AQA A Level Biology - Paper 3 (synoptic) A+ GRADED

AQA A Level Biology - Paper 3 (synoptic) A+ GRADED What are the useful properties of water and why ? - ANS 1) Water is a metabolite - in many metabolic reactions including condensation and hydrolysis 2) Water is a solvent - medium in which enzyme catalysed reactions take place (metabolic reactions ) and readily dissolves substances like inorganic ions ( as water is dipolar so totally surrounds the ions) , excretory products (urea/ammonia) , respiratory gases and small hydrophilic molecules ( amino acids , etc) 3) Water has a high latent heat of vaporisation (lots of energy required to break hydrogen bonds between water molecules so a lot of energy is used up when water evaporates ) so helps with temperature control as evaporation of sweat cools humans down 4) Water has a high specific heat capacity ( to separate the many hydrogen bonds requires a lot of energy) so acts as a buffer and resists temperature changes to maintain a constant internal body temperature 5) Water has large cohesive forces ( as hydrogen bonds stick together) so allows transportation of substances( water travelling in columns in xylem) and means water has a high surface tension when it comes into contact with air ( allowing pond skaters to walk on its surface) Why is water dipolar ? - ANS As water is made up of two hydrogen atoms and one oxygen atom , the hydrogen atoms have a slightly positive pole and the oxygen atom has a slightly negative pole making water dipolar. Hydrogen bonds - ANS Slightly negatively charged oxygen atom is attracted to the slightly positively charged hydrogen atom of other water molecules. The attraction between opposite charges is called hydrogen bonding, which are weak bonds but strong in large numbers. This makes water a major component in cells Hydrolysis - ANS Breaks a bond between two molecules by the addition of a molecule of water Condensation - ANS Joins two molecules together with the formation of a bond by the removal of a molecule of water Polymer - ANS A molecule ( carbohydrate, nucleotide or protein) made up of many monomers ( small repeating units) joined together by condensation reactions and broken down my hydrolysis Monosaccharides - ANS Are the monomers from which larger carbohydrates are made and contain the elements C H and O. They are sweet and soluble and there are three types : fructose , glucose and galactose. Hexose sugars (glucose) have the formula C6H12O6 Glucose is the product of photosynthesis and a major substrate of re