Water
Cambridge A-Level Biology (9700) · Unit 2: Biological molecules · 8 flashcards
Water is topic 2.4 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 2 — Biological molecules , alongside Testing for biological molecules, Carbohydrates and lipids and Proteins. In one line: A solvent is a substance that dissolves a solute, resulting in a solution. Water is an excellent solvent due to its polarity, which allows it to form hydrogen bonds with, and thus dissolve, many polar and ionic substances such as glucose and salts.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 8 flashcards — 3 definitions and 5 key concepts — covering the precise wording mark schemes reward. Use the 3 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
The term 'solvent' and explain why water is an effective solvent
A solvent is a substance that dissolves a solute, resulting in a solution. Water is an excellent solvent due to its polarity, which allows it to form hydrogen bonds with, and thus dissolve, many polar and ionic substances such as glucose and salts.
What the Cambridge 9700 syllabus says
2025-2027 syllabus, in our words · AS LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Explain how hydrogen bonds form between water molecules, and relate water's properties to the roles it plays in organisms, limited to three properties: its high specific heat capacity, its latent heat of vaporisation and its action as a solvent.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9700 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Water
- › Use scientific descriptions: state that hydrophobic molecules are non-polar, insoluble in water, and unable to form hydrogen bonds with water molecules.
Explain how hydrogen bonds form between water molecules.
Hydrogen bonds form due to the slight negative charge (δ-) on the oxygen atom and slight positive charge (δ+) on the hydrogen atoms within a water molecule. This polarity arises from oxygen's higher electronegativity. The δ+ hydrogen of one water molecule is attracted to the δ- oxygen of another, forming a hydrogen bond.
Define the term 'solvent' and explain why water is an effective solvent.
A solvent is a substance that dissolves a solute, resulting in a solution. Water is an excellent solvent due to its polarity, which allows it to form hydrogen bonds with, and thus dissolve, many polar and ionic substances such as glucose and salts.
Explain how water's solvent properties are important in living organisms.
Water's solvent properties allow for the transport of essential substances (
Define 'specific heat capacity' and explain why water has a high specific heat capacity.
Specific heat capacity is the amount of heat energy required to raise the temperature of 1 gram of a substance by 1 degree Celsius. Water has a high specific heat capacity because hydrogen bonds between water molecules require a lot of energy to break or weaken, limiting temperature increases.
Explain the biological significance of water's high specific heat capacity.
Water's high specific heat capacity helps maintain stable internal temperatures in organisms and aquatic environments. This prevents rapid temperature fluctuations that could harm biological processes.
Define 'latent heat of vaporisation' and explain why water has a high latent heat of vaporisation.
Latent heat of vaporisation is the amount of heat energy required to change 1 gram of a liquid into a gas at its boiling point. Water has a high latent heat of vaporisation due to the strong hydrogen bonds that must be broken to allow water molecules to escape as gas.
Explain how water's high latent heat of vaporisation is important for thermoregulation in living organisms.
Evaporation of water, such as sweat in mammals or transpiration in plants, requires a large amount of heat energy. This cools the organism as the heat is taken away from the body, providing an effective cooling mechanism.
Describe an example of how water's properties contribute to the transport of nutrients in plants.
Water acts as a solvent to dissolve mineral ions in the soil, which are then transported up the xylem vessels from the roots to the leaves through transpiration. Water's cohesive properties, due to hydrogen bonding, allow for the continuous water column needed for transpiration.
Review the material
Read full revision notes on Water — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 2 — Biological molecules
Water sits alongside these A-Level Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Water deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
How to study this Water deck
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