Respiration in Plants and Animals


The process of taking oxygen into the cells, using it for energy release & then eliminating the waste products like CO2 & H2O is known as respiration.

It is a very slow process. A number of enzymes help in the process of respiration.


The process of taking in O2 rich air into the lungs & giving out carbon dioxide-rich air is known as breathing.

The breathing process includes 2 steps –

Inhalation :

The process of taking in air is called inhalation.

Exhalation :

Giving out of the air is called exhalation.

Breathing involves the only exchange of gases.


Breathing Respiration
1 It is only a physical process in which oxygen is taken in and carbon dioxide is given out It is a
biochemical process in which glucose is oxidized and carbon dioxide and water are released
2 It occurs outside the cells It occurs inside the cells
3 There is no release of energy There is a
gradual and
step-wise release of energy
4 Enzymes are not involved in the process. Enzymes
are involved
in the



There are 2 types of respiration

Aerobic respiration

  • In this type of respiration complete oxidation of glucose takes place & CO2, H2O & Energy are released.
  • Aerobic respiration takes place in the presence of oxygen & is carried out in the bodies of almost all living animals & plants

Glucose \overset{{{{O}_{2}}}}{\mathop{{\xrightarrow[{Aerobic\,\,respiration}]{}}}}\, CO2 + H2O + Energy

Anaerobic respiration :

  • In anaerobic respiration, there is incomplete oxidation of glucose CO2, ethyl alcohol & energy are the end products.
  • Anaerobic respiration takes place in the absence of oxygen.

Glucose \overset{{Absence\,\,of\,\,{{O}_{2}}}}{\mathop{{\xrightarrow[{Anaerobic\,respiration}]{}}}}\, Alcohol + CO2 + Energy

  • Yeast & some bacteria show anaerobic respiration.
  • Anaerobic respiration in microorganisms present in food & alcohol causes fermentation.

Anaerobic Respiration in Human

  • During excessive physical exercise, anaerobic respiration takes place in muscle to produce lactic acid.
  • The accumulation of lactic acid in the muscle cause fatigue & pain.

Glucose \xrightarrow{{Absence\,of\,{{O}_{2}}}} Lactic acid + Energy


  • Like all other living organisms, plants also respire for their survival.  They also take in oxygen from the air and give out carbon dioxide. During this process, most of the plants use atmospheric oxygen to break down glucose into carbon dioxide and water with the release of energy.
  • In plants, breathing takes place through tiny holes or openings called stomata present under the leaves. Stomata trap air and the exchange of gases takes place inside the plant cells.

Stomal Apparatus :

  • A stomatal opening surrounded with two guard cells and several subsidiary cells is called stomatal apparatus. The opening and closing of the stomata is brought about by the expansion and contraction of the guard cells. Guard cells expand and contract due to the flow of water in and out of the cells. The exchange of gases in plants is not as fast as in animals.

Stomal Apparatus

  • Plant roots also respire. Roots take in oxygen from the air present between the soil particles.
  • Some of the woody stems take in air through openings called lenticels.

respiration in plants and animalsRespiration in Animals

 Respiration through moist skin

Eg. Frog & Earthworm

  • Respiration through the cell membrane

Eg. Amoeba

  • Respiration through Spiracles

Eg. Cockroach

  • Respiration through gills

Eg. Fishes

Respiratory System of Human

The respiratory system in human beings consists of the following organs

Nasal Cavity

  • Air enters the nose through the nostrils and reaches the nasal cavity.


  • The nasal cavity leads into the pharynx. From the pharynx, air passes into a rectangular chamber called the larynx


  • The trachea or windpipe is a delicate muscular tube situated in the front of the neck. It is 12 cm in length and 2.5 cm in diameter. The trachea divides into two bronchi.


  • Each bronchus leads to the lungs of its own side. Each bronchus then branches into smaller tubes known as bronchioles. They end in tiny globules called air sacs or alveoli where the exchange of gases takes place.


  • Lungs are two in number and are present in the chest cavity of the body. Air sacs are richly supplied with blood vessels. When air enters the lungs, the blood takes in oxygen and gives out carbon dioxide and water
  • Blood carries oxygen to all parts of the body from the lungs.
  • When we exhale, the carbon dioxide-rich air follows the reverse route finally moving out through the nose as shown below.

 Respiratory System of Human

Mechanism of Breathing

  • Breathing takes place with the help of the intercostal muscles between the ribs and the diaphragm. When we breathe in, the intercostal muscles contract and the ribs are pushed outwards. The chest cavity becomes larger and the air rushes into the lungs.
  • During breathing out, the intercostal muscles relax and the ribs move inwards. The chest cavity shrinks and the air containing carbon dioxide is pushed out of the lungs.

mechanism of breathing

  • Breathing rate : The number of times a person breathes in a minute is termed as the breathing rate. The normal breathing rate in adult at rest ranges from 12 to 20.

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