Respiration in organisms

Start music   Jan 11 2017 || 1:09 PM

Cellular respiration

It is the process of breakdown of food in the cell with the release of energy

Cellular respiration takes place in the cells of all organisms


Aerobic respiration

  • In the cell, the food (glucose) is broken down into carbon dioxide and water using oxygen
  • When breakdown of glucose occurs with the use of oxygen it is called aerobic respiration



Glucose (with the use of O2)à Carbon dioxide + water +energy





Anaerobic respiration

  • Food can also be broken down, without using oxygen.
  • This is called anaerobic respiration
  • Organisms such as yeast can survive in the absence of air. They are called anaerobes.

Glucose (without the use of O2)à Carbon dioxide + alcohol +energy





  • Our muscle cells can also respire anaerobically, but only for a short time.
  • This happens during heavy exercise, fast running, cycling, or heavy weight lifting
  • Here the demand for energy is high but supply of O2 to produce the energy is limited



Glucose (absence of O2)à Lactic acid +energy





  • Accumulation of lactic acid causes muscle cramps
  • Any increase in the supply of oxygen results in the complete breakdown of lactic acid into carbon dioxide and water



  • Taking in air rich in O2 (inhalation) & giving out air rich in CO2 (exhalation)
  • The percentage of O2 and CO2 in inhaled are 21% and 0.04% respectively
  • The percentage of O2 and CO2 in the exhaled air are 16.4% and 4.4% respectively
  • The number of times a person breathes in a minute is termed as the breathing rate
  • On an average, an adult human being at rest breathes 15-18 times in a minute.
  • During heavy exercise, the breathing rate can increase up to 25 times per minute


Lungs and Chest cavity

  • Lungs are present in the chest cavity, surrounded by ribs on the sides
  • A large, muscular sheet called diaphragm forms the floor of the chest cavity


Mechanism of breathing

  • When we inhale air, it passes through our nostrils into the nasal cavity
  • From the nasal cavity, the air reaches our lungs through the windpipe
  • During inhalation, ribs move up and outwards and diaphragm moves down
  • This movement increases the volume in our chest cavity for air to fill in
  • During exhalation, ribs move down and inwards, while diaphragm moves up to its former position
  • This reduces the size of the chest cavity and air is pushed out of the lungs


Breathing in other animals


  • Have small openings called spiracles on the sides of its body
  • Have a network of air tubes called tracheae for gas exchange



  • Breathe through their skins which is moist and slimy



  • They have lungs, yet they can still breathe through their skin



  • They have gills which are supplied with blood vessels, which can help them breathe O2 dissolved in water


Respiration in plants

  • They also take in O2 from air and give out CO2 like humans