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Respiration theory Biology-day-3 Target-ssc-cgl-2018

Respiration theory Biology-day-3 Target-ssc-cgl-2018

Respiration theory Biology-day-3 Target-ssc-cgl-2018


Respiration takes place in our body all the time. During respiration, the energy stored in the food that we eat is utilised by the body of an organism. So, if any organism wants to get energy, merely eating food is not sufficient, but respiration is also necessary.

The process by which the energy stored in the food is released and utilised is called respiration. In respiration, an organism takes in oxygen and release carbon dioxide and water as waste product.

Respiration is the reverse process of photosynthesis. The equation of respiration is…

Glucose  +  Oxygen   →   Carbon  dioxide  +  water   +   energy

Respiration includes two parts..

  • Breathing (taking in oxygen and releasing carbon dioxide).
  • Using oxygen for releasing energy from food.


  • Respiration happens inside the cells. As respiration happens inside the cell, it is also called cellular respiration.
  • A cell organelle; called mitochondria is the site of cellular respiration.


There are two types of respiration…

Aerobic respiration  :

When the energy stored in the food is released with the help of oxygen, it is called aerobic respiration. It uses air and thus its name is aerobic respiration.

Glucose    Carbon  dioxide  +  water   +   energy  (in the presence of air)

All the organisms which obtain energy by aerobic respiration can’t live without air.

Anaerobic respiration  :

When the energy stored in the food is released without the help of oxygen, it is called anaerobic respiration. It does not use air and thus its name is anaerobic respiration. Yeast obtains energy by anaerobic respiration.

Glucose    Alcohol   +  water   +   energy  (in the absence of air)

All the organisms which obtain energy by anaerobic respiration can live without air.

Anaerobic respiration in muscles

When we do vigorous physical activity or workout, cells starts using oxygen at a faster rate. When the oxygen gets used up faster in the cell than can be supplied by the blood, then a temporary deficiency of oxygen occurs in the muscle cell. In such condition, anaerobic respiration starts in the muscles. Due to this, partial breakdown of glucose forms lactic acid. The accumulation of lactic acid in the muscle causes muscle cramps.

Respiration theory

  • The process of taking in and giving out air for respiration is called breathing.
  • Breathing involves two main steps, viz. inhalation and exhalation.
  • During inhalation, we breathe in air which is rich in oxygen.
  • During exhalation, we breathe out air which is rich in carbon dioxide.


The number of times a person breathes in a minute is called the breathing rate of that person. The average breathing rate in an adult human being at rest is 15-18 times a minute. The breathing rate in children is higher than the breathing rate of adults. Children breathe 20-30 times per minute. When we are doing normal activities, the rate of breathing is normal.

  • The rate of breathing increases when we do strenuous physical works such as running, swimming, jogging, etc.
  • The rate of breathing decreases when we take rest or when we are sleeping.

Respiration in humans

Main organs of human respiratory system are Nose, Nasal passages, Trachea, Bronchi, Lungs and Diaphragm.

Our nose has two holes called nostrils. There is a passage behind the nostrils. This passage is known as the nasal passage. The nasal passage joins the nostrils with trachea. Trachea branches into two smaller tubes called bronchi. The two bronchi are connected to the two lungs. Bronchi is further divided into very small tubes called bronchioles.  The exchange of gases between the air and blood takes place across the walls of the alveoli. Oxygen is carried by haemoglobin to different parts of the blood.

Sneezing : When we inhale air containing dust, smoke, pollen etc., we sneeze to expel them.

Yawning : If the proportion of oxygen reduces in the blood, we yawn.

Smoking : Smoking tobacco in the form of beedi, cigarette, cigar etc. is injurious to health. Harmful effects of smoking are…

  • It destroys lung tissues.
  • It causes lung cancer.
  • It enhances the chances of heart diseases.

Respiration theory
Respiration in other organisms

  • Some organisms like earthworm, fish, cockroach, grasshoppers, ants, flies do not have lungs. Generally, insects do not have lungs for breathing.
  • Earthworm breathes through its skin.
  • Frogs breathe through lungs on land and through skin in water.
  • Fish has gills for breathing under water.
  • Remember, dolphins and whales are sea animals, but they have gills to breathe.
  • All insects breathe through tiny holes called spiracles and thin air tubes called tracheae.

Respiration in plants

Plants respire through leaves and roots. The exchange of gases takes place in the stomata of the leaves. Also, plants respire through their root hair.


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