AQA A level Biology Revision Questions.docx

Describe how you would use a biochemical test to show that a solution contained a non-reducing sugar, such as sucrose. [3] - correct answer ,first reducing sugars test; boil with dilute HCl acid then Neutralise with NaHCǑ, add benedict and heat to 95 degrees C brick red ppt forms if reducing sugar is present Describe a chemical test you could carry out to show that a piece of coconut contains lipids. [3] - correct answer (Crush in) ethanol / alcohol; Add (to) water (Order of adding is critical for this point); Emulsion / white colour Explain what is meant by a polymer. [1] - correct answer Molecule) made up of many identical/similar molecules/monomers/ subunits; Name the reaction which occurs when starch is broken down into maltose. [1] - correct answer Hydrolysis What is the formula for lactose? [2] - correct answer C12 ; H22Ō1 Describe how β-glucose molecule differs from a molecule of α-glucose. [1] - correct answer H at top right end (instead of OH) / OH at bottom (carbon 1) Show two ways in which the structure of cellulose is different from the structure of starch. [2] - correct 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 Describe the structure of starch and explain how its structure is related to its function. [3] - correct 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; The structure of a phospholipid molecule is different from that of a triglyceride. Describe how. [2] - correct answer triglyceride has three fatty acids and phospholipid has two; no phosphate group present in triglyceride but present in phospholipid. What is an unsaturated fatty acid? [1] - correct answer Some / two carbons with only one hydrogen / (double bonds) between carbon atoms / not saturated with hydrogen; Describe the structure of cellulose and explain how its structure is related to its function. [3] - correct answer Alternate β-glucose rotated 180o, long straight chains, Many hydrogen bonds join (polysaccharide) chains/molecules to each other / makes microfibrils / gives tensile strength; Which elements are found in proteins? [1] - correct answer Carbon, hydrogen, oxygen, nitrogen (sometimes sulphur) Describe how you would use a biochemical test to show that a solution contained protein. [2] - correct answer Biuret / alkali + copper sulphate; Lilac/purple/mauve/violet; Which bonds are found in a)Primary structure [1]b)Secondary structure [1] c)Tertiary structure [2] - correct answer a)Peptide b) Hydrogen (and peptide) c)Ionic, disulphide bridges, hydrophobic interactions (hydrogen and peptide) Explain how a change in the primary structure of a globular protein may result in a different three-dimensional structure. [3] - correct answer Sequence of amino acids changes; tertiary structure changes/folds in a different way; bonds form in different places (not peptide); Describe how two-way chromatography is carried out. [2] - correct answer Run chromatogram then turn through 90/right angle; With a different solvent; Explain the advantage of using two-way chromatography to separate short polypeptides. [2] - correct answer Spreads spots/polypeptides out more/ make sure spot only contains one substance; Explain how inhibitors affect the rate of enzyme-controlled reactions. [6] - correct 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; Describe and explain how an increase in temperature affects the rate of an enzyme controlled reaction. [5] - correct 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/ An enzyme catalyses only one reaction. Explain why [2] - correct answer (Enzyme has) active site; Only substrate fits (the active site); Describe the induced fit model of enzyme action. [2] - correct answer Active site / enzyme not complementary; Active site changes (shape) / is flexible; (Change in enzyme allows) substrate to fit / E-S complex to form; Describe one way that the lock and key model is different from the induced fit model. [1] - correct 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); Explain why the rate of reaction of an enzyme is low away from its optimum pH. [3] - correct answer (change in pH) leads to breaking of bonds holding tertiary structure/ changes charge on amino acids; enzyme/protein/active site loses shape/denatured; substrate will not bind with/fit active site; fewer/no ES complexes formed; A protein molecule contains 150 amino acids. What is the total number of peptide bonds in this molecule? [1] - correct answer 149 How do you calculate magnification? [1] - correct answer M= I (Image)/ A (actual size) Describe the ways in which prokaryotic cells and eukaryotic cells differ. [3] - correct answer