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Respiration

邊玩邊學

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課程筆記

Respiration in Cells

  • Respiration is a chemical process that breaks down nutrient molecules (especially glucose) to release energy stored in their bonds.
  • Respiration is enzyme-controlled and occurs in all living cells; most aerobic reactions take place in mitochondria.
  • Respiration can be aerobic (with oxygen) or anaerobic (without oxygen). Aerobic releases much more energy per glucose molecule.
  • Energy released is used for: muscle contraction, protein synthesis, cell division, growth, active transport, nerve impulses, and maintaining body temperature.

Uses of energy released in respiration

Uses of energy released in respiration

Aerobic Respiration

  • Aerobic respiration uses oxygen to completely break down glucose, releasing a relatively large amount of energy.
  • Word equation: glucose + oxygen → carbon dioxide + water
  • Balanced symbol equation (Extended): C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
  • Products are carbon dioxide and water; energy is released for cellular processes.

Word equation for aerobic respiration

Word equation for aerobic respiration

Anaerobic Respiration in Animals

  • Anaerobic respiration does not use oxygen; it is the incomplete breakdown of glucose, releasing less energy.
  • In animals (e.g., during vigorous exercise), glucose is converted to lactic acid.
  • Word equation: glucose → lactic acid
  • Lactic acid build-up lowers pH in muscle cells, which can denature enzymes; it must be removed.

Word equation for anaerobic respiration in animals

Word equation for anaerobic respiration in animals

Anaerobic Respiration in Yeast

  • In yeast, anaerobic respiration produces ethanol and carbon dioxide.
  • Word equation: glucose → ethanol + carbon dioxide
  • Balanced symbol equation (Extended): C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
  • Used in bread-making (CO₂ makes dough rise) and brewing (ethanol gives alcohol, CO₂ gives fizz).

Word equation for anaerobic respiration in yeast

Word equation for anaerobic respiration in yeast

Oxygen Debt (Extended)

  • After exercise, lactic acid is transported to the liver and oxidised (using oxygen) to CO₂ and H₂O.
  • This requires extra oxygen, known as repaying the oxygen debt.
  • Breathing rate and heart rate remain high after exercise to deliver oxygen to the liver for lactic acid oxidation.

Comparing Aerobic and Anaerobic Respiration

  • Aerobic: uses oxygen, complete breakdown, large energy release, products CO₂ + H₂O.
  • Anaerobic (animals): no oxygen, incomplete, small energy release, product lactic acid only.
  • Anaerobic (yeast): no oxygen, incomplete, small energy release, products ethanol + CO₂.
  • Anaerobic respiration in animals does not produce CO₂ – that is a common exam mistake.

Comparing aerobic and anaerobic respiration

Comparing aerobic and anaerobic respirationFeatureAerobicAnaerobic(animals)Anaerobic(yeast)OxygenNeededNot neededNot neededGlucosebreakdownCompleteIncompleteIncompleteProductsCarbondioxide +waterLactic acidonlyEthanol +carbon dioxideEnergyreleasedA lotA littleA little

Effect of Temperature on Respiration (Yeast Experiment)

  • Methylene blue dye is added to a yeast-glucose suspension; it turns from blue to colourless as respiration occurs.
  • The time for colour change measures the rate of respiration (faster change = faster rate).
  • Independent variable: temperature; dependent variable: rate of respiration (time for colour change).
  • Control variables: volume/concentration of dye, yeast, glucose; pH (use buffer).
  • Rate increases up to ~40 °C (more kinetic energy, more enzyme-substrate collisions), then decreases as enzymes denature above optimum temperature.

Methylene blue apparatus

Methylene blue apparatus

投影片

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練習題

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  1. 1.Which of these shows the correct products of aerobic respiration?

    Easy
    • Aenergy, water, carbon dioxide
    • Benergy, lactic acid, carbon dioxide
    • Cenergy, water, lactic acid
    • Dwater, carbon dioxide, lactic acid
  2. 2.What is the correct word equation for aerobic respiration in plants?

    Easy
    • Aglucose + oxygen → carbon dioxide + water
    • Bcarbon dioxide + water → glucose + oxygen
    • Cglucose + water → carbon dioxide + oxygen
    • Dglucose + carbon dioxide → water + oxygen
  3. 3.Which of the following processes require, and are dependent on, the activity of enzymes? 1. aerobic respiration 2. glucose → lactic acid 3. osmosis 4. anaerobic respiration in yeast

    Medium
    • A1 and 2
    • B1 and 3
    • C1, 2 and 4
    • DAll of them
  4. 4.What is produced by anaerobic respiration in humans?

    Easy
    • Aalcohol and carbon dioxide
    • Balcohol and lactic acid
    • Clactic acid only
    • Dcarbon dioxide only
  5. 5.Which substances are used during aerobic respiration? 1 carbon dioxide 2 glucose 3 oxygen 4 water

    Easy
    • A1 and 3
    • B1 and 4
    • C2 and 3
    • D2 and 4
  6. 6.What is the balanced chemical equation for anaerobic respiration in yeast?

    Medium
    • AC6H12O6 → 2CO2 + 6H2O
    • BC6H12O6 → 6CO2 + 6H2O
    • CC6H12O6 → 2C2H5OH + 2CO2
    • DC6H12O6 → 2C2H5OH + 2H2O
  7. 7.Which of these correctly shows the products produced by anaerobic respiration in yeast and in animals?

    Medium
    • AAnimals: lactic acid yes, carbon dioxide no; Yeast: lactic acid no, carbon dioxide no
    • BAnimals: lactic acid yes, carbon dioxide no; Yeast: lactic acid no, carbon dioxide yes
    • CAnimals: lactic acid no, carbon dioxide yes; Yeast: lactic acid yes, carbon dioxide no
    • DAnimals: lactic acid yes, carbon dioxide yes; Yeast: lactic acid no, carbon dioxide yes
  8. 8.During vigorous exercise, lactic acid builds up in muscles. How is this lactic acid removed during recovery?

    Medium
    • Aexcretion of lactic acid by the kidneys
    • Banaerobic respiration of lactic acid in the muscles
    • Caerobic respiration of lactic acid in the liver
    • Dexcretion of lactic acid by the lungs

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