Overview
This lecture covers the key concepts of bioenergetics in Biology Paper 1, focusing on photosynthesis, respiration, metabolism, and comparisons between aerobic and anaerobic respiration.
Photosynthesis
- Photosynthesis converts carbon dioxide and water into glucose and oxygen using light energy.
- Word equation: carbon dioxide + water → (light) → glucose + oxygen.
- Balanced symbol equation: 6CO₂ + 6H₂O → (light) → C₆H₁₂O₆ + 6O₂.
- Plants use glucose for respiration, building cellulose, making amino acids, storing as fats/oils, and storing as starch.
- The rate of photosynthesis is limited by factors such as light, temperature, and carbon dioxide concentration.
- Graphs show that increasing CO₂ raises the rate of photosynthesis up to a point, after which another factor becomes limiting.
- Industrial greenhouses use controlled conditions (light, heat, CO₂) for optimal photosynthesis; paraffin heaters add CO₂.
- High temperatures can denature enzymes, stopping photosynthesis.
Respiration
- Respiration releases energy by breaking down glucose with oxygen, producing carbon dioxide and water.
- Word equation: glucose + oxygen → carbon dioxide + water.
- Balanced symbol equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O.
- Energy from respiration is used to build larger molecules, contract muscles, and maintain constant body temperature.
Metabolism
- Metabolism is all the chemical reactions in an organism.
- Includes synthesis (building molecules) and decomposition (breaking down molecules) reactions.
- Examples: making starch from glucose, proteins from amino acids, and breaking down glucose in respiration.
Aerobic vs Anaerobic Respiration
- Aerobic respiration uses oxygen and produces carbon dioxide and water.
- Anaerobic respiration occurs without oxygen, converting glucose to lactic acid in animals.
- Anaerobic respiration leads to an oxygen debt, which is repaid by heavy breathing after intense activity to remove lactic acid.
Key Terms & Definitions
- Photosynthesis — process by which plants convert CO₂ and water into glucose and O₂ using light.
- Limiting Factor — an environmental factor that restricts the rate of a process (like photosynthesis).
- Respiration — process of releasing energy from glucose.
- Metabolism — sum of all chemical reactions in an organism.
- Aerobic Respiration — respiration using oxygen.
- Anaerobic Respiration — respiration without oxygen, producing lactic acid.
Action Items / Next Steps
- Memorize both the word and balanced symbol equations for photosynthesis and respiration.
- Practice analyzing rate of photosynthesis graphs.
- Be familiar with definitions of key terms.