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Practice · Biology · 2025 syllabus · A2.1

IB Biology A2.1 Origins of cells: practice questions

4 exam-style questions on A2.1 Origins of cells, 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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A2.1-01 · Paper 1A style · multiple choice · 1 mark · HL

Conditions on pre-biotic Earth

Which describes conditions on Earth before life began, compared with conditions today? [1]

  1. No free oxygen, no ozone layer, and more carbon dioxide and methane
  2. No free oxygen, a thicker ozone layer, and less carbon dioxide
  3. More free oxygen, no ozone layer, and more methane
  4. No free oxygen, no ozone layer, and lower temperatures due to less carbon dioxide
Show the answer and the reasoning

Answer: A. Free oxygen only accumulated after photosynthesis evolved, and ozone forms from oxygen, so early Earth had neither; ultraviolet light therefore reached the surface. Carbon dioxide and methane were more concentrated, which kept temperatures high. B is impossible because an ozone layer cannot form without oxygen. C gets oxygen the wrong way round. D is right about oxygen and ozone but wrong about carbon dioxide and temperature: both were higher.

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The 4 questions in A2.1

  1. A2.1-01 Conditions on pre-biotic EarthPaper 1A style · multiple choice · 1 mark · HL
  2. A2.1-02 Evaluating the Miller-Urey experimentPaper 1A style · multiple choice · 1 mark · HL
  3. A2.1-03 Evidence for an RNA worldPaper 1A style · multiple choice · 1 mark · HL
  4. A2.1-04 Searching for LUCAPaper 2 style · short answer · 5 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.