Chapter 7: Cellular Respiration

7.1 Energy Production through Cellular Respiration

• Catabolism releases energy; anabolism uses energy (e.g. protein formation). (p.114)
• Cellular respiration is the oxidation of organic molecules in stages to release energy; the main substrate is glucose. (p.114)
• Humans and animals obtain glucose from digested carbohydrates; plants make glucose by photosynthesis. (p.114)
• Types: aerobic (with oxygen) and anaerobic (without oxygen); fermentation is an alternative pathway with incomplete glucose breakdown. (p.114)

7.2 Aerobic Respiration

• Glycolysis occurs in the cytoplasm: one glucose is broken down into two pyruvate molecules. (p.115)
• Pyruvate is oxidised in the mitochondrion to carbon dioxide, water and energy; much of the energy makes ATP. (p.115)
• ADP + phosphate + energy → ATP; breaking the weak phosphate link of ATP releases energy. (p.115)
• Word equation: glucose + oxygen → carbon dioxide + water + energy (2898 kJ). (p.115)
• Respirometer experiment: a cockroach in a tube with soda lime; the coloured liquid rises as oxygen is used and CO₂ is absorbed. (p.116)

7.3 Fermentation

• Fermentation is incomplete breakdown of glucose in limited or no oxygen; it differs from aerobic respiration after glycolysis. (p.117)
• Alcohol fermentation: glucose → ethanol + carbon dioxide + energy (210 kJ). (p.118)
• Yeast: ethanol used for beer and wine; CO₂ makes bread dough rise. (p.118)
• Paddy plants in waterlogged soil carry out alcohol fermentation and tolerate ethanol using alcohol dehydrogenase. (p.118)
• Lactic acid fermentation: glucose → lactic acid + energy; in muscle cells during vigorous exercise when oxygen supply is insufficient (oxygen debt). (p.119)
• Only 2 ATP or 150 kJ per glucose; lactic acid build-up causes fatigue and cramps. (p.119)
• Oxygen debt is repaid after exercise when excess oxygen oxidises lactic acid. (p.119)
• Lactobacillus turns lactose into lactic acid, which coagulates casein to make yoghurt. (p.119)
• Yeast fermentation experiment: boiled glucose solution with yeast under paraffin oil; lime water turns cloudy and temperature rises. (p.120)

Aerobic respiration vs fermentation

(p.121)

Aspect	Aerobic respiration	Fermentation
Oxygen	Complete breakdown with oxygen	Incomplete, without or limited oxygen
Location	Cytoplasm and mitochondrion	Cytoplasm
Water	Produced	Not produced
End products	Carbon dioxide and water	Ethanol and CO2, or lactic acid
Energy per glucose	2898 kJ	210 kJ (alcohol) or 150 kJ (lactic acid)

• Similarities: glucose breakdown, ATP production, begin with glycolysis in the cytoplasm, occur in yeast, bacteria, animals and plants. (p.121)