Explain water sources and body functions
Connect water to transport, reactions and temperature regulation.
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Recall large and small nutrient molecules, cell membranes and enzyme specificity.
- Use the stated diagram keys and evidence; models are not to scale.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is a solvent?
What you will learn
- Connect water to transport, reactions and temperature regulation.
- Distinguish a water source from absorption across the gut.
Water is a medium rather than a fuel
| Component | Examples of sources | Role |
|---|---|---|
| Water | Drinks; water-containing foods | Solvent, transport and reaction medium |
Water comes from more than drinks
Drinking water and other drinks supply water, and many foods such as fruit, vegetables and soups also contain it. Water is an essential dietary component, but it is not an energy-yielding fuel.
Water acts as a solvent and medium for many reactions. It supports transport in blood plasma and other body fluids. A substance dissolved in water is not the same as the water molecules themselves.
Relate functions without inventing targets
Water also contributes to temperature regulation, including evaporative cooling when sweat evaporates. This is a different function from haemoglobin carrying oxygen. The lesson describes biological functions rather than prescribing a universal daily volume.
Water is absorbed from the digestive system; most absorption occurs in the small intestine, with some in the colon. Do not confuse drinking water with the later movement across a gut wall.
Sources for this lesson
Pause and explain
Which is a water function?
Worked example
A supplied diagram shows glucose dissolved in blood plasma. State a water-related transport role.
Show the worked solution
- Identify water as a solvent.
- Distinguish dissolved glucose from solvent water.
- Connect the fluid medium to transport.
Answer Water provides a solvent medium in which substances such as glucose can be transported.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
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.
Name two dietary water sources and two functions.
Give me a hint
Include a food as well as a drink.
Compare my reasoning
- Name water and soup.
- State solvent/transport and reaction medium.
Drinking water and soup; water is a solvent for transport and a medium for reactions.
Look for these in your work
- Two sources.
- Two functions.
A student says only plain drinking water counts as a water source. Evaluate.
Give me a hint
Foods and other drinks contain water.
Compare my reasoning
- Identify water in soup or fruit.
- Separate source type from water molecules.
The claim is false; foods and other drinks can also supply water.
Look for these in your work
- One food example.
- Correct source distinction.
After sweating, a learner says cooling occurs because water becomes glucose. Correct the mechanism.
Give me a hint
Think of a physical change at the skin.
Compare my reasoning
- Sweat water evaporates.
- Evaporation transfers energy away.
- No glucose synthesis is involved.
Evaporation of sweat contributes to cooling; water does not become glucose.
Look for these in your work
- Evaporation mechanism.
- No invented chemical conversion.
Common mistakes
- Water is not a caloric fuel.
- A universal intake target is not given by this syllabus statement.
What can you explain now?
Which is a water function?
Compare with the explanation
A medium for transport and reactions.
These are important body-fluid roles.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain a water role using solvent, solute and transport correctly.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.