Compare energy release per glucose molecule
Use a fair denominator for aerobic and anaerobic comparisons.
Section 12.3 · Anaerobic respiration
Exam scope and assessment notes
Core and Extended · Biology 0970, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked; human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0970 has the same subject content as IGCSE 0610, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Recall cell processes, enzymes and the distinction between gas exchange and breathing.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What must be matched for a yield comparison?
What you will learn
- Keep glucose amount equal
- Distinguish yield from rate
Compare energy release per glucose molecule
| Feature | Meaning |
|---|---|
| Basis | Equal glucose amount |
| Aerobic model | 30 invented units per glucose |
| Anaerobic model | 2 invented units per glucose |
| Conclusion | Much lower anaerobic yield; rate is separate |
Keep glucose amount equal
Anaerobic respiration releases much less energy per glucose molecule than aerobic respiration. The denominator matters: compare the same number of glucose molecules, not a large anaerobic sample with a tiny aerobic sample. Both pathways release energy, so much less is not the same as zero.
The syllabus does not require one universal exact numerical energy yield or a fixed ATP count for this comparison. An invented model may use energy units to practise ratios, provided those values are clearly labelled as teaching values rather than biological constants. Actual yield depends on the process and accounting assumptions.
Distinguish yield from rate
Energy per glucose is a yield comparison. Energy released per second is a rate and also depends on how much glucose is processed per second. A lower yield does not, by itself, prove a slower total rate or mean an anaerobic pathway cannot provide useful energy during vigorous activity.
In an explanation, state both the lower anaerobic yield and the equal-glucose basis. If supplied model values are aerobic 30 units and anaerobic 2 units per glucose, the ratio is fifteen to one for those values only. Do not present the teaching units as an official number of ATP molecules, joules or a guaranteed quantity in every cell.
Pause and explain
Which statement matches the syllabus?
Worked example
Using invented yields of 30 and 2 units per glucose, compare equal glucose amounts.
Show the worked solution
- Both values use the same denominator.
- 30 ÷ 2 = 15.
Answer The aerobic model releases fifteen times as much energy per glucose in these invented values.
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.
State the energy comparison between anaerobic and aerobic respiration.
Give me a hint
Include the equal-glucose basis.
Compare my reasoning
- Both release energy.
- Compare release per glucose molecule.
Anaerobic respiration releases much less energy per glucose molecule than aerobic respiration.
Look for these in your work
- Include much less
- Include per glucose molecule
In the invented 30-versus-2-unit model, find release from two glucose molecules in each pathway.
Give me a hint
Multiply each per-glucose value by two.
Compare my reasoning
- Aerobic: 2 × 30 = 60 units.
- Anaerobic: 2 × 2 = 4 units.
Aerobic model: 60 units; anaerobic model: 4 units. These are invented energy units, not fixed ATP yields.
Look for these in your work
- Match glucose amount
- Retain the model qualification
Does a lower energy yield per glucose alone prove a lower energy-release rate per second?
Give me a hint
Rate also depends on throughput.
Compare my reasoning
- Yield is energy per glucose.
- Rate needs glucose processed per time as well.
No. Per-second release also depends on glucose processed per second; yield alone does not determine rate.
Look for these in your work
- Distinguish yield and rate
- Name the missing throughput
Common mistakes
- Omitting per glucose.
- Turning invented energy units into real ATP yields.
What can you explain now?
Which statement matches the syllabus?
Compare with the explanation
Anaerobic respiration releases much less energy per glucose molecule
It still releases some energy.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
State the equal-glucose comparison and distinguish yield from rate.
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.