2.2

• Water is a polar molecule due to uneven distribution of charge within the molecule, with the hydrogen atoms being more positive than the oxygen atom causing one end of the molecule to be more positive than the other.
• Water acts as a metabolite in metabolic reactions such as condensation and hydrolysis which are used in forming and breaking of chemical bonds.
• Water acts as a solvent in which many metabolic reactions occur.
• Water has a high heat specific capacity meaning that a lot of energy is required to warm it up, therefore minimising temperature fluctuations in living things and acting as a buffer.
• Water has a relatively large latent heat of vaporisation, meaning evaporation of water provides a cooling effect with little water loss.
• Strong cohesion between water molecules enables effective transport of water in tube-like transport cells as the strong cohesion supports columns of water.
• The surface tension at the water-air boundary is high due to strong cohesion between water molecules.
• Afterwards, a few drops of dilute copper (II) sulfate solution is added and gently mixed.
• In the presence of a protein, the solution turns lilac/ as an indicator of peptide bonds.
• In the absence of protein, the solution remains blue.
• The emulsion test is used to test for lipids.
• Firstly, 2ml of sample is added to 5ml of ethanol.
• Subsequently, the contents are mixed thoroughly by shaking to ensure that the lipids dissolved.
• Upon addition of 5ml of water and mixing, the solution turns cloudy indicating the presence of lipid due to the formation of an emulsion where the light is refracted as it passes from droplets of oil to droplets of water.
• Starch is tested for with the help of iodine – in the presence of starch, the colour of potassium iodide solution from yellow to black/blue.
• The maximum density of water is at 4 degrees, meaning that ice is less dense than water and floats on top of it creating an insulating layer, increasing the chance of survival of organisms in large bodies of water as it prevents them from freezing.
• Water is incompressible therefore it provides good support.
• Monomers are small units which are the components of larger molecules, examples of include monosaccharides (such as glucose), amino acids and nucleotides.
• Polymers are molecules made from monomers joined together.
• A condensation reaction is a reaction which joins monomers by chemical bonds and it involves the elimination of a water molecule.
• Hydrolysis is the opposite of condensation and it’s when water is added to break a chemical bond between two molecules.
• Carbohydrates are molecules which consist only of carbon, hydrogen and oxygen and they are long chains of sugar units called saccharides.
• There are three types of saccharides - monosaccharides, disaccharides and polysaccharides.
• Monosaccharides can join together to form disaccharides and polysaccharides by glycosidic bonds which are formed in condensation reactions.
• Glucose is a monosaccharide containing six carbon atoms in each molecule, it is the main substrate for respiration therefore it is of great importance.
• Alpha and beta glucose are the two isomers of glucose with the following structures: α-glucose and β-glucose.
• Maltose is a disaccharide formed by condensation of two glucose molecules.
• Sucrose is a disaccharide formed by condensation of glucose & fructose.
• Lactose is a disaccharide formed by condensation of glucose & galactose.
• Glycogen and starch are polysaccharides formed from many glucose units joined together and include alpha glucose.
• Glycogen is the main energy storage molecule in animals and it’s formed from many molecules of alpha glucose joined together by 1, 4 and 1, 6 glycosidic bonds.
• Starch stores energy in plants and it is a mixture of two polysaccharides called amylose and amylopectin.
• Amylose is an unbranched chain of glucose molecules joined by 1, 4 glycosidic bonds, as a result of that amylose is coiled and thus it is a very compact molecule meaning it can store a lot of energy.
• Amylopectin is branched and is made up of glucose molecules joined by 1, 4 and 1, 6 glycosidic bonds, due to the presence of many side branches it is rapidly digested by enzymes therefore energy is released quickly.
• Cellulose is a component of cells wells in plants and it’s composed of long, unbranched chains of beta glucose which are joined by glycosidic bonds.
• Microfibrils are strong threads which are made of long cellulose chains joined together by hydrogen bonds and they provide structural support in plants cells.
• Lipids are biological molecules which are only soluble in organic solvents such as alcohols.
• There are two types of lipids: saturated lipids such as those found in animal fats which don’t contain any carbon-carbon double bonds, and unsaturated lipids which can be found in plants and contain carbon-carbon double bonds.
• The greater the number of unsaturated bonds, the weaker the intermolecular bonds resulting in lower melting point, and as a result of that saturated fats which don’t contain any double bonds are solid at liquid temperature and unsaturated lipids are liquid at room temperature.
• Triglycerides are lipids made of one molecule of glycerol and three fatty acids joined by ester bonds formed in condensation reactions.