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Cambridge IGCSE Biology 0610: Respiration Notes (Aerobic and Anaerobic)
Respiration is the set of chemical reactions in cells that break down nutrient molecules, such as glucose, to release energy. These notes cover respiration for the Cambridge IGCSE Biology (0610) syllabus: uses of energy, aerobic respiration, anaerobic respiration in muscles and yeast, oxygen debt, and respiration investigations, with a sorting exercise, a yeast simulation, calculators, a quiz, worked examples and exam tips.
Try the yeast simulationBook a 1-to-1 lessonWritten by Ms. Humaira Asim, a science teacher with 15+ years of teaching experience. Written for the Cambridge IGCSE Biology 0610 syllabus.
What is respiration?
Respiration is the chemical reactions in cells that break down nutrient molecules (mainly glucose) and release energy. It happens in every living cell, all the time, in plants as well as animals.
Respiration is not the same as breathing. Breathing moves air in and out of the lungs. Respiration is a chemical process inside cells.
The reactions of respiration are controlled by enzymes, so temperature affects the rate. The rate rises up to the optimum temperature, then falls as the enzymes are denatured.
Uses of energy
Living things use the energy released by respiration for:
- muscle contraction
- protein synthesis (making proteins)
- cell division
- active transport
- growth
- the passage of nerve impulses
- keeping a constant body temperature (in mammals and birds)
Aerobic respiration
Aerobic respiration uses oxygen. It releases a lot of energy from each glucose molecule. Most of it happens in the mitochondria.
Anaerobic respiration
Anaerobic respiration happens without oxygen. It releases much less energy from each glucose molecule, because the glucose is only partly broken down.
In muscles (during hard exercise)
In yeast (fermentation)
Anaerobic respiration in yeast is used in bread-making, where the carbon dioxide makes the dough rise, and in brewing, to make alcohol.
Aerobic vs anaerobic respiration
| Aerobic | Anaerobic | |
|---|---|---|
| Needs oxygen? | Yes | No |
| Energy released per glucose | Large amount | Much less |
| Products | Carbon dioxide and water | Lactic acid (muscles), or alcohol and carbon dioxide (yeast) |
| Where in the cell | Mostly in the mitochondria | In the cytoplasm |
Sorting exercise
Aerobic, anaerobic or both?
Choose an answer for each statement, then press Check my answers.
Oxygen debt (Extended)
During hard exercise, muscles cannot get oxygen fast enough, so they also respire anaerobically and lactic acid builds up. This causes muscle fatigue.
- After exercise, extra oxygen is needed to break down the lactic acid. This is the oxygen debt.
- Lactic acid is carried in the blood to the liver, where it is broken down by aerobic respiration.
- This is why your heart rate and breathing rate stay high for a while after exercise.
Investigating respiration
Using a respirometer
- Put germinating seeds (or small animals, such as woodlice) on gauze above soda lime in a sealed tube.
- The soda lime absorbs the carbon dioxide they breathe out.
- As the seeds use oxygen, the volume of gas in the tube falls, so the coloured drop moves towards the seeds.
- Measure how far the drop moves in a set time. A faster drop means a faster rate of respiration.
- Use a control tube with boiled (dead) seeds or glass beads, so you know any movement is caused by respiration.
Yeast and temperature
Yeast in sugar solution respires and gives off carbon dioxide. You can count the bubbles, or see the limewater turn milky, which shows carbon dioxide is present. Repeat at different temperatures using a water bath.
Try it: yeast and temperature
Yeast respires sugar and gives off carbon dioxide bubbles. Change the temperature of the water bath and watch the rate change.
These numbers come from a simple model to show the pattern, not real results.
Worked examples
Example 1: respirometer rate
In a respirometer, the drop moves 24 mm in 8 minutes. Calculate the rate of respiration.
- rate = distance ÷ time = 24 ÷ 8
- = 3 mm per minute
Example 2: volume of oxygen used
The capillary tube has a radius of 0.5 mm and the drop moves 24 mm. Calculate the volume of oxygen used.
- volume = πr² × distance = 3.14 × 0.5² × 24
- = 3.14 × 0.25 × 24
- ≈ 18.8 mm³
Example 3: explaining a result
The drop in a respirometer with boiled seeds does not move. Explain why.
