Whit is Respiration?

Respiration is a bio-chemical process which involves:

  • Intake of environmental oxygen.
  • Oxidation of food (simple food molecules such a glucose)
  • Removal of carbon dioxide produced in oxidation.
  • Released of energy which is changed into biological useful form of energy ATP (adenosine triphosphate) molecules.

Thus, respiration is the process which involves exchange of environmental oxygen with carbon dioxide produced in the body during oxidation of food for the release of energy.

Breathing and Respiration

Mechanism by which an organism obtains oxygen from the environment and removes carbon dioxide is called breathing. Thus, intake of fresh air from the environment and removal of foul air (air having more CO2) from the body is called breathing. It is a physical process. Respiration is more complex process it includes:

1. Breathing

2. Oxidation of digested food occurring in the cell in order to release energy.

Energy produced during respiration it utilized from performing various metabolic activities (i.e. biological functions) essential for survival and maintenance of an organism.

Respiration is a biochemical process taking place in the cytoplasm and mitochondria. It occur in many steps and requires many enzymes. Main outcome of respiration is the release of energy by oxidation of food such as glucose.

Difference between breathing and



  1. It is a physical process and involves inspiration of fresh air and expiration of foul air. 
  2. It occur outside the cell and hence it is an extracellular process.
  3. It does not release energy, it rather used energy.
  4. No enzymes is involved in this process.
  5. It occur in certain organ only (lungs, gills, etc.)

 I. It is a biochemical process which involves exchange of gages and oxidation of food.

 II. It occur within the cell and hence it is an intracellular process.

 III. It released energy in the form of ATP.

 IV. It involves a large number of enzymes.

V. It occur in all cell of the body.


Difference between combustion (burning) and respiration.

Combustion (burning)


  1. 1. It is a physic-chemical process.

It is a bio-chemical process.

  1. 2. It is non-cellular.

It occur in cell.

  1. 3. In its many chemical bond breaks simultaneously, releasing a large amount of energy at a time.

In it chemical bonds break in steps, releasing energy in steps.

  1. 4. Temperature becomes very high.

Temperature remains low within limits.

  1. 5. Light is oftenly produced.

No light is produced.

  1. 6. It is not controlled by enzymes.

It is an enzymatically controlled process.

  1. 7. It is an uncontrolled process.

It occur in a controlled manner.

  1. 8. No intermediates are produced in it,

Several intermediates are produced in it.

  1. 9. ATP is not formed.

Most of the energy is trapped in ATP molecules.

10. Most of the energy released dissipates as heat.

Little energy produced is lost.


Types of respiration.

Oxidation of food for the release of energy may occur in presence or absence of oxygen. Hence, respiration is of two types as:

I.            Aerobic respiration: Majority of organisms accepts certain anaerobic bacteria, yeast and endoparasites use molecular oxygen for oxidation of food to release energy. When food is oxidized in the presence of oxygen, the respiration is said to be aerobic. Organisms having aerobic respiration are called aerobes. During aerobic respiration, food (glucose) is completely broken down in carbon dioxide and water by the process of oxidation. This results in the production of energy (ATP).

C6H12O6 +     6O2                 ------>       6CO2                 +     6H2O   +   Energy

(Glucose)         (Oxygen)                           (Carbon dioxide)         (Water)

The above shown reaction occurs in both cytoplasm and mitochondria of the cells. It occurs in many steps and requires many enzymes. In cytoplasm glucose is changed to pyruvic acid and the process is called glycolysis. During glycolysis no oxygen is needed. Pyruvic acid by a cyclic process is called Krebs’s cycle is oxidized to form carbon dioxide and water with release of more energy.

glycolysis                            Krebs’s cycle ECT

Glucose   -------------->   pyruvic acid  -------------------->   CO2   + H2O +Energy

No oxygen                                    O2 required

II.            Anaerobic respiration: It occurs in few organisms, such as certain anaerobic bacteria, yeast and many endoparasites like Taenia. It also occurs in our muscles during vigorous muscular activity, when oxygen gets used up faster than it is available to muscles cells. It also occurs in human red blood corpuscles.

It occurs in absence of molecular oxygen. It is also known as fermentation. In this process food is incompletely degraded so, only a part of energy (15%) is released. Organisms showing anaerobic respiration are called anaerobes.

In case of bacteria, muscles and endoparasites the end products of anaerobic respiration is lactic acid. But is case of yeast and some plants the end product of anaerobic respiration is ethyl alcohol. The overall equation for this is given here;

In yeast:

Glycolysis                         Fermentation

Glucose   ---------------> Pyruvate ------------------> C2H5OH + H2O + Energy

No oxygen                  no Oxygen           ethyl alcohol

In muscles:

Glycolysis                         Fermentation

Glucose   ---------------> Pyruvate ------------------>Lactic acid + Energy

No oxygen                          no Oxygen



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