AQA A-level biology example essay 2022

,Describe how you would use a biochemical test to show that a solution contained a non -reducing
sugar, such as sucrose. [3] - ,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



1. Describe a chemical test you could carry out to show that a piece of coconut contains lipids. [3] -
(Crush in) ethanol / alcohol; Add (to) water (Order of adding is critical for this point); Emulsion /
white colour



2. Explain what is meant by a polymer. [1] - Molecule) made up of many identical/similar
molecules/monomers/ subunits;



3. Name the reaction which occurs when starch is broken down into maltose. [1] - Hydrolysis



4. What is the formula for lactose? [2] - C12 ; H22Ō1


5. Describe how β-glucose molecule differs from a molecule of α-glucose. [1] - H at top right end
(instead of OH) / OH at bottom (carbon 1)



6. Show two ways in which the structure of cellulose is different from the structure of starch. [2] -
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



7. Describe the structure of starch and explain how its structure is related to its function. [3] -
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;



8. The structure of a phospholipid molecule is different from that of a triglyceride. Describe how.
[2] - triglyceride has three fatty acids and phospholipid has two; no phosphate group present in
triglyceride but present in phospholipid.

, 9. What is an unsaturated fatty acid? [1] - Some / two carbons with only one hydrogen / (double
bonds) between carbon atoms / not saturated with hydrogen;



10. Describe the structure of cellulose and explain how its structure is relate d to its function. [3] -
Alternate β-glucose rotated 180o, long straight chains, Many hydrogen bonds join
(polysaccharide) chains/molecules to each other / makes microfibrils / gives tensile strength;



11. Which elements are found in proteins? [1] - Carbon, hydrogen, oxygen, nitrogen (sometimes
sulphur)



12. Describe how you would use a biochemical test to show that a solution contained protein. [2] -
Biuret / alkali + copper sulphate; Lilac/purple/mauve/violet;



13. Which bonds are found in a)Primary structure [1]b)Secondary structure [1] c)Tertiary structure
[2] - a)Peptide b) Hydrogen (and peptide) c)Ionic, disulphide bridges, hydrophobic interactions
(hydrogen and peptide)



14. Explain how a change in the primary structure of a globular protein may result in a different
three-dimensional structure. [3] - Sequence of amino acids changes; tertiary structure
changes/folds in a different way; bonds form in different places (not peptide);



15. Describe how two-way chromatography is carried out. [2] - Run chromatogram then turn
through 90/right angle; With a different solvent;



16. Explain the advantage of using two-way chromatography to separate short polypeptides. [2] -
Spreads spots/polypeptides out more/ make sure spot only contains one substance;



17. Explain how inhibitors affect the rate of enzyme-controlled reactions. [6] - 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;