Request a call back

Join NOW to get access to exclusive study material for best results

Respiration in Animals

Respiration in Animals Synopsis




  • Food obtained in nutrition is used to release energy required to carry out various metabolic processes.
  • Respiration is a catabolic process of releasing energy from the simple sugar glucose for carrying out various life processes.

  • The energy required for all cellular activities is obtained by the oxidation of glucose. If glucose is not available, then the cells may break down proteins and fats to produce glucose. This glucose is then oxidised further to fulfil the respiratory needs of the cell. 
  • The first step towards obtaining energy is six-carbon glucose is broken down into two molecules of three-carbon pyruvate. This process takes place in the cytoplasm.

Characteristics of Respiration

  • The breakdown of glucose to carbon dioxide and water does not occur in a single step. It involves a series of chemical reactions. It consists of three main phases: 
    • Glycolysis (glucose → pyruvate; occurs in the cytoplasm)
    • Krebs cycle (pyruvate → CO2 + H2O + ATP; occurs in mitochondria)
    • Electron transport (Energy-rich compounds → ATP; occurs in mitochondria)
  • Each breakdown step is carried out by a specific enzyme.
    • Dehydrogenase → Removal of hydrogen
    • ATP synthase → Synthesis of ATP 
  • A small amount of energy liberated in the breakdown of the glucose molecule is released as heat energy. But a major part of it is converted into chemical energy in the form of Adenosine Triphosphate (ATP). ATP has high energy content. It is also known as energy currency of the cell.


Types of Respiration



  • Breathing is the biological process of inhaling and exhaling of the gases between the cells and the environment. 
  • Breathing involves taking in of oxygen-rich air or inhalation (inspiration) and giving out carbon dioxide-rich air or exhalation (expiration).

Breathing and Respiration



Respiration in Animals

  • Depending on the level of organisation and habitat, the respiratory organs are different in different animals.
  • Characteristics of respiratory organs in animals:
    1. They have large surface area to get enough oxygen. 
    2. They have thin walls for easy diffusion and exchange of gases. 
    3. They have rich blood supply for transport of respiratory gases.

Respiration in Amoeba

  • Amoeba is a unicellular organism which lives in fresh water. This organism does not have a specialized organ to do the process of respiration. 
  • In amoeba respiration takes place through its cell membrane also called plasma membrane.

Respiration in Earthworm

  • In earthworms there is no specialized organ for respiration. The respiration process takes place through its moist, thin and highly vascular skin. 
  • The oxygen gas absorbed by the skin diffuses into the blood and transported to all the cells of the body. 
  • In the cells, oxygen is used up for oxidation of food. During this process, carbon dioxide is produced.
  • Then, this carbon dioxide mixes in the blood and diffused out of the body through its moist skin.


Respiration in Fish

  • In aquatic animals such as fish respiration takes place through special respiratory organs called gills.
  • Gills are present on both the sides of the head of fish. The gills are covered by gill covers also called operculum. 
  • The gills of fish are very efficient as they can extract about 80% oxygen dissolved in water. 
  • The gills have an important role in maintaining the right balance of salts in the body.