Water and its functions


Water being dipolar

Water is classed as dipolar because it is made up of oxygen and hydrogen. The oxygen has a slightly negative charge where the hydrogen has a slightly positive charge. This means it has both negative and positive poles, which makes it dipolar.

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Water and hydrogen bonding

As there are two poles in water and different poles attract, the positive pole of one water molecule will be attracted to the negative pole of another. The force between these charges is a hydrogen bond. Although each bond is fairly weak, collectively they form important forces that cause the water molecules to stick.

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Properties of water

As water molecules stick to each other, more energy required to separate them. This makes boiling point higher and without the h2 bonds, water would be a gas. So, more energy to heat a given mass of water so has a high specific heat capacity. It acts as a buffer to sudden temp changes.

Hydrogen bonds between molecules mean lots of energy needed to evaporate 1g of water- the energy is called latent heat of vapourisation. Evaporation of water such as sweat is effective as cools the body by using body heat to evaporate water.

Cohesion is where molecules stick together. From h2 bonds, makes large cohesive forces and allows water to be pulled up a tube, like a xylem vessel. Surface tension is where water meets air it is pulled back in the body rather than escaping. Water surface acts like skin - strong enough to support pond skaters.

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Importance of water to living organisms

Mammals are typically 65% water. 

It is used to break down complex molecules by hydrolysis. Produced in condensation reactions. Major material in photosynthesis and reactions occur in aqueous medium- these all equates to the importance of water in metabolism.

Water dissolves other substances like gas, wastes like ammonia and urea, inorganic ions and enzymes. This makes water a suitable solvent.

Its evaporation cools organisms down to control their temp, not easily compressed to provides support, it is transparent and so aquatic plants can photosynthesise and light rays can penetrate.

Inorganic ions occur in cytoplasm of cells like haemoglobin transports o2, phosphate ions form structural role in DNA, hydrogen ions in determining the pH of solutions.

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