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7.1.1Unit 5: Respiration, Internal Environment, Coordination and Gene Technology

Overview of Respiration — IAL Edexcel Linear Revision Notes & Topical Questions

5 min read 5 parts Lesson 34 of 36 Unit quiz

📚 IAL Edexcel Linear Hub / Topical Revision
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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)
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Part 1 of 5Aerobic Respiration

7.1.1 Overview of Respiration
Purpose
  • Respiration breaks down respiratory substrates, mainly glucose, to release energy that is used to make ATP.
Equation
  • C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, with the energy released used to make ATP from ADP and phosphate.
Other substrates
  • Fatty acids and amino acids can also be respired when glucose is in short supply.
Enzyme control
  • Each step is catalysed by an enzyme, which releases the energy gradually and avoids overheating that would denature enzymes.

Part 2 of 5The Four Stages

1
Glycolysis takes place in the cytoplasm and does not need oxygen.
2
The link reaction occurs in the matrix of the mitochondrion.
3
The Krebs cycle also occurs in the mitochondrial matrix.
4
Oxidative phosphorylation takes place at the inner membrane of the mitochondrion.
5
Be exact: state the matrix or inner membrane, not just that something happens in the mitochondria.

Part 3 of 5Structure of the Mitochondrion

Structure of the Mitochondrion
Outer membrane
  • This is smooth and permeable to small molecules.
Inner membrane
  • This is folded into cristae, is less permeable, and holds the electron transport chain and ATP synthase.
Intermembrane space
  • Protons pumped here make the space acidic, producing a gradient across the inner membrane.
Matrix
  • This fluid contains enzymes, ribosomes and circular DNA needed for the Krebs cycle and link reaction.

Part 4 of 5Coenzymes

Coenzymes are molecules that help enzymes by carrying chemical groups between reactions.

NAD
  • NAD accepts hydrogen to become reduced NAD, and so carries hydrogen to the electron transport chain.
FAD
  • FAD does the same job, becoming reduced FAD, and also delivers hydrogen to oxidative phosphorylation.
Coenzyme A
  • Coenzyme A carries the acetate group that links the link reaction to the Krebs cycle.
Redox
  • When a coenzyme gains hydrogen it is reduced, and when it loses hydrogen it is oxidised.
StageSiteNeeds oxygen directly?
GlycolysisCytoplasmNo
Link reactionMitochondrial matrixNo
Krebs cycleMitochondrial matrixNo
Oxidative phosphorylationInner membraneYes, as final electron acceptor

Part 5 of 5Exam Checklist & Tips

7.1.1 – Key Points for the Exam

  • Respiratory substrate A molecule such as glucose that is broken down in respiration to release energy.
  • Coenzyme A non-protein molecule that carries atoms or groups between reactions.
  • Cristae The folds of the inner mitochondrial membrane.
  • Phosphorylation Addition of a phosphate group, for example to ADP to form ATP.

Common Mistakes

  • Saying the Krebs cycle takes place in the mitochondria, rather than in the matrix.
  • Writing that respiration makes energy, when it releases energy from the bonds of the substrate to make ATP.
  • Mixing up reduced and oxidised coenzymesgaining hydrogen means reduction.
  • Thinking that glycolysis needs oxygen, when it does not.

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