Definition of Respiration: Chemical Reactions that break down molecules of nutrients in living cells to release energy

The energy released from Respiration is used for the following purposes:

  • Passage of nerve impulses throughout the nervous system
  • Creating new cells
  • Cell Division
  • Physical Growth
  • Protein Synthesis
  • Homeostasis (regulation of internal body temperature)
  • Active Transport
  • Muscle Contraction
The enzymes in cells are involved in the process of Respiration

Types of Respiration

There are two types of Respiration:

  1. Aerobic Respiration
  2. Anaerobic Respiration

Aerobic Respiration

Aerobic Respiration is what your body would be performing most of the times as it releases vast amounts of energy through the breakdown of glucose in food in the presence of oxygen gas.

Chemical Formula for Aerobic Respiration: C6H12O6 + 6O2  =  6CO2 + 6H2O

Anaerobic Respiration

Anaerobic Respiration releases relatively lesser amounts of energy through the breakdown of glucose in food in the absence of oxygen gas.

Chemical Formulas for Anaerobic Respiration:

  • In Muscles (in Humans): Glucose is broken down to Lactic Acid - C6H12O6 = 2 C3H6O3
  • In Yeast:  Glucose is broken down to ethanol + Carbon Dioxide - C6H12O6 = 2 C2H5OH +  CO2

Oxygen Debt

  • Anaerobic respiration in Humans is very disadvantageous as it only produces 1/20th of Glucose as Aerobic respiration does. It also produces Lactic Acid which is a poisonous substance.
  • The excess collection of Lactic acid in Muscles can lead to temporary muscular pain during exercise.
  • When Lactic Acid is produced from Anaerobic Respiration, it is transported in the blood to the heart towards the Liver and Kidneys where it is oxidised and broken down.
  • This is an oxygen intensive process which is why once a person in Oxygen Debt keeps breathing heavily even after they have completed their physical activity.

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Excretion in Humans - IGCSE Biology 2020-21 - IGCSE Pro
Excretion is one of the seven life processes and is the process which means the removal of waste and toxic products form the body.