OCR A Level Chemistry B (Salters)
OCR A Level Chemistry B Polymers and Life (PL) Exam Questions
Free OCR A Level Chemistry B exam questions for Polymers and Life (PL), with a mark scheme for every pack. Covers amino acids, zwitterions, peptides, protein structure, hydrolysis, optical isomerism, condensation polymers, polyesters, polyamides, DNA and enzyme action.
Polymers and Life (PL) exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About OCR A Level Chemistry B Polymers and Life (PL)
Polymers and Life is a Year 2 storyline of OCR A Level Chemistry B (Salters) linking organic chemistry to the molecules of living things. It covers amino acids, zwitterions, peptide bonds and the levels of protein structure, along with hydrolysis of proteins and chromatography of amino acids. Optical isomerism explains why most amino acids are chiral. Condensation polymers such as polyesters and polyamides are compared with natural polymers, and the structure of DNA and the action of enzymes are explained in terms of intermolecular bonds. Examiners frequently ask you to draw peptide links and repeat units, explain enzyme specificity and identify chiral centres.
What you need to know
- Amino acids Amino acids have an NH2 group and a COOH group on the same carbon. In solution they exist as zwitterions; in acid they are protonated and in alkali deprotonated.
- Peptides and proteins Amino acids join by condensation to form peptide (amide) links. Primary structure is the sequence; secondary structure (alpha helix, beta sheet) is held by hydrogen bonds; tertiary structure involves hydrogen bonds, ionic interactions, disulfide bridges and instantaneous dipole-induced dipole bonds.
- Hydrolysis and chromatography Proteins are hydrolysed by heating with hydrochloric acid; the amino acids can be separated by paper or thin-layer chromatography and identified by Rf values.
- Optical isomerism A carbon with four different groups is chiral, giving two non-superimposable mirror images that rotate plane-polarised light in opposite directions. All amino acids except glycine are chiral.
- Condensation polymers Polyesters (from diols and dicarboxylic acids) and polyamides (from diamines and dicarboxylic acids) form with loss of a small molecule such as water. They can be hydrolysed back to monomers.
- DNA and enzymes DNA is a double helix held by hydrogen bonds between complementary base pairs. Enzymes are protein catalysts with active sites; substrates bind specifically, and enzymes are denatured by high temperature or extreme pH.
Common mistakes in Polymers and Life (PL)
- Drawing the peptide link the wrong way or with the C=O on the nitrogen.
- Saying a protein's tertiary structure is held only by covalent bonds. Most interactions are hydrogen bonds, ionic interactions and other intermolecular bonds, plus disulfide bridges.
- Calling glycine chiral. Its central carbon has two hydrogen atoms.
- Describing enzyme denaturation as the enzyme being killed. The active site changes shape because intermolecular bonds break.
- Forgetting to show open bonds at each end of a polymer repeat unit.
Try three Polymers and Life (PL) exam-style questions
1. Glycine (Mr 75.0) and alanine (Mr 89.0) form a dipeptide. Calculate the Mr of the dipeptide and name the type of reaction. (2 marks)
Show the mark scheme answer
75.0 + 89.0 - 18.0 = 146.0; condensation (water eliminated).
2. Explain why heating an enzyme to a high temperature reduces its activity. (3 marks)
Show the mark scheme answer
Heat breaks the hydrogen bonds and other weak bonds that hold the tertiary structure; the shape of the active site changes; so the substrate no longer fits and binds, and the enzyme is denatured.
3. Explain why alanine, CH3CH(NH2)COOH, exists as two optical isomers. (2 marks)
Show the mark scheme answer
The central carbon is bonded to four different groups (H, CH3, NH2, COOH); so it has two non-superimposable mirror image forms.
Polymers and Life (PL) FAQs
What does OCR A Level Chemistry B Polymers and Life (PL) cover?
It covers amino acids and zwitterions, peptides and protein structure, hydrolysis and chromatography of amino acids, optical isomerism, condensation polymers, DNA structure and enzyme action.
Which papers is Polymers and Life examined in?
In the Salters A Level, content from any storyline can be assessed in all three papers: Fundamentals of chemistry, Scientific literacy in chemistry and Practical skills in chemistry.
How should I revise protein structure for PL?
Learn each level of structure with the bonds or interactions that hold it, practise drawing peptide links and repeat units, and connect tertiary structure to the shape of an enzyme's active site.
