2fStructures and Functions in Living Organisms
Respiration — Edexcel Linear - OL Revision Notes & Topical Questions
10 min read 8 parts Lesson 6 of 25 1 quiz
Curriculum Equation Key معادلة التنفس الخلوي الهوائي الموزونة - 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) | جلوكوز + أكسجين ← ثاني أكسيد كربون + ماء + طاقة
Location & Specifications: الميتوكوندريا (Mitochondria) والسيتوسول.
Lesson summary
Respiration Edexcel O Level Linear Biology notes: understand how the process of respiration produces ATP in living organismsRespiration happens in all living cells, all the time.Plants respire as well as photosynthesise.Energy from respiration is used for movement, growth and kee…
- Word equation (aerobic)
- Balanced symbol equation (aerobic)
- Anaerobic in animals
- Anaerobic in plants and yeast
- Heat practical
- Write the balanced symbol equation for aerobic respiration
Part 1 of 7Key ideas
Key ideas
Respiration happens in all living cells, all the time.
Plants respire as well as photosynthesise.
Energy from respiration is used for movement, growth and keeping warm.
Chemical reaction
Respiration is a chemical reaction that releases energy from glucose — it happens in all organisms and in every living cell.
ATP
The energy is released as ATP, and is used for three main things: building larger molecules from smaller ones, muscle contraction (movement), and keeping warm to hold a constant temperature for enzyme activity.
Word equation (aerobic)
Word equation (aerobic) glucose + oxygen → carbon dioxide + water.
Balanced symbol equation (aerobic)
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O.
Anaerobic in animals
Anaerobic in animals glucose → lactic acid.
Anaerobic in plants and yeast
Anaerobic in plants and yeast glucose → ethanol + carbon dioxide.
A lot
Aerobic respiration releases a lot of ATP per glucose; anaerobic respiration releases only a little, because the breakdown of glucose is incomplete.
Controls
Boiled seeds and glass beads are the controls in the limewater practical: neither can respire.
Heat practical
Heat practical two vacuum flasks, A with dead seeds and B with germinating seeds, seeds sterilised with weak bleach, plugged with cotton wool, inverted, temperatures recorded over 2–3 days. Result: B rises about +5.5 °C, A shows 0.0 °C; room temperature is measured for comparison.
Reduce heat loss
Vacuum flasks are used because they reduce heat loss to the surroundings, and the seeds are sterilised so that microorganisms do not respire as well.
Part 2 of 7Syllabus points
1
understand how the process of respiration produces ATP in living organisms
2
know that ATP provides energy for cells
3
describe the differences between aerobic and anaerobic respiration
4
know the word equation and the balanced chemical symbol equation for aerobic respiration in living organisms
5
know the word equation for anaerobic respiration in plants and in animals
6
practical: investigate the evolution of carbon dioxide and heat from respiring seeds or other suitable living organisms
Part 3 of 7Process & sequence
- Glucose
- + Oxygen
- → Carbon dioxide
- + Water
- + Energy
1
Food is digested into glucose.
2
Blood carries glucose and oxygen to cells.
3
Mitochondria respire → energy released.
4
Carbon dioxide travels back to the lungs.
5
It is breathed out.
1
During vigorous exercise the muscles have a high energy demand.
2
Oxygen delivery to the muscle fibres is insufficient for aerobic respiration.
3
Glucose is therefore broken down anaerobically, giving a small amount of ATP.
4
Lactic acid builds up in the muscle.
5
The pH falls and becomes acidic, so enzymes can no longer work at their optimum.
6
The lactic acid is broken down later, using oxygen, to carbon dioxide and water.
Aerobic respiration in the bodywrite these steps in this order; each step is a marking point.
1
Food is digested to glucose
2
Blood carries glucose to the cells
3
Oxygen is breathed in and carried to the cells
4
Glucose and oxygen enter the mitochondria
5
Energy is released as ATP
6
Carbon dioxide diffuses into the blood
7
Carbon dioxide is breathed out
Anaerobic respiration during vigorous exerciseorder these.
1
Muscles need more energy
2
Oxygen supply is insufficient
3
Glucose is broken down anaerobically
4
Lactic acid forms and the pH falls
5
Enzymes denature in the acidic conditions
6
Lactic acid is later broken down using oxygen
Part 4 of 7Worked examples
1Write the balanced symbol equation for aerobic respiration.
- C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O. Check the atoms balance: 6 carbon on each side, 12 hydrogen, and 6 + 12 = 18 oxygen.
2Cloudy
Tube A contains germinating seeds and tube B boiled seeds, both with limewater. Predict and explain.
- A turns cloudy because the living seeds respire and release carbon dioxide.
- B shows no change because boiling killed the seeds, so no respiration takes place.
- B is the control.
3Reduce heat loss
A student respiring-seed flask warmed by 5.5 °C over three days while the dead-seed flask did not warm. Why use vacuum flasks and why sterilise the seeds?
