Revision notes · Bioenergetics
Respiration
Aerobic and anaerobic respiration4.4.2.1
Definition: Cellular respiration is an exothermic reaction that continuously occurs in living cells to release energy from glucose.
Cells break down glucose to release energy either with or without oxygen.
| Aerobic | Anaerobic (animals) | Anaerobic (plant/yeast) | |
|---|---|---|---|
| Oxygen needed? | Yes | No | No |
| Products | Carbon dioxide + water | Lactic acid | Ethanol + carbon dioxide (fermentation) |
| Energy released | A large amount | Much less than aerobic | Much less than aerobic |
- •The word equation for aerobic respiration is glucose + oxygen → carbon dioxide + water.
⚠️ Common mistake: Thinking that respiration is the same physical process as breathing or ventilation.
🧠 Remember: Aerobic uses Air (oxygen); Anaerobic means Absent oxygen.
Response to exercise4.4.2.2
Definition: Oxygen debt is the amount of extra oxygen required after exercise to react with accumulated lactic acid and remove it from cells.
During exercise, the body adjusts to supply more oxygen and glucose to working muscles.
- •During exercise, heart rate, breathing rate, and breath volume increase to supply muscles with more oxygenated blood.
- •If the oxygen supply is insufficient, muscles switch to anaerobic respiration, causing a build-up of lactic acid.
- •Accumulation of lactic acid causes muscle fatigue, preventing muscles from contracting efficiently.
- •Blood transports lactic acid from muscles to the liver, where oxygen breaks it down or converts it back into glucose.
⚠️ Common mistake: Thinking lactic acid is removed by breathing it out rather than being processed in the liver.
🧠 Remember: Oxygen debt is paid back after exercise to clear lactic acid in the liver.
Metabolism4.4.2.3
Definition: Metabolism is the sum of all the chemical reactions that take place inside a cell or the body.
Energy transferred by respiration powers all the chemical processes that build up or break down molecules in the body.
- •All metabolic reactions are controlled by enzymes and powered by energy released from respiration.
- •Synthesis reactions convert glucose into starch, glycogen, and cellulose, and combine glycerol and fatty acids to form lipids.
- •Glucose combined with nitrate ions forms amino acids, which are synthesised into proteins.
- •Breakdown reactions include respiration and the breakdown of excess proteins into urea for excretion.
⚠️ Common mistake: Thinking metabolism only refers to digestion or how fast someone burns food.
🧠 Remember: Metabolism = ALL chemical reactions (Making and Breaking molecules).
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