AQA A-level Biology paper 1

AQA A-level Biology paper 1 Rated A large molecules often contain carbon. why? Ans- they can readily form bonds with other carbon atoms. this forms a 'backbone'. other atoms can then attach. describe benedicts test for reducing sugars Ans- 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? Ans- a sugar that can reduce (give electrons to) another chemical. describe the benedicts test for non reducing sugars Ans- 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? Ans- it hydrolyses any disaccharide into monosaccharides, thus also forming reducing sugars. describe the structure of starch Ans- chains of alpha glucose some chains are branched= amylopetcin some chains are coiled= amylose what purpose does the structure of amylose serve? Ans- makes the molecule compact so it is stored more easily. what purpose does the structure of amylopectin serve? Ans- 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? Ans- 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? Ans- 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? Ans- because animals metabolic rate is faster than plants and so needs glucose to be released quicker. describe the structure of cellulose Ans- 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 Anshow does the structure of triglycerides relate to their properties? Ans- 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? Ans- 1. source of energy 2. waterproofing 3. insulation 4. protection how does the structure of phospholipids relate to their properties? Ans- 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 Ansdraw how a dipeptide forms Answhat is meant by 'primary sequence' of a protein Ans- The unique sequence of amino acids that make up a protein or polypeptide chain what is meant by 'secondary sequence' of a protein Ans- 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. what is meant by 'tertiary sequence' of a protein Ans- This is the overall 3-D structure of the protein. The shape of the protein is held together by H bonds and ionic bonds and disulfide bridges. what is meant by 'quaternary sequence' of a protein Ans- If a protein is made up of several polypeptide chains that are linked in various ways, the way they are arranged is called the quaternary structure. describe the test for proteins Ans- add equal volumes of sample and sodium hydroxide to a test tube. add a few drops of dilute copper (II) sulfate and mix. if solution turns purple, protein is present. what are fiberous proteins made up of? Ans- made of long molecules arranged to form fibres (e.g. in keratin). Several helices may be wound around each other to form very strong fibres. what are globular proteins made up of? Ans- made of chains folded into a compact structure. One of the most important classes are the enzymes. Although these folds are less regular than in a helix, they are highly specific and a particular protein will always be folded in the same way. what kind of protein is collagen? Ans- fiberous what kind of protein is haemoglobin? Ans- globular what is haemoglobin made up of? Ans- two α polypeptide chains two β polypeptide chains an inorganic prosthetic haem group (Fe2+) what is collagen made up of? describe its structure? Ans- three polypeptide chains wound around each other each of the three chains is a coil itself Hydrogen bonds form between these coils Collagen molecules form further chains with other collagen molecules and form Covalent Cross Links with each other, which are staggered along the molecules to further increase stability. Collagen molecules wrapped around each other form Collagen Fibrils which themselves form Collagen Fibres. what are the functions of collagen? Ans- 1. Form the structure of bones 2. Makes up cartilage and connective tissue 3. Prevents blood that is being pumped at high pressure from bursting the walls of arteries 4. Is the main component of tendons, which connect skeletal muscles to bones what type of bond forms between the phosphate group and deoxyribose sugar in DNA? Ansphosphodiester bond why is DNA stable? Ans- 1. the phosphodiester backbone protects the more chemically reactive organic bases inside the doub