Understanding Cellular Respiration: A Complete IB Biology Guide
Understanding Cellular Respiration: A Complete IB Biology Guide
Cellular respiration is one of the most important topics in IB Biology and frequently appears in exam questions. Let's break it down step by step.
What is Cellular Respiration?
Cellular respiration is the process by which cells break down glucose to release energy in the form of ATP (adenosine triphosphate). The overall equation is:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP
The Three Stages
1. Glycolysis
Glycolysis occurs in the cytoplasm and doesn't require oxygen (anaerobic). Key points:
- Glucose (6C) is broken down into two molecules of pyruvate (3C)
- Net gain of 2 ATP and 2 NADH
- This is the only stage that occurs in both aerobic and anaerobic respiration
2. The Krebs Cycle (Citric Acid Cycle)
The Krebs cycle takes place in the matrix of the mitochondria:
- Pyruvate is first converted to acetyl CoA (releasing CO₂)
- Acetyl CoA enters the cycle and is systematically broken down
- Products per turn: 1 ATP, 3 NADH, 1 FADH₂, 2 CO₂
- The cycle turns twice per glucose molecule
3. Oxidative Phosphorylation
This occurs on the inner mitochondrial membrane (cristae):
- NADH and FADH₂ donate electrons to the electron transport chain
- Electrons pass through protein complexes, releasing energy
- This energy pumps H⁺ ions across the membrane (chemiosmosis)
- H⁺ flows back through ATP synthase, generating most of the ATP
- Oxygen is the final electron acceptor, forming water
- Produces approximately 34 ATP
Total ATP Yield
| Stage | ATP Produced | |-------|-------------| | Glycolysis | 2 ATP | | Krebs Cycle | 2 ATP | | Oxidative Phosphorylation | ~34 ATP | | Total | ~38 ATP |
HL Extension: Chemiosmosis in Detail
For HL students, you need to understand the electron transport chain in greater detail, including the specific complexes involved and the role of proton gradients in ATP synthesis.
Common Exam Questions
- Compare aerobic and anaerobic respiration
- Explain the role of oxygen in cellular respiration
- Describe the relationship between the structure of the mitochondria and its function
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