AQA A-level Biology paper 1: Questions with Merged Detailed Answers 2024/2025

Large molecules often contain carbon. why? - Ansthey can readily form bonds with other carbon atoms. this forms a 'backbone'. other atoms can then attach. describe benedicts test for reducing sugars - Ansadd 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? - Ansa sugar that can reduce (give electrons to) another chemical. describe the benedicts test for non-reducing sugars - Answith 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 hydrogen carbonate 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? - Ansit hydrolyses any disaccharide into monosaccharides, thus also forming reducing sugars. describe the structure of starch - Anschains of alpha glucose some chains are branched= amylopectin some chains are coiled= amylose what purpose does the structure of amylose serve? - Ansmakes the molecule compact so it is stored more easily. what purpose does the structure of amylopectin serve? - Ansmore 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? - Ans1. starch is insoluble so it doesn’t affect water potential 2. it is large enough that it doesn’t 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? - Ans1. insoluble, so no effect on water potential of cell 2. insoluble, so doesn’t 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? - Ansbecause animals’ metabolic rate is faster than plants and so needs glucose to be released quicker. describe the structure of cellulose - Ansmade 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 strengthen the cellulose forms microfibrils draw alpha and beta glucose - Ans how does the structure of triglycerides relate to their properties? - Ans1. 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 they’re 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? - Ans1. source of energy 2. waterproofing 3. insulation 4. protection how does the structure of phospholipids relate to their properties? - Ans1. 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.