- Boiled seeds are dead, so they do not respire
- No oxygen is used, so the volume of gas stays the same
- This shows that the movement in the other tube was caused by respiration
Example 4: checking the balanced equation (Extended)
Show that C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O is balanced.
- Left: C = 6, H = 12, O = 6 + 12 = 18
- Right: C = 6, H = 12, O = 12 + 6 = 18
- Same number of each atom on both sides, so it is balanced
Try it yourself: respiration calculators
Respirometer rate
rate = distance ÷ time
Volume of oxygen used
volume = π × r² × distance
Quick quiz
Quick quiz: respiration
Choose an answer for each question. You get feedback straight away.
1. What is the word equation for aerobic respiration?
2. Where does aerobic respiration happen in a cell?
3. What do human muscles make during anaerobic respiration?
4. What does yeast make during anaerobic respiration?
5. Which type of respiration releases more energy from each glucose molecule?
6. Which of these is NOT a use of energy from respiration?
7. Why does the rate of respiration fall at very high temperatures?
8. Why do you keep breathing fast after exercise? (Extended)
Common mistakes
- Saying respiration “makes” energy. Energy cannot be made. Respiration releases energy from glucose.
- Mixing up respiration and breathing. Breathing is moving air; respiration is a chemical reaction in cells.
- Saying plants only photosynthesise. Plants respire all the time, day and night.
- Adding carbon dioxide to anaerobic respiration in muscles. Muscles make only lactic acid.
- Forgetting the control in respirometer experiments.
Practice questions
Try each question first, then open it to check your answer.
Q1. Define respiration.
The chemical reactions in cells that break down nutrient molecules and release energy.
Q2. Give three uses of energy in the human body.
Any three: muscle contraction, protein synthesis, cell division, active transport, growth, nerve impulses, keeping a constant body temperature.
Q3. State the word equation for anaerobic respiration in yeast.
glucose → alcohol + carbon dioxide
Q4. Why does anaerobic respiration release less energy than aerobic respiration?
Because glucose is only partly broken down; some energy is still stored in the lactic acid or alcohol.
Q5. Why does bread dough rise?
Yeast respires anaerobically and gives off carbon dioxide gas, which makes the dough rise.
Q6. A respirometer drop moves 15 mm in 5 minutes. Calculate the rate.
15 ÷ 5 = 3 mm per minute
Q7. What is the job of soda lime in a respirometer?
It absorbs carbon dioxide, so the change in volume is caused only by oxygen being used.
Q8. Explain why an athlete keeps breathing deeply after a race. (Extended)
Lactic acid built up during anaerobic respiration. Extra oxygen (the oxygen debt) is needed to break down the lactic acid in the liver.
Exam tips
- Always say respiration releases energy; never say it “produces” or “makes” energy.
- Learn the three word equations: aerobic, anaerobic in muscles, and anaerobic in yeast.
- In experiments, mention the control, keeping the temperature the same, and repeating to check results.
- Link temperature effects to enzymes and their optimum temperature.
Frequently asked questions
What is the difference between aerobic and anaerobic respiration?
Aerobic respiration uses oxygen and releases a lot of energy, making carbon dioxide and water. Anaerobic respiration happens without oxygen, releases much less energy, and makes lactic acid in muscles or alcohol and carbon dioxide in yeast.
What is the word equation for aerobic respiration?
Glucose + oxygen → carbon dioxide + water.
Is respiration the same as breathing?
No. Breathing moves air in and out of the lungs. Respiration is the chemical process in cells that releases energy from glucose.
What is oxygen debt?
The extra oxygen needed after exercise to break down the lactic acid made during anaerobic respiration.
Are these notes suitable for KS3 or Year 8 science?
Yes, the word equations and the uses of energy suit Year 7 to 9 (KS3) science. The symbol equations and oxygen debt are GCSE and IGCSE content.
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Book a 1-to-1 lessonTry the Biology calculatorRelated notes: Photosynthesis · Cells and cell structure · Diffusion, osmosis and active transport · Biology notes topic list. This topic is also part of GCSE and IGCSE Combined Science: see all Combined Science notes. These notes follow the Cambridge IGCSE Biology 0610 syllabus. Always check the current syllabus on the Cambridge International website.