AQA Biology Mark Scheme Notes
These are for AS only covering Topics 1-8
This does not cover all of the content. It only covers questions which have been asked on past papers and their answers.
A Level Biology is very mark scheme specific so this document can massively increase your grades.
This...
AQA Biology Mark Scheme Notes
These are for AS only covering Topics 1-4
This does not cover all of the content. It only covers questions which have been asked on
past papers and their answers.
A Level Biology is very mark scheme specific so this document can massively increase your
grades.
This can be used for all AS exams and A level exams paper 1 and 3.
I suggest using this document to revise.
If you prefer you can write these down on flashcards or use them on quizlet or anki.
Good luck!
Topic 1 Biological Molecules
1.1 What is a monomer?
● A smaller molecule from which larger molecules called polymers are
made.
1.2 What are the products of the hydrolysis of sucrose?
● Glucose.
● Fructose.
1.2 Describe how lactose is formed and where in the cell it would be attached to
a polypeptide to form a glycoprotein?
● By glucose and galactose.
● Joined by a condensation reaction.
● Also joined by a glycosidic bond.
● Added to a polypeptide in the Golgi apparatus.
1.2 Describe the test for amylase?
● Add biuret reagent and it becomes purple/lilac.
● Add starch,leave for some time, test for reducing sugar/absence of starch.
,1.2 How is the structure of glycogen related to its function?
● It is helix/branched so it’s compact.
● It’s a polymer of glucose so it’s easily hydrolysed.
● It’s branched so it has more ends for faster hydrolysis.
● It’s a glucose polymer so it provides a respiratory substrate for energy
release.
● Insoluble so it does not affect the water potential /osmosis.
1.2 Describe the structure of glycogen?
● A polysaccharide of α-glucose.
● Joined by glycosidic bonds.
1.2 Suggest how glycogen acts as a source of energy?
● Hydrolysed to release glucose.
● Glucose is used in respiration.
1.2 How is the structure of starch molecules are related to its
function?
● Has a helical/spiral shape so it’s compact.
● Is a large molecule which is insoluble so it’s osmotically inactive.
● It’s branched so glucose is easily released for respiration.
● It’s a large molecule so it cannot leave the cell.
● It’s insoluble so it doesn’t affect the water potential.
1.2 Describe and explain the features of starch that make it a good storage
molecule?
● It’s insoluble in water so it doesn’t affect the water potential.
● It’s branched/coiled α-helix so it makes the molecule compact.
● Polymer of α-glucose so provides glucose for respiration.
● It is branched/ has more ends for a fast breakdown of enzyme action.
● Is a large molecule so it can’t cross the cell membrane.
1.2 How is the structure of cellulose molecules related to its function?
● It’s joined by hydrogen bonding to form micro/macro fibrils.
● Provides rigidity/strength to the cell wall.
● Has long, straight unbranched chains of β glucose.
,1.2 Describe the differences between the structure of a cellulose molecule and a
glycogen molecule?
● Cellulose is made up of β-glucose monomers and glycogen is made up of
α-glucose monomers.
● Cellulose molecule is a straight chain and glycogen is branched.
● Cellulose molecule is a straight chain and glycogen is coiled.
● Glycogen has 1,4- and 1,6- glycosidic bonds and cellulose has only 1,4-
glycosidic bonds.
1.2 Describe a biochemical test for a non-reducing sugar?
● Do the Benedict’s test and the colour stays blue/negative.
● Heat/boil with acid and neutralise with the alkali.
● Then heat with Benedict’s solution and a positive result will show a red
precipitate/colour.
1.3 Describe how a triglyceride molecule is formed?
● One glycerol and three fatty acids.
● By condensation reactions and the removal of three molecules of water.
● So ester bonds are formed.
1.3 How is an ester bond formed in a phospholipid molecule?
● By a condensation reaction due to a loss of water.
● Between glycerol and a fatty acid.
1.3 Name the group represented by COOH?
● Carboxyl.
1.3 What is the difference between the structure of a triglyceride molecule and
the structure of a phospholipid molecule?
● In phospholipid, one fatty acid is replaced by a phosphate.
1.3 How do you test for lipids?
● Add ethanol, then add water and then shake/mix.
● A positive result shows a white/milky emulsion.
1.3 What is the difference between a saturated and an unsaturated fatty acid?
, ● A saturated fatty acid has no double bonds between carbons whereas
unsaturated fatty acid has at least one double bond between carbons.
1.3 Compare and contrast the structure and properties of triglycerides and
phospholipids?
Similar -
● Both contain ester bonds between glycerol and fatty acid.
● Both contain glycerol.
● Both are insoluble in water.
● Both have fatty acids which may be saturated or unsaturated.
Differences -
● Both contain C,H and O but phospholipids also contain P.
● Triglyceride has three fatty acids and phospholipid has two fatty acids plus
a phosphate group.
● Triglycerides are hydrophobic/non-polar and phospholipids have a
hydrophilic and hydrophobic region.
● Phospholipids form monolayer on the surface/bilayer in water but
triglycerides don’t.
1.4.1 How are all dipeptides similar and how might they differ?
Similar -
● All have the Amine/NH2 group at the end.
● All have the Carboxyl/COOH group at the end.
● All have 2 R groups.
● All contain C and H and N and O.
Differ -
● Have a variable/different R groups.
1.4.1 Describe how a peptide bond is formed between two amino acids to form a
dipeptide?
● Condensation reaction so there is a loss of water.
● Between amine / NH2 and carboxyl / COOH.
1.4.1 Describe how the structure of a protein depends on the amino acids it
contains?
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