(59) 12. Respiration (Cambridge IGCSE Biology 0610 for exams in 2023, 2024 and 2025)

Introduction to Respiration

• Respiration is a chemical process that breaks down glucose to release energy for various cellular processes.

• Occurs in almost all body cells and is enzyme-controlled.

• Important distinction: Breathing is a physical process (inhaling oxygen and exhaling carbon dioxide), while respiration is the chemical process that generates energy from glucose.

Uses of Energy in Living Organisms

• Energy released during respiration is utilized for:

  • Muscle contraction

  • Protein synthesis

  • Cell division

  • Active transport

  • Growth

  • Transmission of nerve impulses

  • Maintenance of constant body temperature

Investigating the Effect of Temperature on Respiration

• Yeast Respiration Experiment:

  • Use yeast and glucose solution in a test tube.

  • Control temperature with a water bath (initially at 30 degrees Celsius).

  • Add methylene blue as an indicator and record the time for it to turn colorless.

  • Faster color change indicates a higher respiration rate.

• Independent Variable: Temperature (varied using different water baths)

• Dependent Variable: Rate of respiration (converted from time taken for color change using formula: rate = 1/time).

• Variables to control:

  • Amount of methylene blue

  • Volume of yeast suspension

  • Concentration of glucose

  • pH level

• Observation: As temperature rises to 40 degrees Celsius, respiration rate increases due to more collisions between enzymes and substrates. Beyond 40 degrees, respiration rate decreases as enzymes start to denature.

Types of Respiration

Aerobic Respiration

• Definition: Chemical reactions that use oxygen to break down nutrients to release energy.

• Word Equation: Glucose + Oxygen → Carbon Dioxide + Water + Energy

• Balanced Chemical Equation: C6H12O6 + 6O2 → 6CO2 + 6H2O

Anaerobic Respiration

• Definition: Chemical reactions occurring in the absence of oxygen, releasing energy from glucose.

• Less energy is produced compared to aerobic respiration.

• In Yeast:

  • Word Equation: Glucose → Alcohol + Carbon Dioxide

  • Balanced Equation: C6H12O6 → 2C2H5OH + 2CO2

• In Muscle Cells during vigorous exercise:

  • Word Equation: Glucose → Lactic Acid

  • Provides energy when aerobic respiration is insufficient due to lack of oxygen.

  • Lactic acid can cause fatigue and muscle cramps and must be removed.

Oxygen Debt and Recovery

• After exercise, elevated heart rate helps transport lactic acid to the liver.

• In the liver, lactic acid is converted back to carbon dioxide and water through aerobic respiration using oxygen.

• This phenomenon of experiencing a temporary oxygen shortage is termed oxygen debt.

• Recovery involves deeper and faster breathing to repay oxygen debt accumulated during strenuous activity.

Comparison of Aerobic and Anaerobic Respiration

Conclusion

• The study of respiration is crucial for understanding energy production in living organisms.

• Both aerobic and anaerobic respiration play vital roles but differ significantly in processes and energy yield.