IB Biology D3.1 Reproduction: practice questions

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D3.1-01 · Paper 1A style · multiple choice · 1 mark

Events at fertilization

Which event is part of fertilization in humans? [1]

1. The sperm’s tail and mitochondria are kept and go on functioning in the zygote.
2. The cell membranes of the sperm and the egg fuse, and the sperm nucleus enters the egg.
3. The chromosomes from the sperm and the egg pair up and then divide by meiosis.
4. The two nuclei merge, their membranes joining to form one large diploid nucleus.

Show the answer and the reasoning

Answer: B. B is correct. At fertilization the sperm’s cell membrane fuses with the egg’s cell membrane and the sperm nucleus passes into the egg. A is wrong because the sperm’s tail and mitochondria are destroyed, so all the zygote’s mitochondria come from the egg. C is wrong because the zygote divides by mitosis; meiosis happened earlier, when the gametes were made. D is wrong because the two nuclear membranes dissolve rather than merge: the condensed chromosomes from both gametes then take part in a joint mitosis that produces two diploid nuclei.

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The 6 questions in D3.1

1. D3.1-01 Events at fertilizationPaper 1A style · multiple choice · 1 mark
2. D3.1-02 Where plant gametes formPaper 1A style · multiple choice · 1 mark
3. D3.1-03 Stigma ready before pollenPaper 1A style · multiple choice · 1 mark
4. D3.1-04 Halving and doubling in a life cyclePaper 2 style · short answer · 7 marks
5. D3.1-05 Inbred and outbred seedlingsPaper 1B style · data-based · 9 marks
6. D3.1-06 Gametes and reproductive hormonesPaper 2 style · extended response · 15 marks · HL

More of D Continuity and change

• D1.1 DNA replication
• D1.2 Protein synthesis
• D1.3 Mutation and gene editing
• D2.1 Cell and nuclear division
• D2.2 Gene expression
• D2.3 Water potential
• D3.2 Inheritance
• D3.3 Homeostasis
• D4.1 Natural selection
• D4.2 Stability and change
• D4.3 Climate change

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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.