AQA A-level Biology paper 1

large molecules often contain carbon. why? - they can readily form bonds with other carbon atoms. this forms a 'backbone'. other atoms can then attach. describe benedicts test for reducing sugars - add equal volumes of the sugar sample and benedicts reagent. heat the mixture in a water bath for 5 minutes. brick red precipitate will form. what is a reducing sugar? - a sugar that can reduce (give electrons to) another chemical. describe the benedicts test for non reducing sugars - with food sample, add an equal volume of dilute hydrochloric acid in a test tube. place test tube in water bath for 5 mins. add sodium hydrogencarbonate solution. heat resulting solution with an equal volume of benedicts. solution for 5 minutes. turns orange/brown. what does dilute hydrochloric acid do in the benedicts test for non reducing sugars? - it hydrolyses any disaccharide into monosaccharides, thus also forming reducing sugars. describe the structure of starch - chains of alpha glucose some chains are branched= amylopetcin some chains are coiled= amylose what purpose does the structure of amylose serve? - makes the molecule compact so it is stored more easily. what purpose does the structure of amylopectin serve? - more surface area for enzymes to work on, thus glucose molecules can be released at a much quicker rate. how is the structure of starch suited to its function? - 1. starch is insolube so it doesnt affect water potential 2. it is large enough that it doesnt diffuse out of cells 3. compact enough so that a lot of it can be stored in a small space 4. branched= each end can simultaneously be acted on by enzymes, so glucose is quickly released how is the structure of glycogen suited to its function? - 1. insoluble, so no effect on water potential of cell 2. insoluble, so doesnt diffuse out of cells 3. compact, a lot of it can be stored in a small space 4. very highly branched= each end can simultaneously be acted on by enzymes, so glucose is quickly released why do animals need highly branched glycogen? - because animals metabolic rate is faster than plants and so needs glucose to be released quicker. describe the structure of cellulose - made up of straight chains of beta glucose the chains are parallel to each other, so H bonds form cross-linkages all the H bonds together strengthens the cellulose forms microfibrils draw alpha and beta glucose - how does the structure of triglycerides relate to their properties? - 1. triglycerides have a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms, so its a good source of energy. 2. low mass to energy ratio, so theyre good energy storage molecules. 3. large and non-polar, therefore insoluble, therefore don't affect osmosis. 4. high ratio of hydrogen to oxygen atoms, so can release water when oxidised, hence provide a source of water what are the roles of lipids? - 1. source of energy 2. waterproofing 3. insulation 4. protection how does the structure of phospholipids relate to their properties? - 1. polar, therefore will position itself to form a bilayer 2. the structure allows them to form glycolipids by combining with carbohydrates within the cell-surface membrane. these are important in cell recognition. draw the structure of an amino acid - draw how a dipeptide forms - what is meant by 'primary sequence' of a protein - The unique sequence of amino acids that make up a protein or polypeptide chain what is meant by 'secondary sequence' of a protein - The way in which the primary structure of a polypeptide chain folds e.g. alpha helix or beta pleated sheets. shape is held by H bonds.