BIO101 – Topic 27: Respiration and Energy Release in Living
Organisms
27.1 Introduction
All living organisms require energy to perform vital life processes such as growth, movement, repair,
and reproduction. This energy is obtained through respiration, a process that breaks down food
molecules to release usable energy in the form of ATP (adenosine triphosphate). Respiration is
essential for maintaining life and enabling various metabolic activities.
27.2 Definition of Respiration
Respiration is the biochemical process by which cells break down glucose and other organic molecules
to release energy, which is stored in ATP. It involves a series of enzyme-controlled reactions occurring
within the cell.
27.3 Types of Respiration (Aerobic & Anaerobic)
1. **Aerobic Respiration** - Requires oxygen. - Glucose is completely broken down into carbon dioxide
and water. - Produces a large amount of energy (about 36–38 ATP per glucose molecule). Equation:
C■H■■O■ + 6O■ → 6CO■ + 6H■O + Energy (ATP) 2. **Anaerobic Respiration** - Occurs without
oxygen. - Incomplete breakdown of glucose. - Produces less energy (2 ATP per glucose molecule).
Example in animals: C■H■■O■ → 2C■H■O■ + Energy (Glucose → Lactic acid + Energy) Example in
yeast: C■H■■O■ → 2C■H■OH + 2CO■ + Energy (Glucose → Ethanol + Carbon dioxide + Energy)
27.4 Raw Materials and End Products
Raw Materials: - Glucose (C■H■■O■) - Oxygen (O■) — in aerobic respiration End Products: - Carbon
dioxide (CO■) - Water (H■O) - Energy (ATP) - In anaerobic respiration: lactic acid or ethanol and
carbon dioxide
27.5 Stages of Respiration
1. **Glycolysis** - Occurs in the cytoplasm. - Glucose is broken down into two molecules of pyruvate. -
Produces 2 ATP and 2 NADH. 2. **Krebs Cycle (Citric Acid Cycle)** - Occurs in the mitochondrial
matrix. - Pyruvate is oxidized to produce CO■, NADH, FADH■, and 2 ATP. 3. **Electron Transport
Chain (ETC)** - Occurs on the inner mitochondrial membrane. - Uses NADH and FADH■ to generate
ATP through oxidative phosphorylation. - Produces most of the ATP (about 34 ATP molecules).
27.6 Energy Yield (ATP Production)
- **Aerobic Respiration:** 36–38 ATP molecules per glucose molecule. - **Anaerobic Respiration:** 2
ATP molecules per glucose molecule.
27.7 Comparison between Photosynthesis and Respiration
| Feature | Photosynthesis | Respiration | |----------|----------------|--------------| | Occurs in | Chloroplasts |
Mitochondria | | Energy | Stored (light → chemical) | Released (chemical → usable) | | Raw Materials |
CO■ and H■O | Glucose and O■ | | Products | Glucose and O■ | CO■ and H■O | | Type of Process |
Anabolic (building up) | Catabolic (breaking down) |
Organisms
27.1 Introduction
All living organisms require energy to perform vital life processes such as growth, movement, repair,
and reproduction. This energy is obtained through respiration, a process that breaks down food
molecules to release usable energy in the form of ATP (adenosine triphosphate). Respiration is
essential for maintaining life and enabling various metabolic activities.
27.2 Definition of Respiration
Respiration is the biochemical process by which cells break down glucose and other organic molecules
to release energy, which is stored in ATP. It involves a series of enzyme-controlled reactions occurring
within the cell.
27.3 Types of Respiration (Aerobic & Anaerobic)
1. **Aerobic Respiration** - Requires oxygen. - Glucose is completely broken down into carbon dioxide
and water. - Produces a large amount of energy (about 36–38 ATP per glucose molecule). Equation:
C■H■■O■ + 6O■ → 6CO■ + 6H■O + Energy (ATP) 2. **Anaerobic Respiration** - Occurs without
oxygen. - Incomplete breakdown of glucose. - Produces less energy (2 ATP per glucose molecule).
Example in animals: C■H■■O■ → 2C■H■O■ + Energy (Glucose → Lactic acid + Energy) Example in
yeast: C■H■■O■ → 2C■H■OH + 2CO■ + Energy (Glucose → Ethanol + Carbon dioxide + Energy)
27.4 Raw Materials and End Products
Raw Materials: - Glucose (C■H■■O■) - Oxygen (O■) — in aerobic respiration End Products: - Carbon
dioxide (CO■) - Water (H■O) - Energy (ATP) - In anaerobic respiration: lactic acid or ethanol and
carbon dioxide
27.5 Stages of Respiration
1. **Glycolysis** - Occurs in the cytoplasm. - Glucose is broken down into two molecules of pyruvate. -
Produces 2 ATP and 2 NADH. 2. **Krebs Cycle (Citric Acid Cycle)** - Occurs in the mitochondrial
matrix. - Pyruvate is oxidized to produce CO■, NADH, FADH■, and 2 ATP. 3. **Electron Transport
Chain (ETC)** - Occurs on the inner mitochondrial membrane. - Uses NADH and FADH■ to generate
ATP through oxidative phosphorylation. - Produces most of the ATP (about 34 ATP molecules).
27.6 Energy Yield (ATP Production)
- **Aerobic Respiration:** 36–38 ATP molecules per glucose molecule. - **Anaerobic Respiration:** 2
ATP molecules per glucose molecule.
27.7 Comparison between Photosynthesis and Respiration
| Feature | Photosynthesis | Respiration | |----------|----------------|--------------| | Occurs in | Chloroplasts |
Mitochondria | | Energy | Stored (light → chemical) | Released (chemical → usable) | | Raw Materials |
CO■ and H■O | Glucose and O■ | | Products | Glucose and O■ | CO■ and H■O | | Type of Process |
Anabolic (building up) | Catabolic (breaking down) |
