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Practice · Biology · 2025 syllabus · C2.1

IB Biology C2.1 Chemical signalling: practice questions

4 exam-style questions on C2.1 Chemical signalling, HL only: 3 multiple choice and 1 short answer. Each one comes with the mark scheme, a model answer and the reasoning behind every mark. Free with your email.

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C2.1-01 · Paper 1A style · multiple choice · 1 mark · HL

Steroid hormone action

Testosterone is a steroid hormone. Which sequence of events follows its arrival at a target cell? [1]

  1. Diffuses through the membrane → binds a receptor in the cytoplasm or nucleus → hormone-receptor complex binds to DNA → target genes transcribed
  2. Binds a receptor in the plasma membrane → G protein activated → cAMP produced → cascade of protein kinases activated
  3. Diffuses through the membrane → binds directly to DNA → receptor in the nucleus activated → target genes transcribed
  4. Binds a receptor in the plasma membrane → tyrosine phosphorylated inside the cell → glucose transporters moved to the membrane
Show the answer and the reasoning

Answer: A. A is correct. Steroids are hydrophobic, so testosterone diffuses through the phospholipid bilayer and binds a receptor protein in the cytoplasm or nucleus. Binding activates the receptor, and the hormone-receptor complex attaches to particular DNA sequences, increasing transcription of the target genes. B is the epinephrine pathway, which uses a G protein-coupled receptor at the cell surface and cAMP as a second messenger; a steroid does not need a surface receptor because it can cross the membrane. C has the hormone binding DNA by itself: the hormone must first bind and activate its receptor, and it is the complex that recognises the DNA. D describes the insulin receptor, which has tyrosine kinase activity and leads to glucose transporters being moved to the plasma membrane.

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The 4 questions in C2.1

  1. C2.1-01 Steroid hormone actionPaper 1A style · multiple choice · 1 mark · HL
  2. C2.1-02 Quorum sensing in a mutantPaper 1A style · multiple choice · 1 mark · HL
  3. C2.1-03 Categories of signalling chemicalsPaper 1A style · multiple choice · 1 mark · HL
  4. C2.1-04 Blocking the epinephrine pathwayPaper 2 style · short answer · 7 marks · HL

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Every Biology and Chemistry question here is original, written for practice in the style of the papers set since the 2025 syllabus, with invented data. Developed independently from the International Baccalaureate Organization, which has not endorsed it. Found a mistake? Email vytis@limeadmissions.com with the question id.