Why Do We Respire?

          The process of oxidation of food into carbon dioxide and water to produce energy is called respiration. On the basis of presence of oxygen respiration is of two types :
(a)     Aerobic respiration : When break-down of glucose occurs with the use of O2 , it is called aerobic respiration. In this process there is complete breakdown of food, so maximum production of energy.



(b)     Anaerobic respiration : When breakdown of glucose occurs in lack or limited supply of O2 is called anaerobic respiration.

During heavy exercise, when the supply of oxygen to our muscle cell is insufficient, food breakdown occurs by anaerobic respiration.

       There are two types of respiration – aerobic and anaerobic respiration.
1.    Aerobic Respiration :     When the breakdown of food substances (like glucose) takes place in the presence of oxygen with the release of a large amount of energy, it is called aerobic respiration. In this process, carbon dioxide and water are released          as waste products.
     The overall equation for aerobic respiration is:

Most animals including humans and green plants respire aerobically.

2.    Anaerobic Respiration : Anaerobic respiration is the breakdown of food substances with the release of a small amount of energy in the absence of oxygen. It occurs in certain organisms like yeast and some bacteria. These organisms are called                    anaerobes.

     In th absence of oxygen, glucose breaks down into alcohol and carbon dioxide with the release of comparatively less energy.
    The equation for anaerobic respiration is:

Why Do We Respire?

Chapter 10: Respiration in Organisms

Cellular respiration takes place in the cells of all organisms. 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. Food can also be broken down, without using oxygen.

Why do we respire ?

We respire to use the oxygen, to oxidise our food and release energy. This is similar like burning but a slower process. It also needs respiratory enzymes .The job of your lungs is to provide your body with oxygen and to get rid of the waste gas, carbon dioxide. Your brain constantly gets signals from your body which detect the amount of oxygen and carbon dioxide in your blood.


  •    Exchange of gases or taking in O2 and giving out CO2 with the help of respiratory organs is called breathing. 
  •    The taking in of air rich in oxygen is called inhalation and giving out CO2 rich air is called exhalation. 
  •    It is a continuous process which goes on all the time and throughout the life of an organism.
  •    The number of times a person breathes in a minute is called the breathing rate. 
  •    Normal breathing of adult human beings at rest is about 15-18 per min. But it can change according to requirement of O2 by the body. 
  •    Thus, whenever a person needs extra energy breathing rate increases. 
  •    So, during heavy exercise, the breathing rate can increase upto 25 times per minute and also we take deep breaths to inhale more oxygen. 
  •    As a result more oxygen is supplied to our cells. 
  •    So speeds up the breakdown of food and more energy is released. 
  •    That is the cause we feel hungry after a physical activity.



Breathing (or ventilation) is the process of moving air into and from the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxygen.The breathing of all vertebrates with lungs consists of repetitive cycles of inhalation and exhalation through a highly branched system of tubes or airways which lead from the nose to the alveoli.[3] The number of respiratory cycles per minute is the breathing or respiratory rate, and is one of the four primary vital signs of life. Under normal conditions the breathing depth and rate is automatically, and unconsciously, controlled by several homeostatic mechanisms which keep the partial pressures of carbon dioxide and oxygen in the arterial blood constant.

How Do We Breathe?

How do we breathe?

The diaphragm is pulled flat, pushing out the lower ribcage and abdomen. At the same time, the muscles between your ribs pull your rib cage up and out. This expands the chest and draws air into the lungs. Air is pulled into your nose or mouth, and into your windpipe.

What Do We Breathe Out?

What do we breathe out ?

The role of the respiratory system is to breathe in oxygen and breathe out carbon dioxide. This is known as respiration. The cells of the body use oxygen to perform functions that keep us alive. The waste product created by the cells once they have performed these functions is carbon dioxide.

Breathing in Other Animals

Breathing in Other Animals
•    Animals such as elephants, lions, cows, goats, frogs, lizards, snakes, birds have lungs in their chest cavities like the human beings.
•    Respiration in insects: A cockroach has small openings on the sides of its body. Other insects also have similar openings. These openings are called spiracles. Insects have a network of air tubes called tracheae for gas exchange. This type of respiration is      called tracheal respiration. Oxygen rich air rushes through spiracles into the tracheal tubes, diffuses into the body tissue, and reaches every cell of the body. Similarly, carbon dioxide from the cells goes into the tracheal tubes and moves out through spiracles.     These air tubes or tracheae are found only in insects and not in any other group of animals.


•    Respiration in Earthworm: Earthworms breathe through their skin. This is called cutaneous respiration.The skin of an earthworm feels moist and slimy on touching. Gases can easily pass through them. Though frogs have pair of lungs like human                 beings, they can also breathe through their skin, which is moist and slippery by the process of diffusion.

Breathing in Other Animals

Breathing in other animals

Breathing in Other Animals. Just like human beings, animals also breathe. Breathing is the process of inhaling oxygen and exhaling carbon dioxide. Few organisms have lungs in their chest cavity which helps them to breathe.

Animals intake oxygen and release carbon dioxide. It is also known as breathing. This is mainly two phases.

Inspiration: It is the process by means of which oxygen is taken to the lungs.

Expiration: During expiration, carbon dioxide is expelled out from the respiratory organs into the environment.

Breathing Under Water

Breathing Under Water

Gills in fish help them to use oxygen dissolved in water. Gills are projections of the skin. Gills help in breathing. Gills are well supplied with blood vessels for exchange of gases. But breathing in water is quite difficult as water is dense and having less dissolved oxygen than air.

Breathing Under Water

Breathing under water

The fishes breathe by taking in water through its mouth and sending it over the gills. The oxygen dissolved in the water is extracted by the gills and the extracted oxygen is absorbed by the blood. This oxygen is then carried to all the parts of fishes for respiration.

Do Plants Also Respire?

Do Plants Also Respire?
    They also take in oxygen from the air and give out carbon dioxide. In the cells oxygen is used to break down glucose into carbon dioxide and water as in other organisms.

   In plants each part can independently take in oxygen from the air and give out carbon  dioxide. The leaves of the plants have tiny pores called stomata for exchange of oxygen and carbon dioxide. Like all      other living cells of the plants, the root cells also need oxygen to generate energy. Roots take up air from the air spaces present between the soil particles with the help of root hairs. Lenticels in old stems and     general surface of roots help in respiration.  Lenticells in old stem and general surface of roots help in respiration.

Do Plants Also Respire?

Do Plants also respire ?

Plants respire all the time, whether it is dark or light. However, they only photosynthesise when they are in the light. The table shows the difference between photosynthesis and respiration at different times of the day. Photosynthesis and respiration in plants during the day.

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