolysis of water, in order to replace the electrons lost from chlorophyll, and to provide protons for the NADPH.

Role of water in support

Water is not easily compressed and has an important role in support in plants and animals

-The uptake of water by plant cells creates a pressure against the rigid cell wall.
-This turgor pressure helps non-woody plants to remain upright.
-Water provides buoyancy for aquatic organisms, e.g whales.
-Water has a high specific tension and water molecules have cohesive forces holding them together, due to hydrogen bonding between water molecules.
-These properties allow aquatic insects to walk on the surface of water, and water to be pulled through xylem in plants.
-Transpiration of water from the stomata allows water to be pulled up the stem. This brings essential nutrients with it.

Role of water in temperature regulation

Water has a high specific heat capacity which means it adsorbs a lot of heat energy for its temperature rise, and loses a lot to cool. This help to:

-Reduce temperature fluctuations in organisms - especially large ones.
-Minimize increases in temperature in cells as a result of biochemical reactions.
-Reduce fluctuations in temperature in aquatic habitats.

A lot of heat is needed to turn water into vapour (it has a high latent heat of vaporisation)

-This helps some animals to maintain a constant body temperature as a high amount of heat energy is removed from the body to evaporate sweat or during planting.
-In plants evaporation of water from leaves has a cooling effect.

At 4*C water is at its maximum density and becomes less dense as it freezes.

-Water is denser as a liquid than as a solid
-Thus cold water forms ice on the upper surface, insulating the aquatic organisms below.
-Water must lose a relatively large amount of heat energy to freeze, making the formation of ice crystals in cells less likely.
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