Explain water's transport roles
Relate water's solvent action and high specific heat capacity to its roles in blood and tissue fluid.
AS Level; Cambridge International Biology 9700, 2028–2030. Written practice is self-checked; microscope recognition, biological drawing and supervised practical competence require practical work, while human subject-teacher review remains pending.
Before you begin
- Know that mass transport moves substances between exchange surfaces and cells, and that diffusion occurs down a concentration or partial-pressure gradient.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which water property helps carry dissolved ions in blood?
What you will learn
- State that water is the main component of blood and tissue fluid
- Relate solvent action and high specific heat capacity to mammalian transport
Build the explanation
Water is the main component of blood and tissue fluid. As a solvent, it allows many ions and polar molecules to be carried in solution, including nutrients and some waste products. Water's high specific heat capacity means that a relatively large amount of heat energy is needed to change its temperature. Blood can therefore distribute heat around the body while its temperature changes less rapidly than it would with a low-heat-capacity fluid.
Apply it carefully
Keep the two properties separate in an answer: solvent action explains carriage of dissolved substances; high specific heat capacity explains heat transfer with reduced temperature change. Not every transported substance is dissolved in plasma: oxygen is carried mainly bound to haemoglobin in red blood cells. Avoid saying water produces heat or that high specific heat capacity prevents all temperature change.
Pause and explain
How does high specific heat capacity help blood transport?
Worked example
How does water's solvent property support transport in blood?
Show the worked solution
- Identify that blood contains a large amount of water.
- State that dissolved ions and polar molecules can be carried in it.
Answer Water acts as a solvent, allowing many ions and polar molecules to be transported in blood plasma.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Distinguish how solvent action and high specific heat capacity support mammalian transport.
Give me a hint
One relates to dissolved materials; the other to heat.
Compare my reasoning
- Solvent action carries dissolved ions and polar substances.
- High specific heat capacity lets blood transfer heat with a relatively small temperature change.
Water dissolves many ions and polar molecules so they can be transported in blood and tissue fluid. Its high specific heat capacity allows blood to carry heat while its temperature changes relatively little.
Look for these in your work
- Dissolved substances linked to solvent
- Heat transfer linked to specific heat
- Properties kept distinct
A student says that oxygen dissolves in plasma because water is a solvent. Refine the statement for mammalian blood.
Give me a hint
Mention the principal oxygen carrier.
Compare my reasoning
- Some oxygen is dissolved in plasma.
- Most oxygen is transported reversibly bound to haemoglobin in red blood cells.
Water's solvent action supports transport of many dissolved substances, and a small amount of oxygen is dissolved in plasma. Most oxygen is transported reversibly bound to haemoglobin in red blood cells.
Look for these in your work
- Solvent role retained
- Main oxygen transport route correctly qualified
Blood absorbs heat from active muscle. Explain how its water content helps distribute that heat without claiming the temperature stays fixed.
Give me a hint
Use the phrase 'changes less rapidly', not 'does not change'.
Compare my reasoning
- Water has a high specific heat capacity.
- A substantial amount of energy is needed for a given temperature rise, so blood can carry heat with a smaller temperature change.
Because water has a high specific heat capacity, a relatively large amount of energy is needed to change the temperature of blood. Blood can transport heat from active muscle while its own temperature changes less rapidly; it is not held at a perfectly fixed temperature.
Look for these in your work
- Specific heat property stated
- Heat carried from tissue
- No absolute temperature claim
Common mistakes
- Using solvent action to explain heat transfer
- Claiming blood temperature cannot change
- Claiming most oxygen is dissolved in plasma
What can you explain now?
Which water property helps carry dissolved ions in blood?
Compare with the explanation
Solvent action
Substances that dissolve can be carried in the aqueous phase.
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Make it stick
Which water property supports dissolved-solute transport, and which supports heat transport?
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