IB Biology SL B1.2 Proteins Questions

Practise IB Biology SL B1.2 proteins through amino acid structure, peptide bonds, condensation reactions, dietary requirements and structure–function links.

39 questions in this syllabus scope, with question parts counted together.

Syllabus
First assessment 2025
Course
Biology SL
Level
SL

Exam analysis

SL · 2010–2025
Papers with this topic49 / 141in the analysed sample
Latest appearanceNovember 2025
Tagged question parts57
Paper types5

Most tested objectives

  1. B1.2.2—Condensation reactions14 papers
  2. B1.2.3—Dietary amino acids12 papers
  3. B1.2.10 (HL)—Effect of polar/non-polar amino acids7 papers
  4. B1.2.12 (HL)—Globular vs. fibrous proteins7 papers
  5. B1.2.1—Generalized amino acid structure6 papers

Common question formats

  • Definition or recall
  • Diagram interpretation
  • Process explanation
  • Structured response
  • Comparison
  • Data analysis

Recent exam appearances

November 2025Paper 2 SL · TZ1Q2(a)[ 2 ]
May 2025Paper 1A SL · TZ3Q4[ 1 ]
May 2025Paper 1A SL · TZ2Q3[ 1 ]

141 papers analysed · Tagging incomplete

Exam points

  • Identify an amino acid’s alpha carbon, amine group, carboxyl group, hydrogen and variable R-group, and relate protein composition to C, H, O, N and usually S.
  • Explain amino-acid condensation and peptide-bond formation, identify dipeptide or polypeptide products and water release, and distinguish condensation from hydrolysis.
  • Distinguish essential amino acids that must come from dietary protein from non-essential amino acids made by the body, and explain limiting supply and protein-deficiency consequences.
  • Explain how amino-acid type, number and order create a wide variety of polypeptide sequences and proteomes.
  • Explain how high temperature or unsuitable pH denatures proteins by changing their structure and reducing biological activity.

Covered syllabus points

B1.2.1—Generalized amino acid structureB1.2.2—Condensation reactionsB1.2.3—Dietary amino acidsB1.2.4—Infinite variety of peptide chainsB1.2.5—Effect of pH and temperature

Exam points

  • Draw an amino acid with the alpha carbon bonded to amine, carboxyl, H and R-group.
  • Identify proteins as the biological molecules that may contain sulfur.

Question 1

[Maximum number: 3]

Draw a molecular diagram of an amino acid to show its general structure.

Exam points

  • Mark the peptide bond between C=O and N-H groups in a dipeptide or polypeptide diagram.
  • Show condensation between amino acids, with peptide-bond formation and water release.
  • Calculate peptide bonds from amino-acid totals and the number of separate polypeptide chains.
  • Identify ribosomes as the site where amino acids are joined into polypeptide chains.

Question 1

[Maximum number: 1]

How are amino acids joined together to form a dipeptide?

A

Single bond between a carbon and a hydrogen

B

Hydrolysis reaction forming a hydrogen bond

C

Anabolism forming a double bond

D

Condensation reaction forming a peptide bond

Exam points

  • Distinguish amino acids that must come from food from non-essential amino acids made by the body.
  • Compare essential-amino-acid data across foods or diets to judge dietary adequacy.
  • Use a vegan-diet scenario or amino-acid table to identify what must be supplied.
  • Explain how inadequate essential amino acids or protein can limit growth and cause malnutrition.

Question 1

[Maximum number: 1]

What must vegans ensure when they plan their diet?

A

Higher protein consumption than meat-eaters

B

Sufficient quantities of all essential amino acids are consumed

C

Only proteins with all 20 amino acids are consumed

D

Higher fat consumption than meat-eaters

Exam points

  • Trace how codon order specifies amino-acid order and how sequence variation creates many polypeptides.
  • Define a proteome as a cell’s expressed proteins and distinguish it from the shared genome.
  • Interpret why one genome can produce different proteomes or more protein types than gene count.

Question 1

[Maximum number: 7]

Cells produce a large variety of proteins with different sequences of amino acids. Explain how this is done.

Exam points

  • Identify heat, unsuitable pH, salts or heavy metals as causes of protein denaturation.
  • Explain how pH changes alter an enzyme’s active site and reduce substrate binding or activity.
  • Define denaturation as a change in protein three-dimensional shape that can remove biological activity.

Question 1

[Maximum number: 2]

Two models of plasma membrane structure are shown.

Figure for Question 1 — IB Biology SL

Phospholipase C is an enzyme that digests the polar heads of phospholipids. Scientists used phospholipase C to test these models of membrane structure. They found that the enzyme could digest the heads of phospholipids in the plasma membranes of red blood cells.

Suggest one reason for maintaining a pH of 7.5 throughout the experiment.