Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

2.6Structure & Functions in Living Organisms

Respiration — Edexcel International GCSE Biology 4BI1 Revision Notes & Topical Questions

10 min read 8 parts Lesson 6 of 21 1 quiz

📚 Edexcel International GCSE Biology 4BI1 Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
Curriculum Equation Key Balanced Cellular Respiration EquationFast Exam Solution
C₆H₁₂O₆ + 6O₂ ➔ 6CO₂ + 6H₂O + 36-38 ATP
Word Equation & Conditions: Glucose + Oxygen -> Carbon Dioxide + Water + Energy (36-38 ATP)
0%read
Lesson summary

Respiration Edexcel IGCSE Biology 4BI1 notes: Describe respiration as a process in all living cells releasing energy.Aerobicglucose + oxygen → carbon dioxide + water (+ energy).C6H12O6 + 6O2 → 6CO2 + 6H2OAnaerobic in animalsglucose → lactic acid.Anaerobic in yeast and plantsgluco…

  • Respiration is a chemical reaction carried out in all living cells
  • Aerobic respiration
  • Why aerobic releases more energy
  • Practical – CO2 production
  • Practical – heat production
  • Practical – rate and temperature

Part 1 of 8Key ideas

1Aerobic
Aerobic glucose + oxygen → carbon dioxide + water (+ energy).
2
C6H12O6 + 6O2 → 6CO2 + 6H2O
3Anaerobic in animals
Anaerobic in animals glucose → lactic acid.
4Anaerobic in yeast and plants
Anaerobic in yeast and plants glucose → ethanol + carbon dioxide.
5
Energy from respiration is used for muscle contraction, active transport, protein synthesis, cell division and keeping warm.
6
Limewater turns cloudy (milky) with carbon dioxide.
7
Germinating seeds release heat; a vacuum flask with thermometer shows a temperature rise compared with boiled (dead) seeds.
8
Respiration is controlled by enzymes, so its rate is affected by temperature.

Part 2 of 8Learning objectives

1
Describe respiration as a process in all living cells releasing energy.
2
Write word and balanced symbol equations for aerobic respiration.
3
Compare aerobic and anaerobic respiration in animals and plants/yeast.
4
Describe experiments to investigate the production of CO2 and heat by respiration.

Part 3 of 8Essential knowledge

1Respiration is a chemical reaction carried out in all living cells
Respiration is a chemical reaction carried out in all living cells to release energy from food molecules such as glucose. It is not the same as breathing. Energy is used to make ATP, which provides energy for processes such as muscle contraction, active transport, making large molecules, cell division and maintaining body temperature.
2Aerobic respiration
Aerobic respiration uses oxygen and mostly takes place in mitochondria. Glucose is completely broken down: C6H12O6 + 6O2 → 6CO2 + 6H2O. It releases a large amount of energy.
3Anaerobic respiration in animals
Anaerobic respiration in animals during vigorous exercise muscles may not get enough oxygen, so glucose is converted to lactic acid, releasing less energy. Lactic acid builds up and causes muscle fatigue; after exercise extra oxygen is needed to break it down (oxygen debt), so breathing stays fast.
4Anaerobic respiration in yeast and plants
Anaerobic respiration in yeast and plants glucose → ethanol + carbon dioxide. This is used in bread-making (CO2 makes dough rise) and brewing (ethanol). Plant roots in waterlogged soil may respire anaerobically.
5Why aerobic releases more energy
Why aerobic releases more energy in anaerobic respiration glucose is only partly broken down, so much energy remains in lactic acid or ethanol.
6Practical – CO2 production
Practical – CO2 production air is drawn through limewater or hydrogencarbonate indicator past a small animal or germinating seeds; the indicator changes (limewater cloudy; hydrogencarbonate indicator red → yellow). A control with no organisms shows no change.
7Practical – heat production
Practical – heat production place germinating peas in one vacuum flask and boiled, cooled peas (killed) in another, both washed in disinfectant to stop microbial respiration. Thermometers show a temperature rise only in the live peas.
8Practical – rate and temperature
Practical – rate and temperature a respirometer with soda lime measures oxygen uptake by the movement of a liquid bead. Rate increases with temperature up to an optimum, as respiration is controlled by enzymes, and falls at high temperatures as enzymes denature.
9Lactic acid and muscle pH
Lactic acid lowers the pH of muscle tissue, which can reduce enzyme activity and contributes to fatigue. Later, oxygen is used to break the lactic acid down to carbon dioxide and water.
10Heat practical — controls
Use the same type and mass of seeds in both flasks and rinse them in dilute disinfectant so microbes cannot respire. Plug the flasks with cotton wool to reduce heat loss while allowing air in, and record room temperature to check it stayed constant.

