IB Biology A1.1 Water: practice questions

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A1.1-02 · Paper 1A style · multiple choice · 1 mark

Hanging from the surface film

Mosquito larvae hang just beneath the surface of still ponds, supported by the surface film while they breathe air through a tube at the tip of the abdomen. What allows the surface film to support them? [1]

1. Hydrogen bonds between neighbouring water molecules make the water cohesive, so the surface resists being broken.
2. Water adheres to the body of the larva, so capillary action draws the larva upwards.
3. The high specific heat capacity of water keeps the surface layer cool and therefore denser.
4. Covalent bonds join the water molecules at the surface into a continuous sheet.

Show the answer and the reasoning

Answer: A. Each water molecule is polar, so it forms hydrogen bonds with its neighbours. At the surface these attractions pull the molecules together, and this cohesion gives the surface tension that supports a small, light organism. B confuses cohesion with adhesion: adhesion is attraction to a different material, and capillary action moves water along narrow spaces rather than holding an object up. C is wrong because specific heat capacity concerns how much energy is needed to change the temperature of water, not the strength of its surface. D is wrong because covalent bonds hold the atoms together inside each water molecule; the bonds between molecules are hydrogen bonds.

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The 5 questions in A1.1

1. A1.1-01 Bonds within and between moleculesPaper 1A style · multiple choice · 1 mark
2. A1.1-02 Hanging from the surface filmPaper 1A style · multiple choice · 1 mark
3. A1.1-03 Living in water versus airPaper 1A style · multiple choice · 1 mark
4. A1.1-04 A diving bird and its mediumPaper 2 style · short answer · 6 marks
5. A1.1-05 Heat loss in water and airPaper 1B style · data-based · 9 marks

More of A Unity and diversity

• A1.2 Nucleic acids
• A2.1 Origins of cells
• A2.2 Cell structure
• A2.3 Viruses
• A3.1 Diversity of organisms
• A3.2 Classification and cladistics
• A4.1 Evolution and speciation
• A4.2 Conservation of biodiversity

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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.