OCR A 2.1.2(k)–(s) · 20 written questions · 43 marks · about 50 minutes · marked as you go
This free quiz has 20 written exam questions on proteins, ions, food tests and chromatography, all taken from OCR A Level Biology A papers (AS and A level, 2018 to 2025). Short answers and calculations mark themselves. For longer answers you write your answer, then tick off the OCR mark-scheme points you made, so you see exactly where the marks are. The quiz covers the second half of OCR A 2.1.2 Biological molecules: amino acids and protein structure, globular and fibrous proteins, the key inorganic ions, the practical food tests and colorimetry, and paper and thin layer chromatography.
What the quiz covers (OCR A spec 2.1.2(k)–(s))
Amino acids and peptide bonds (2.1.2(k)(l)): the groups in an amino acid and how proteins are broken down by hydrolysis.
Levels of protein structure (2.1.2(m)): disulfide bonds, quaternary structure and how to read protein diagrams.
Globular and fibrous proteins (2.1.2(n)(o)): haemoglobin as a conjugated protein, enzyme terms for catalase, and the properties of collagen.
Inorganic ions (2.1.2(p)): formulae and roles of nitrate, phosphate and hydroxide ions.
Food tests and colorimetry (2.1.2(q)(r)): Benedict's, iodine and biuret tests, testing for non-reducing sugars, and using a colorimeter and calibration curve.
Chromatography (2.1.2(s)): calculating Rf values, the role of the solvent, visualising colourless spots and identifying unknowns.
How to use it
Write every answer in full, as you would in the exam: the mark for each question is shown, so you know how much to write. When you self-mark, only tick a point if your answer clearly makes it, then read the examiner's tip under each question. Your progress is saved on your device, so you can do it in two sittings, and at the end you can retry just the questions where you dropped marks.
Prefer multiple choice? Try the 17-question Amino Acids and Proteins multiple choice quiz first.
Open the Proteins, Ions, Food Tests and Chromatography quiz in a new tab (easier on a phone)
Where students lose marks (from OCR examiners' reports and mark schemes)
Each point below is followed by wording that gained marks.
Peptide bonds form by condensation: Students mix up the two reactions, saying peptide bonds are formed by hydrolysis or broken by condensation.
✔ Gains credit: A peptide bond forms in a condensation reaction (water is released) and is broken by hydrolysis (water is added).
Carboxyl, not hydroxyl: The acid group of an amino acid is called a hydroxyl group, or the amine group is called 'nitrogenous' or an amide.
✔ Gains credit: An amino acid has an amine (amino) group and a carboxyl (carboxylic acid) group.
Check which residues the bond joins: A bond linking two cysteines in a folded protein is called a peptide bond, even though they aren't next to each other in the chain.
✔ Gains credit: A disulfide bond (bridge) forms between the R groups of two cysteines.
Use the figure for quaternary: Students define quaternary structure as 'more than one' polypeptide chain instead of using the evidence in the diagram.
✔ Gains credit: The figure shows two polypeptide chains joined together by disulfide bonds between cysteines on different chains.
Non-reducing sugars need acid first: Students forget that sucrose gives a negative Benedict's test until it has been hydrolysed, or call sucrose a reducing sugar.
✔ Gains credit: Do Benedict's test first; if it is negative, boil a sample with dilute hydrochloric acid to hydrolyse it into monosaccharides, then retest with Benedict's.
Red filter is for Benedict's: When using a colorimeter with biuret reagent, students choose a red filter, which suits Benedict's but not a purple solution.
✔ Gains credit: Zero the colorimeter, make a calibration curve from known concentrations, measure the unknown's absorbance and read it off, using a filter suited to the purple colour.
Convert concentration units carefully: Changing mmol cm⁻³ to mmol dm⁻³, students forget to convert or divide by 1000 instead of multiplying.
✔ Gains credit: A dm³ holds 1000 times more solution than a cm³, so the number of mmol per dm³ is 1000 times bigger.
Rf divides by the solvent front: Rf is calculated upside down (solvent ÷ spot), the wrong spot is measured, or the answer is given to too many significant figures.
✔ Gains credit: Rf = distance moved by the spot ÷ distance moved by the solvent front, both from the origin, to 2 significant figures.
Keep practising
Try the Amino Acids and Proteins multiple choice quiz, the Food Tests and Chromatography quiz, the Water, Carbohydrates and Lipids written quiz or the Nucleotides, DNA and Protein Synthesis written 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.
Questions, mark schemes and examiners' report extracts © OCR.