- Vacuum flasks reduce heat loss, so the temperature rise from respiration can be detected.
- Seeds are sterilised with weak bleach so that microorganisms on the surface do not respire and add heat that is not from the seeds.
4Explain why a runner's muscles fatigue near the end of a race.
- Oxygen cannot be delivered fast enough, so glucose is broken down anaerobically. Lactic acid accumulates, the pH falls, and enzymes stop working at their optimum, so the muscle contracts less effectively.
Part 5 of 7Summary
1
Glucose + oxygen → carbon dioxide + water (+ energy).
2
Respiration happens in the mitochondria.
3
Respiration transfers energy from glucose to ATP in every living cell.
4
ATP is used to build molecules, to contract muscles and to keep warm.
5
Aerobic = oxygen used, complete breakdown, CO₂ + water, lots of ATP; anaerobic = no oxygen, incomplete, lactic acid or ethanol + CO₂, little ATP.
6
During hard exercise muscles respire anaerobically, lactic acid builds up, the pH falls and enzymes denature.
7
Germinating seeds turn limewater cloudy and warm a vacuum flask; dead seeds and beads do neither.
Part 6 of 7Keep going
Respiration Edexcel O Level Linear Biology: what to do next
These Respiration Edexcel O Level Linear Biology notes covered the key ideas, worked examples and exam technique for this topic. Check your Respiration Edexcel O Level Linear Biology understanding with the practice questions below, then reread any Respiration Edexcel O Level Linear Biology point you were unsure about before moving on.
Respiration Edexcel O Level Linear Biology: revision checklist
1
Revise the main Respiration Edexcel O Level Linear Biology definitions until you can write them from memory.
2
Practise Respiration Edexcel O Level Linear Biology exam questions under timed conditions.
3
Link each Respiration Edexcel O Level Linear Biology idea to a diagram or a worked example.
4
List the common Respiration Edexcel O Level Linear Biology mistakes and how to avoid them.
5
Explain one Respiration Edexcel O Level Linear Biology idea out loud as if teaching a friend.
6
Summarise Respiration Edexcel O Level Linear Biology in five key points on a revision card.
2
Previous lesson: 2e Nutrition — Notes
3
Next lesson: 2g Gas exchange — Notes
4
Course: Edexcel Linear - OL — all units
5
Official syllabus: Pearson Edexcel International GCSEs
Part 7 of 7Compare: Compare
| Feature | Breathing | Respiration | Where | Involves | Product |
|---|---|---|---|---|---|
| Type of process | Physical (movement) | Chemical reaction | — | — | — |
| Location | Lungs / chest | Every living cell | Mitochondria | — | — |
| Purpose | Move air in and out | Release energy | — | — | Energy |
| Gases | Moves O₂ in, CO₂ out | Uses O₂, makes CO₂ | — | Oxygen + glucose | CO₂ + water |
| Organisms | Animals with lungs | All living things | Plants too | — | — |
| Feature | Aerobic | Anaerobic |
|---|---|---|
| Oxygen | Used | Not used |
| Breakdown of glucose | Complete | Incomplete |
| Products | Carbon dioxide + water | Lactic acid (animals) or ethanol + carbon dioxide (plants, yeast) |
| Energy released per glucose | A lot | A little |
| Where it happens | Mitochondria | Muscle cells (animals); cytoplasm of yeast/plants |
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 · Glucose · Mitochondria · Energy · Reactant · Product · Word equation · Blood · Anaerobic respiration
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.
Keywords the mark scheme looks for in this lesson
- Respiration — ATP — Aerobic — Anaerobic — Fermentation — Mitochondria — Glucose — Lactic acid — Ethanol — Limewater — CORMS
- Never write "energy is made". Respiration transfers or releases energy as ATP.
Equations
- Learn both forms
- the word equation and the balanced symbol equation, with the 6 in front of O₂ and CO₂.
- Writing only the reactants scores nothing.
- State which product belongs to which pathway: lactic acid is animals;
- ethanol + carbon dioxide is plants and yeast.
Investigation questions
Investigation questions use CORMS
- Change
- what differs between the tubes or flasks.
- (the contents: germinating seeds, boiled seeds, glass beads)
- what differs between the tubes or flasks.
- Organism
- the same type and number of seeds in every tube.
- Repeat
- repeat to obtain reliable results.
- Measure
- the same measurement in each: how long the limewater takes to turn cloudy, or the temperature, measured after the same set time.
- Same
- the controlled variables: number of seeds, temperature, volume of indicator, size of flask.
Comparison questions
- Compare one feature per line (oxygen, completeness of breakdown, products, ATP yield, site).
- Do not describe aerobic respiration in full and then anaerobic in full — the marks are awarded for the pairs.
Marked practiceQuizzes for this lesson
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