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
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.
Section 1 of 5Aerobic Respiration
Purpose
- Purpose Respiration breaks down respiratory substrates, mainly glucose, to release energy that is used to make ATP.
Equation
- Equation C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, with the energy released used to make ATP from ADP and phosphate.
Other substrates
- Other substrates Fatty acids and amino acids can also be respired when glucose is in short supply.
Enzyme control
- Enzyme control Each step is catalysed by an enzyme, which releases the energy gradually and avoids overheating that would denature enzymes.
Section 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.
Section 3 of 5Structure of the Mitochondrion
Structure of the Mitochondrion
Outer membrane
- Outer membrane This is smooth and permeable to small molecules.
Inner membrane
- Inner membrane This is folded into cristae, is less permeable, and holds the electron transport chain and ATP synthase.
Intermembrane space
- Intermembrane space Protons pumped here make the space acidic, producing a gradient across the inner membrane.
Matrix
- Matrix This fluid contains enzymes, ribosomes and circular DNA needed for the Krebs cycle and link reaction.
Section 4 of 5Coenzymes
Coenzymes are molecules that help enzymes by carrying chemical groups between reactions.
NAD
- NAD NAD accepts hydrogen to become reduced NAD, and so carries hydrogen to the electron transport chain.
FAD
- FAD FAD does the same job, becoming reduced FAD, and also delivers hydrogen to oxidative phosphorylation.
Coenzyme A
- Coenzyme A Coenzyme A carries the acetate group that links the link reaction to the Krebs cycle.
Redox
- Redox When a coenzyme gains hydrogen it is reduced, and when it loses hydrogen it is oxidised.
| Stage | Site | Needs oxygen directly? |
|---|---|---|
| Glycolysis | Cytoplasm | No |
| Link reaction | Mitochondrial matrix | No |
| Krebs cycle | Mitochondrial matrix | No |
| Oxidative phosphorylation | Inner membrane | Yes, as final electron acceptor |
Section 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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