Cellular Respiration: Definition and Meaning, Catabolism, Anabolism (For CBSE, ICSE, IAS, NET, NRA 2022)

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Definition and Meaning

  • A set of metabolic reactions and processes occurring in the cells of organisms that convert chemical energy from oxygen molecules or nutrients into adenosine triphosphate (ATP) thereby releasing waste products is known as Cellular respiration.
  • A cell releases chemical energy to fuel cellular activity during respiration.
  • A set of chemical reactions carried out for maintaining the living state of the cells in an organism is called metabolism.
  • In a simple way we can say that Cellular respiration is a metabolic pathway that breaks down glucose and produces ATP.
Cell Respiration in a Typical Eukaryotic Cell

Two Categories

Two Categories of Cellular Respiration


  • It is the process of breaking molecules to obtain energy.
  • Here big complex molecules are broken down into smaller, easier to absorb molecules.
  • Hormones involved are namely adrenaline, cytokine, glucagon, and cortisol.
  • Some of the examples of catabolic processes are proteins becoming amino acids, glycogen breaking down into glucose.
  • The potential energy gets changed into kinetic energy.


  • It is the process of synthesizing all compounds being required by the cells.
  • It helps in building molecules required for maintaining the functionality of the body.
  • Estrogen, testosterone, growth hormones, etc. are some of the hormones involved in the process.
  • Formation of polypeptides from amino acids, glucose forming glycogen, etc. are some of the examples.
  • Here the kinetic energy is converted into potential energy.

Aerobic Respiration

  • In aerobic respiration there is an aerobic catabolism of nutrients to carbon dioxide, water, and energy.
  • The molecular oxygen is the final electron acceptor.
  • To obtain energy from glucose, most eukaryotes and prokaryotes use aerobic respiration.
  • This respiration requires pyruvate to the mitochondria to be fully oxidized by the citric acid cycle.

  • The reaction can occur spontaneously is being shown by the negative ΔG.

Anaerobic Respiration

  • In this respiration the glucose breaks down without oxygen.
  • This respiration produces lactic acid, rather than carbon dioxide and water which can lead to painful muscle cramps.
  • The process still uses a respiratory electron transport chain.
  • Less-oxidizing substances such as nitrate (NO3 −) , fumarate, sulphate (SO42 −) , or Sulphur (S) are used.


  • It is defined as a metabolic pathway that takes place in the cytosol of cells in all living organisms.
  • It occurs with or without the presence of oxygen.
  • The process converts one molecule of glucose into two molecules of pyruvate (pyruvic acid) in aerobic conditions.
    • Generating energy in the form of two net molecules of ATP.
Structure of Glycolysis

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