Connect carbohydrate sources with energy supply
Name common carbohydrate sources and their role in respiration.
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
Which is a large carbohydrate?
What you will learn
- Name common carbohydrate sources and their role in respiration.
- Distinguish a food source from an absorbed nutrient molecule.
A source is not a molecule
| Component | Examples of sources | Role |
|---|---|---|
| Carbohydrate | Rice, bread, potatoes | Energy source for respiration |
Recognise sources
Rice, bread, pasta, potatoes and other cereal or starchy foods are important carbohydrate sources. Sugars in fruit and other foods also contribute carbohydrate. Wholegrain sources can supply fibre as well; the categories overlap within foods.
Starch is a large carbohydrate that must be digested before its building blocks are absorbed. A source food is not the same thing as a molecule: rice contains more than pure starch.
Connect food with cells
Absorbed glucose can be used in respiration to release energy for cell activities. Eating carbohydrate and releasing energy by respiration are separate stages; energy is not created when a food enters the mouth.
Do not call carbohydrate the only energy source. Fats and other nutrients can also supply chemical energy, but carbohydrate is an important readily used source in this syllabus.
Sources for this lesson
Pause and explain
Which source-function pair fits carbohydrate?
Worked example
A question names bread and glucose uptake by muscle cells. Connect the food source to the cellular function.
Show the worked solution
- Bread supplies starch.
- Digestion makes small soluble sugars available.
- Cells can use glucose in respiration.
Answer Carbohydrate from bread can supply glucose for energy release by respiration.
Try a topic test
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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.
Give two principal dietary carbohydrate sources and their main function.
Give me a hint
Use starchy foods.
Compare my reasoning
- Choose rice and potatoes.
- Connect carbohydrate to respiration.
Rice and potatoes; carbohydrate supplies an energy source for respiration.
Look for these in your work
- Two suitable sources.
- Energy function.
Why is “bread contains starch” more accurate than “bread is one starch molecule”?
Give me a hint
Separate food and molecule.
Compare my reasoning
- Bread is a mixture.
- Starch molecules form one component.
Bread is a food mixture containing many starch molecules and other components.
Look for these in your work
- Mixture distinction.
- Correct carbohydrate identification.
A learner says starch is absorbed unchanged and then chewed by muscle cells. Correct both stages.
Give me a hint
Place digestion before absorption.
Compare my reasoning
- Starch is digested to small soluble sugars.
- These are absorbed.
- Glucose can be respired by cells.
Starch is digested in the digestive system; absorbed sugars can supply cells for respiration.
Look for these in your work
- No intact starch uptake claim.
- Cell respiration rather than chewing.
Common mistakes
- Food sources contain mixtures.
- Respiration occurs in cells, not as a synonym for chewing.
What can you explain now?
Which source-function pair fits carbohydrate?
Compare with the explanation
Rice: an energy source for respiration.
Rice supplies substantial starch.
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Make it stick
Trace a starchy source to a cellular energy function.
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.