AQA A level Biology Revision Questions & Answers with rationales 2024/2025 Grade A+

AQA A level Biology Revision Questions & Answers with rationales 2024/2025 Grade A+ 1. Describe how you would use a biochemical test to show that a solution contained a non-reducing sugar, such as sucrose. [3] - ANSWER-, first reducing sugars test; boil with dilute HCl acid then Neutralize with NaHCǑ, add benedict and heat to 95 degrees C brick red ppt forms if reducing sugar is present 2. Describe a chemical test you could carry out to show that a piece of coconut contains lipids. [3] - ANSWER- (Crush in) ethanol / alcohol; Add (to) water (Order of adding is critical for this point); Emulsion / white colour 3. Explain what is meant by a polymer. [1] - ANSWER-Molecule) made up of many identical/similar molecules/monomers/ subunits; 4. Name the reaction which occurs when starch is broken down into maltose. [1] - ANSWER-Hydrolysis 5. What is the formula for lactose? [2] - ANSWER-C12 ; H22Ō1 6. Describe how β-glucose molecule differs from a molecule of α-glucose. [1] - ANSWER-H at top right end (instead of OH) / OH at bottom (carbon 1) 7. Show two ways in which the structure of cellulose is different from the structure of starch. [2] - ANSWER-Starch 1,4 and 1,6 bonds / branching Cellulose 1,4 bonds / no 1,6 bonds / straight; starch All glucoses /monomers same way up cellulose Alternate glucoses upside down; starch Helix / coiled/compact cellulose Straight; Starch monomer Alpha glucose Cellulose monomer Beta glucose 8. Describe the structure of starch and explain how its structure is related to its function. [3] - ANSWER-Formed from α glucose; Joined by condensation/ by the removal of a water molecule/ glycosidic bonds; Between (carbons) 1 and 4 (and 1 and 6); Coiled chain; compact; (Allows) storage of large amount in a small space; Insoluble so has no effect on osmosis/water potential; Branches; (Allows) rapid breakdown/release of glucose / hydrolysis; 9. The structure of a phospholipid molecule is different from that of a triglyceride. Describe how. [2] - ANSWER-triglyceride has three fatty acids and phospholipid has two; no phosphate group present in triglyceride but present in phospholipid. 10. What is an unsaturated fatty acid? [1] - ANSWER-Some / two carbons with only one hydrogen / (double bonds) between carbon atoms / not saturated with hydrogen; 11. Describe the structure of cellulose and explain how its structure is related to its function. [3] - ANSWER-Alternate β-glucose rotated 180o, long straight chains, many hydrogen bonds join (polysaccharide) chains/molecules to each other / makes microfibrils / gives tensile strength; 12. Which elements are found in proteins? [1] - ANSWER-Carbon, hydrogen, oxygen, nitrogen (sometimes Sulphur) 13. Describe how you would use a biochemical test to show that a solution contained protein. [2] - ANSWER-Biuret / alkali + copper sulphate; Lilac/purple/mauve/violet; 14. Which bonds are found in a) Primary structure [1]b) Secondary structure [1] c) Tertiary structure [2] - ANSWER-a) Peptide b) Hydrogen (and peptide) c) Ionic, desulphated bridges, hydrophobic interactions (hydrogen and peptide) 15. Explain how a change in the primary structure of a globular protein may result in a different three-dimensional structure. [3] - ANSWER-Sequence of amino acids changes; tertiary structure changes/folds in a different way; bonds form in different places (not peptide); 16. Describe how two-way chromatography is carried out. [2] - ANSWER-Run chromatogram then turn through 90/right angle; With a different solvent; 17. Explain the advantage of using two-way chromatography to separate short polypeptides. [2] - ANSWER-Spreads spots/polypeptides out more/ make sure spot only contains one substance; 18. Explain how inhibitors affect the rate of enzyme-controlled reactions. [6] - ANSWER-Statement about two types, competitive and non-competitive; Competitive: Similar shape to substrate; Inhibitor can enter/bind with active site (of enzyme);Non-competitive: Affect/bind to enzyme other than at active site; Distorts shape of active site; Inhibitors: Prevent entry of/binding of substrate to active site; Therefore fewer/no enzyme-substrate complexes formed; 19. Describe and explain how an increase in temperature affects the rate of an enzyme-controlled reaction. [5] - ANSWER-Rate of reaction increases; Increasing temperature increases rate of movement of molecules/ kinetic energy; Collide more often/substrate enters active site more often/more enzyme-substrate complexes formed; Up to optimum; Rate of reaction decreases; High temperatures cause denaturation/loss of tertiary structure/3D structure; By breaking specified bonds (not peptide bond); Active site altered/substrate cannot bind/fit/ 20. An enzyme catalyses only one reaction. Explain why [2] - ANSWER-(Enzyme has) active site; Only substrate fits (the active site); 21. Describe the induced fit model of enzyme action. [2] - ANSWER-Active site / enzyme not complementary; Active site changes (shape) / is flexible; (Change in enzyme allows) substrate to fit / E-S complex to form; 22. Describe one way that the lock and key model is different from the induced fit model. [1] - ANSWER-Active site does not change (shape) / is fixed (shape) / is rigid / does not wrap around substrate / (already) fits the substrate / is complementary (before binding); Continues....