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Practice · Biology · 2025 syllabus · C3.1

IB Biology C3.1 Integration of body systems: practice questions

6 exam-style questions on C3.1 Integration of body systems, SL and HL, 2 marked HL: 3 multiple choice, 1 data-based, 1 short answer and 1 extended response. Each one comes with the mark scheme, a model answer and the reasoning behind every mark. Free with your email.

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C3.1-01 · Paper 1A style · multiple choice · 1 mark

Melatonin secretion

Which describes the secretion of melatonin in humans? [1]

  1. Secreted by the pituitary gland, mainly during daylight
  2. Secreted by the adrenal glands, mainly during exercise
  3. Secreted by the pineal gland, mainly during darkness
  4. Secreted by the pineal gland, mainly during daylight
Show the answer and the reasoning

Answer: C. C is correct. Melatonin is secreted by the pineal gland; secretion rises in the evening as light fades and peaks during the night, helping to bring on sleep, then falls towards morning. A names the wrong gland and the wrong time. B describes epinephrine (adrenaline), which prepares the body for vigorous activity. D has the right gland but reverses the pattern: light suppresses melatonin secretion.

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The 6 questions in C3.1

  1. C3.1-01 Melatonin secretionPaper 1A style · multiple choice · 1 mark
  2. C3.1-02 Parts of a pain reflex arcPaper 1A style · multiple choice · 1 mark
  3. C3.1-03 Direction of auxin transportPaper 1A style · multiple choice · 1 mark · HL
  4. C3.1-04 Melatonin and light at nightPaper 2 style · short answer · 6 marks
  5. C3.1-05 Phototropism and auxin transportPaper 1B style · data-based · 9 marks · HL
  6. C3.1-06 Coordinating the body in a sprintPaper 2 style · extended response · 15 marks

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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.