AQA A level Biology Revision questions and solutions

AQA A level Biology Revision questions and solutions

Describe how you would use a biochemical test to show that a solution contained a non-reducing sugar, such as sucrose
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[3] - answers,first reducing sugars test; boil with dilute HCl acid then Neutralise with NaHCǑ, add benedict and heat to 95
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degrees C brick red ppt forms if reducing sugar is present
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Describe a chemical test you could carry out to show that a piece of coconut contains lipids. [3] - answers(Crush in) ethan
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/ alcohol; Add (to) water (Order of adding is critical for this point); Emulsion / white colour
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Explain what is meant by a polymer. [1] - answersMolecule) made up of many identical/similar molecules/monomers/
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subunits;
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Name the reaction which occurs when starch is broken down into maltose. [1] - answersHydrolysis
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What is the formula for lactose? [2] - answersC12 ; H22Ō1
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Describe how β-glucose molecule differs from a molecule of α-glucose. [1] - answersH at top right end (instead of OH) / O
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at bottom (carbon 1)
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Show two ways in which the structure of cellulose is different from the structure of starch. [2] - answersStarch 1,4 and 1,6
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bonds / branching Cellulose 1,4 bonds / no 1,6 bonds / straight; starch All glucoses /monomers same way up cellulose
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Alternate glucoses upside down; starch Helix / coiled/compact cellulose Straight; Starch monomer Alpha glucose
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Cellulose monomer Beta glucose
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Describe the structure of starch and explain how its structure is related to its function. [3] - answersFormed from α glucos
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Joined by condensation/ by the removal of a water molecule/ glycosidic bonds; Between (carbons) 1 and 4 (and 1 and 6)
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Coiled chain; compact; (Allows) storage of large amount in a small space; Insoluble so has no effect on osmosis/water
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potential; Branches; (Allows) rapid breakdown/release of glucose / hydrolysis;
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The structure of a phospholipid molecule is different from that of a triglyceride. Describe how. [2] - answerstriglyceride ha
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three fatty acids and phospholipid has two; no phosphate group present in triglyceride but present in phospholipid.
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What is an unsaturated fatty acid? [1] - answersSome / two carbons with only one hydrogen / (double bonds) between
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carbon atoms / not saturated with hydrogen;
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Describe the structure of cellulose and explain how its structure is related to its function. [3] - answersAlternate β-glucos
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rotated 180o, long straight chains, Many hydrogen bonds join (polysaccharide) chains/molecules to each other / makes
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microfibrils / gives tensile strength;
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Which elements are found in proteins? [1] - answersCarbon, hydrogen, oxygen, nitrogen (sometimes sulphur)
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Describe how you would use a biochemical test to show that a solution contained protein. [2] - answersBiuret / alkali +
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copper sulphate; Lilac/purple/mauve/violet;
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Which bonds are found in a)Primary structure [1]b)Secondary structure [1] c)Tertiary structure [2] - answersa)Peptide b
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Hydrogen (and peptide) c)Ionic, disulphide bridges, hydrophobic interactions (hydrogen and peptide)
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,Explain how a change in the primary structure of a globular protein may result in a different three-dimensional structure. [
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- answersSequence of amino acids changes; tertiary structure changes/folds in a different way; bonds form in different
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places (not peptide);
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Describe how two-way chromatography is carried out. [2] - answersRun chromatogram then turn through 90/right angle
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With a different solvent;
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Explain the advantage of using two-way chromatography to separate short polypeptides. [2] - answersSpreads
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spots/polypeptides out more/ make sure spot only contains one substance;
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Explain how inhibitors affect the rate of enzyme-controlled reactions. [6] - answersStatement about two types, competit
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and non-competitive; Competitive: Similar shape to substrate;Inhibitor can enter/bind with active site (of enzyme);Non-
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competitive: Affect/bind to enzyme other than at active site; Distorts shape of active site; Inhibitors: Prevent entry ro ro ro ro ro ro ro ro ro ro ro ro ro ro ro ro




of/binding of substrate to active site; Therefore fewer/no enzyme-substrate complexes formed;
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Describe and explain how an increase in temperature affects the rate of an enzyme controlled reaction. [5] - answersRat
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of reaction increases; Increasing temperature increases rate of movement of molecules/ kinetic energy; Collide more
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often/substrate enters active site more often/more enzyme-substrate complexes formed; Up to optimum; Rate of reacti
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decreases; High temperatures cause denaturation/loss of tertiary structure/3D structure; By breaking specified bonds
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(not peptide bond); Active site altered/substrate cannot bind/fit/
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An enzyme catalyses only one reaction. Explain why [2] - answers(Enzyme has) active site; Only substrate fits (the activ
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site);
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Describe the induced fit model of enzyme action. [2] - answersActive site / enzyme not complementary; Active site
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changes (shape) / is flexible; (Change in enzyme allows) substrate to fit / E-S complex to form;
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Describe one way that the lock and key model is different from the induced fit model. [1] - answersActive site does not
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change (shape) / is fixed (shape) / is rigid / does not wrap around substrate / (already) fits the substrate / is complementar
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(before binding);
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Explain why the rate of reaction of an enzyme is low away from its optimum pH. [3] - answers(change in pH) leads to
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breaking of bonds holding tertiary structure/ changes charge on amino acids; enzyme/protein/active site loses
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shape/denatured; substrate will not bind with/fit active site; fewer/no ES complexes formed;
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A protein molecule contains 150 amino acids. What is the total number of peptide bonds in this molecule? [1] - answers14
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How do you calculate magnification? [1] - answersM= I (Image)/ A (actual size)
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Describe the ways in which prokaryotic cells and eukaryotic cells differ. [3] - answersProkaryotic cells do not have a
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nucleus / have genetic material in cytoplasm; DNA in loop / ring; Not associated with proteins / do not have chromosome
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/chromatin / do not divide by mitosis; Smaller ribosomes; No membrane-bound organelles; Such as mitochondria /
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lysosomes / endoplasmic reticulum / Golgi / chloroplasts; Prokaryotic cells may have mesosomes; Prokaryotic cells
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smaller; May be enclosed by capsule;
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What is the function of: a)Ribosome b)Smooth ER c)Golgi apparatus d) Chloroplast e)Mitochondria [5] -
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answersa)Protein synthesis b)Lipid synthesis and transport c)Processing and packaging proteins for secretion
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d)Photosynthesis e)Aerobic respiration to produce ATP
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Explain the advantages and limitations of using a transmission electron microscope [5] - answersAdvantages: Small
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objects can be seen; TEM has high resolution as wavelength of electrons shorter; Limitations: Cannot look at living cells
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