AQA A-Level Biology Paper 1 2021, Exams of Advanced Education

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AQA A-Level Biology Paper 1 2021 1.1 Describe the induced fit model of enzyme action and how an enzyme acts as a catalyst. - - The substrate binds to the active site and forms an ES complex. - The active site changes shape slightly so it's complimentary to the substrate. - This reduces the activation energy. 1.2 Tick one box to show which are the substrate the scientists must add to the reaction mixture is to produce ATP. - - Adenosine diphosphate. 1.3 Suggest and explain a procedure the scientist could have used to stop each reaction. - - The nature of the enzyme by putting it in ice. 1.4 Explain the change in ATP concentration with increasing inorganic phosphate concentration - - With increasing phosphate concentration more ES complex is form. - And at 40 mol dm3, all active sites are occupied. 2.1 Explain the advantage for large animals of having a specialised system that facilitates oxygen uptake. - - Large organisms have a smaller surface area to volume ratio. - This means they overcome a long diffusion pathway. 2.2 Suggest how the environmental conditions have resulted in adaptations of systems using model A rather than model B. - - Water is more dense than air. - So it supports the gills. 2.3 A student studies figure 3 and concluded that the fish gas exchange system is more efficient than the human gas exchange system. Use figure 3 to justify this conclusion. - - The difference of oxygen concentration between the artery and vein is larger in the fish than the human. - So the fish remove a greater amount of oxygen that they intake. 2.4 Explain how the countercurrents principle allows sufficient oxygen uptake in the fish gas exchange system. - - Blood and water continuously flow in opposite directions. - So the concentration gradient is maintained along the length of the lamellae. 3.1 Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation. - - TRNA brings the specific amino acid to the ribosome. - The anticodon on the tRNA binds to the codon on the mRNA. - The amino acids join to form a peptide bond using ATP. 3.2 Use information in table to to suggest why this amino acid replacement changes the properties of crystallin. - - The hydrogen bonds form instead of the ionic bonds. - And it changes the tertiary structure of the crystallin. 3.3 MRNA codon for the non-mutant triplets. mutated mRNA codon. Mutated DNA triplet. - - AGG - GGG - CCC 4.1 Suggest two ways the student could improve the quality of his scientific drawing of the blood vessels in this dissection. - - Add labels. - Don't use shading. 4.2 Describe one feature that allows you to identify the blood vessels. Blood vessel X Blood vessel Y Feature - - Artery - Vein - They have different wall thicknesses. 8.4 Use this information on table 6 to show how each population is best adapted for its natural environment when compared with other population. - ROOT LENGTH - POP 1 grew longer roots in warm temp. - POP 2 grew longer roots in cool temp. STANDARD DEVIATION - Standard deviation doesn't overlap so the difference in mean isn't likely to be due to chance. FATTY ACIDS - POP 1 is better adapted to warm weather because it has more SATURATED fatty acids so more every is available = more growth. - POP 2 is better adapted to cool weather because it has more UNSATURATED fatty acids so there's more lipase activity = more growth. 8.5 Explain why they are both given this name - Helianthus annuus. - - Because they are from the same species. 9.3 Give the letter and name of the molecule supported and explain why the results do not support other molecules. - - Model: Q - Name: Semi-conservative DNA replication. - Explanation for first UNSUPPORTED model: P. Only has one peak is shown in generation 1. - Explanation for second UNSUPPORTED model: R. During generation 3, there should be an overlapping peak. 10.1 Describe the structure of DNA. - - Polymer of nucleotides. - Formed from deoxyribose sugar, a phosphate group and nitrogenous base. - The nucleotides are joined by phophodiester bonds. - Double helix strands are held together by hydrogen bonds. - Between Adenine + Thymine and Cytosine + Guanine. 10.2 Name and describe five ways substances can move across the cell surface membrane into a cell. - - DIFFUSION of small molecules down a conc gradient. - FACILITATED DIFFUSION of molecules down a conc gradient using protein carriers. - OSMOSIS of water molecules down a water potential gradient. - ACTIVE TRANSPORT of molecules AGAINST a conc gradient via protein carriers using ATP. - CO-TRANSPORT of two different substances using carrier proteins. 10.3 Contrast the structure of the two cells visible in the electron micrographs shown in figure 14. - - Cell A is bigger than cell B. - Cell A has LARGER ribosomes. - Cell A has a nuclei whereas cell B had free floating DNA. - Cell A had mitochondria, cell B doesn't. - Cell B has a capsule, cell A doesn't.