Prokaryotic cells do not have a nucleus / have genetic material in cytoplasm; DNA in loop / ring; Not associated with proteins / do not have chromosomes /chromatin / do not divide by mitosis; Smaller ribosomes; No membrane-bound organelles; Such as mitochondria / lysosomes / endoplasmic reticulum / Golgi / chloroplasts; Prokaryotic cells may have mesosomes; Prokaryotic cells smaller; May be enclosed by capsule; What is the function of: a)Ribosome b)Smooth ER c)Golgi apparatus d) Chloroplast e)Mitochondria [5] - correct answer a)Protein synthesis b)Lipid synthesis and transport c)Processing and packaging proteins for secretion d)Photosynthesis e)Aerobic respiration to produce ATP Explain the advantages and limitations of using a transmission electron microscope [5] - correct answer Advantages: Small objects can be seen; TEM has high resolution as wavelength of electrons shorter; Limitations: Cannot look at living cells as cells must be in a vacuum; must cut section / thin specimen; Preparation may create artefact; Does not produce 3D or colored image; Why an electron microscope can be used to produce images [2] - correct answer EM gives high resolution due to short wavelength of electrons; Explain how viruses cause damage to cells. [3] - correct answer uses / breaks up / digests host nuclear / genetic material (allow references made to DNA /RNA instead of nuclear /genetic); virus DNA / genetic material inserted into hosts DNA / chromosome / genetic material; host cells amino acids are used to synthesize viral proteins; cell lysis; by enzyme (produced by expressing a virus gene); toxin production; Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells. [5] - correct answer Cell homogenisation to break open cells; 1. Accept suitable method of breaking open cells. Filter to remove (large) debris / whole cells; 2. Reject removes cell walls. Use isotonic solution to prevent damage to mitochondria / organelles; Keep cold to prevent / reduce damage by enzymes / use buffer to prevent protein / enzyme denaturation; Centrifuge (at lower speed / 1000 g) to separate nuclei / cell fragments / heavy organelles; Re-spin (supernatant / after nuclei / pellet removed) at higher speed to get mitochondria in pellet / at bottom. Name two structures present in eukaryotic cells that are not present in the cells of prokaryotes. [2] - correct answer Nucleus; mitochondria; chloroplast, Golgi, RER; SER; centrioles Describe the fluid-mosaic structure of a cell surface membrane.(5/8 marks) - correct answer Phospholipids and proteins; Phospholipid bilayer; Arrangement of phospholipid molecules 'Tails to tails';'Floating'(protein) molecules / molecules can move in membrane;Intrinsic proteins extend through bilayer; Extrinsic proteins in outer layer only;(Ref. to intrinsic and extrinsic, unqualified, gains 1 mark);Detail of channel proteins / protein shapes / glycoproteins;Presence of cholesterol between phospholipids. Describe the part played by cell surface membranes in regulating the movement of substances into and out of cells.(6/10 marks) - correct answer 1. Non-polar/lipid soluble molecules move through phospholipid layer/bilayer;2. Small molecules/water/gases move through phospholipid layer/bilayer;3. Ions/water soluble substances move through channels in proteins;4. Some proteins are gated;5. Reference to diffusion;6.Carriers identified as proteins;7. Carriers associated with facilitated diffusion;8. Carriers associated with active transport/transport with ATP/pumps;9. Different cells have different proteins;10. Correct reference to cytosis; Describe the role of the enzymes of the digestive system in the complete breakdown of starch. (6 marks) - correct answer 1. Amylase;2. (Starch) to maltose:3. Maltase;4. Maltose to glucose;5. Hydrolysis;6. (Of) glycosidic bond; Explain how the small intestine is adapted to its function in the absorption of the products of digestion. (6/9 marks) 1. - correct answer Large surface area provided by villi / microvilli;2. long / folds increase surface area / time for absorption;3. thin epithelium;4. short diffusion pathway;5. capillary network absorbs amino acids / sugars;6. lacteal for absorption of digested fats;7. Maintains a steep concentration gradient;8. mitochondria supply ATP / energy for active transport;9. carrier proteins (in membranes); Describe and explain the role of diffusion in the absorption of digested food by the ileum. (4 marks) - correct answer 1. movement along / down concentration gradient;2. monoglycerides / micelles/fatty acids move into epithelial cells;3. monoglycerides move from epithelium into blood;4. chylomicrons move into lacteals / lymph;