This free quiz has 20 multiple choice questions on biochemistry (bonds, reactions, food tests and chromatography), all taken from OCR A Level Biology A exam papers. It marks itself, so you get your score as soon as you finish.
What the quiz covers (OCR A spec 2.1.2)
Benedict's test and the colours it gives
Identifying carbohydrates, lipids and proteins from their elements
Naming reactions: condensation, hydrolysis, oxidation and reduction
The bonds in haemoglobin, collagen, triglycerides and RNA
Glycosidic bonds in disaccharides and polysaccharides, and the products of hydrolysis
Recognising monosaccharide structures and hydrophobic R groups
Buffers, chromatography, and how many dipeptides 20 amino acids can make
How to use it
Do it without notes first: these questions test recall. Before you start, make a quick table of each bond, the two molecules it joins and the reaction that makes or breaks it.
Where students lose marks (from OCR examiners' reports and mark schemes)
Each point below is followed by wording that gained marks.
Amino acid groups and R groups: Students left the CH2 out when circling an R group, called the carboxyl group a 'hydroxyl', or used a carbon in the R group as the central carbon when completing an amino acid.
✔ Gains credit: an amine group (NH2) and a carboxyl group (COOH) on the central carbon, with the R group attached to that same carbon; the whole R group circled, including the CH2 above the alpha carbon.
Monosaccharide structure details: Many students placed the ring O and the groups on carbon 1 correctly but fewer got the group on carbon 6 right, and a common error was thinking ribose is a hexose.
✔ Gains credit: in alpha glucose the OH on carbon 1 is below the ring, with the ring oxygen and the CH2OH group in their correct positions; ribose is not a hexose monosaccharide (it is a pentose).
Compare polysaccharides precisely: When comparing polysaccharides, students wrote that they 'are hexose sugars' rather than contain them, said only that both have glycosidic bonds, or did not say which polymer each difference referred to. Some swapped starch and cellulose features completely.
✔ Gains credit: both are polysaccharides that contain 6-carbon (hexose) sugars joined by 1-4 glycosidic bonds; chitin contains nitrogen (an NH–CO–CH3 group) and has no 1-6 bonds or branching, whereas glycogen does.
Measuring and rounding Rf values: Marks were lost by measuring to the end of the plate instead of the solvent front, measuring the wrong spot, dividing the wrong way round, ignoring the units on the answer line, or giving too many significant figures.
✔ Gains credit: Rf = distance from origin to the centre of the spot divided by distance from origin to the solvent front, rounded as asked, e.g. 91 mm divided by 109 mm = 0.83 to 2 significant figures.
What Rf says about R groups: Asked what a chromatogram shows about amino acids, many students just said the Rf values or 'chemical properties' were similar or different, or described R groups as bigger, smaller or more hydrophilic.
✔ Gains credit: the R groups differ in polarity, charge or functional groups (e.g. serine is more polar than leucine); amino acids with similar Rf values have similar R groups and similar interactions with the stationary phase.
TLC stationary phase and standards: Many students named paper or a solvent as the stationary phase in TLC, and when identifying pigments by colour they often did not say what the colours should be compared with.
✔ Gains credit: silica gel (or alumina) as the TLC stationary phase; run known pigments on the same plate with the same solvent and compare positions or colours; data book Rf values may not match if a different solvent, plate or temperature was used.
Zeroing and calibrating a colorimeter: Few students said a blank of distilled water is used to set the colorimeter to zero absorbance, often suggesting 'a clear liquid' or just pressing a button; when asked for another way to measure protein concentration, many named Benedict's test or a titration.
✔ Gains credit: set the colorimeter to zero absorbance with distilled water, measure solutions of known concentration, plot a calibration curve of absorbance against concentration and read the unknown from it; a biosensor is an alternative method.
Keep practising
Go on to the Biological Molecules quiz, the Carbohydrates quiz or the Water, Ions and Elements quiz, or browse all our OCR A Level Biology quizzes. Our OCR A masterclasses (Year 12 on Wednesdays at 5.15pm, Year 13 on Tuesdays at 6.30pm) work through real exam questions on one topic each week.
Practising recall is so important for retention and learning. Try this quiz without books first !
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