Nucleic Acids: - Water

- Water - 

Dipolar water molecule: water is made up of two atoms of hydrogen and one of oxygen. The molecule has no overall charge although oxygen has a slightly negative charge and hydrogen has a slightly positive charge.

Water and hydrogen bonding:

A positive pole of one water molecule would attract the negative pole of another water molecule, the attraction force between the opposite charges is a hydrogen bond. Each bond is weak, however together they form important forces that cause water molecules to stick together, giving water unusual properties.

Specific heat capacity:

Water molecules stick together, it takes more energy -heat- to separate them then if they did not bond to one another. Resulting in the boiling point being high (100 degrees celsius)

Without hydrogen bonding water would be a gas at temperatures on earth.

Water acts as a buffer against sudden temperatures variations - aquatic environment is a temperature stable one.

Organisms are mostly water, protects them from sudden temperature change especially in terrestrial environment.

Latent heat of vaporisation of water:

Hydrogen bonding = lots of heat energy required to evaporate 1 gram of water. - latent heat of vaporisation.

Evaporation of water in mammals is therefore a very effective means of cooling, body heat is used to evaporate the water.

Cohesion and surface tension:

Tendency of molecules sticking together = cohesion

• Hydrogen bonding = large cohesive forces, allowing it to be pulled through a tube - xylem vessel
• Water molecules meet air, tend to be pulled back into the body of water than escaping from it = surface tension.
• Water acts like a skin, strong enough to support small organisms - pond skaters

Importance of water to living organisms:

Water in metabolism -

• Used to breakdown complex molecules - hydrolysis
• Joins molecules together through the use of condensation reaction
• Chemical reactions take place in aqueous medium
• Water = major raw material in photosynthesis

Water as a solvent -

• Readily dissolves other substances - gases ie, oxygen + carbon dioxide
• Waste - ammonia + urea
• Inorganic ions + small hydrophilic molecules - amino acids, monosaccharides, + ATP
• Enzymes - reactions which takes place in a solution.

Important features of water:

• Evaporation cools and allows organisms to control their temperature.
• Not easily compressed = providing support - hydrostatic skeleton of animals// earthworm + turgor pressure in herbaceous plants
• Transparent = aquatic plants can photosynthesise // light penetrate jelly like fluid that fills the eye and reach the retina.