Part 4 of 8Process & sequence

    • Set up a respirometer with germinating seeds (or small invertebrates) in a tube with soda lime.
    • Set up a control tube with glass beads of equal volume instead of organisms.
    • Place tubes in a water bath at a set temperature and allow to equilibrate.
    • Soda lime absorbs CO2, so oxygen uptake reduces the gas volume.
    • The coloured liquid in the capillary tube moves towards the organisms; measure distance in a set time.
    • Repeat at different temperatures and calculate rate (distance ÷ time).

    Measuring respirationwrite these steps in this order; each step is a marking point.

    1. Seeds in tube with soda lime
    2. Control with glass beads
    3. Equilibrate in water bath
    4. O2 absorbed, liquid moves
    5. Measure distance in time
    6. Calculate rate

Part 5 of 8Worked examples

13 mm per minute
In a respirometer, the liquid moved 24 mm in 8 minutes at 20 °C. Calculate the rate of oxygen uptake in mm per minute and explain why soda lime is needed.
  • Rate = 24 ÷ 8 = 3 mm per minute.
    • Soda lime absorbs the carbon dioxide released, so any change in volume is due only to oxygen being taken in by the organisms.
2Explain why an athlete continues to breathe deeply after a sprint.
  • During the sprint the muscles respired anaerobically, producing lactic acid.
    • After exercise extra oxygen is needed to break down the lactic acid (repaying the oxygen debt), so breathing rate and depth remain high.

Part 6 of 8Summary

    • Respiration releases energy from glucose in all cells.
    • Aerobic respiration uses oxygen and releases the most energy.
    • Anaerobic in muscles makes lactic acid; in yeast makes ethanol + CO2.
    • Energy is transferred to ATP for cell processes.
    • Respiration rate can be measured with a respirometer.

Part 7 of 8Keep going

  1. Respiration Edexcel IGCSE Biology 4BI1: what to do next

    These Respiration Edexcel IGCSE Biology 4BI1 notes covered the key ideas, worked examples and exam technique for this topic. Check your Respiration Edexcel IGCSE Biology 4BI1 understanding with the practice questions below, then reread any Respiration Edexcel IGCSE Biology 4BI1 point you were unsure about before moving on.

    Respiration Edexcel IGCSE Biology 4BI1: revision checklist

    • Revise the main Respiration Edexcel IGCSE Biology 4BI1 definitions until you can write them from memory.
    • Practise Respiration Edexcel IGCSE Biology 4BI1 exam questions under timed conditions.

Part 8 of 8Compare: Compare

Aerobic vs anaerobic respiration
FeatureAerobicAnaerobic (animals)Anaerobic (yeast/plants)
Oxygen neededYesNoNo
ProductsCO2 + waterLactic acidEthanol + CO2
Energy releasedLarge amountSmall amountSmall amount
LocationCytoplasm and mitochondriaCytoplasmCytoplasm
Glucose breakdownCompleteIncompleteIncomplete

Key terms

Command terms

Command terms
Give / State / Name
Recall a fact; one idea per mark.
Define
Give the exact meaning using the specification keywords.
Describe
Give an account of what happens / the pattern in data, quoting values; no reasons needed.
Explain
Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.
Suggest
Use knowledge in a new context; more than one answer may be accepted.
Compare
Similarities and differences; each point must refer to both items.
Calculate
Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.
Discuss
Explore the issue from different angles and link the points.
Evaluate / Assess
Weigh strengths and weaknesses and reach a supported judgement.
Deduce
Draw a conclusion from the information given.
Justify
Support a statement/choice with evidence.

Exam technique

Keywords the mark scheme looks for in this lesson

Keywords the mark scheme looks for in this lesson
Respiration · Aerobic respiration · Anaerobic respiration · ATP · Mitochondria · Lactic acid · Oxygen debt · Fermentation · Respirometer
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.

How to get full marks (examiner guidance)

How to get full marks (examiner guidance)
Use specification keywords exactly (e.g. eukaryotic/prokaryotic, enzyme–substrate complex, active site, complementary).
Link ideas
Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.
Use the information in the question
“discuss/evaluate” answers must use the data provided and match the number of marks.
Convert units carefully (mg → g, cm3 → dm3) and show working for calculations.
Avoid vague words
“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.
Do not extrapolate a graph line beyond the data or to zero unless asked.
Six-mark extended responses are marked on content AND a logical, linked line of reasoning.

Last updated:

\n