Explain why the properties of water make it well suited to its role as a transport medium in living organisms.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Water is the main component of blood plasma, phloem sap, and many other transport fluids found in organisms.
Model answer (5 marks)
Water is a good solvent, so many substances dissolve in it.
This allows dissolved substances such as glucose, mineral ions and hormones to be carried in solution.
Water molecules are cohesive; they stick together.
Cohesion allows water to form a continuous column, which can be pulled up through xylem vessels.
Water has a high heat capacity, so it resists changes in temperature, keeping the temperature of the transport fluid stable and protecting enzymes from denaturation.
This allows dissolved substances such as glucose, mineral ions and hormones to be carried in solution.
Water molecules are cohesive; they stick together.
Cohesion allows water to form a continuous column, which can be pulled up through xylem vessels.
Water has a high heat capacity, so it resists changes in temperature, keeping the temperature of the transport fluid stable and protecting enzymes from denaturation.
Examiner tips
- Use the exact terms: solvent, dissolved substances, cohesion, continuous column, high heat capacity.
- Show the logical link between each property and its functional benefit.
- Keep each point brief and directly tied to the mark scheme points.
- Use bullet or numbered points if allowed to show structure.
Common mistakes
- Confusing adhesion with cohesion; only cohesion is required for xylem transport.
- Failing to mention that water’s high heat capacity stabilises enzyme activity.
- Writing vague statements like ‘water is good for transport’ without linking to specific properties.
Mark scheme (5 marks)
- Water is a good solvent / many substances dissolve in water
- This allows dissolved substances (e.g. glucose, mineral ions, hormones) to be carried / transported in solution
- Water molecules are cohesive / water molecules stick together / water has high cohesion
- Cohesion allows water to form a continuous column / allows water to be pulled up through xylem vessels
- Water has a relatively high heat capacity / resists changes in temperature, so temperature of transport fluid remains stable / enzymes in the fluid are not denatured
Key terms in this question
Related
- All AQA A-Level Biology (7402) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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