Breathing : NCERT / CBSE Notes

Breathing In Humans
The cells of living organisms require a constant supply of oxygen to release energy. This is done by a process called breathing.  Breathing involves two steps - one inhalation and one exhalation. The breath rate of human beings is 15 – 18 breaths a minute.
Breathing  In Humans, CBSE / NCERT Notes, Class 7

Air passes through the tiny hair in the nasal cavity, and then through the pharynx, larynx and windpipe before reaching the lungs.  The hairs in the nasal cavity prevent the entry of dust particles and pollen. The mucous lining is present from the nasal cavity to the lungs.
Lungs are situated inside the chest cavity, and they rest on a large muscular sheet called the diaphragm, which forms the floor of the chest cavity. When you breathe in, your diaphragm and rib cage get into action.  The diaphragm is protected by the rib cage.  The diaphragm plays an important role in inhalation and exhalation.
  • Breathing is a mechanical process that involves two steps - taking in oxygen from the air and giving out carbon dioxide to the air.
  • The action of taking in air rich in oxygen is termed as inhalation.
  • The action of giving out air rich in carbon dioxide is called exhalation.
  • One inhalation and one exhalation make up one breath.
  • The number of times you breathe in one minute is called the breathing rate.
  • After air enters the nostrils, it passes through the nasal cavity, where tiny hair present inside the cavity trap unwanted particles such as smoke, dust and pollen. From the nasal cavity, air travels through the pharynxlarynx, and windpipe before it reaches the lungs located in the chest cavity.
  • The lungs rest on a large muscular sheet, called the diaphragm, which forms the floor of the chest cavity.
  • When inhaling, the rib cage moves outwards, and the diaphragm contracts and moves downwards. The rib cage expands and this increases the space in the chest cavity. Air rich in oxygen is pulled into the lungs.
  • When exhaling, the ribs move inwards, and the diaphragm relaxes and returns to its normal position. The rib cage contracts and this reduces the size of the chest cavity. Air rich in carbon dioxide is pushed out of the lungs.
Breathing In Animals, Insects

An insect does not have any respiratory organs. For respiration, they have special organs called spiracles. Oxygen reaches to the cells directly through the spiracles by means of diffusion. 

The skin is the respiratory organ in animals like frogs and earthworms. The skin in these animals is moist and slimy, which makes it easier for oxygen to diffuse in and carbon dioxide to diffuse out of the body. However, frogs are special animals. They can breathe through their skin in water, while on land they can breathe through their skin as well as their lungs.
The respiratory organs in fish are the gills. Fishes take in oxygen in dissolved form.  During respiration, water enters the body through the mouth, and then passes through the gills and comes out of the operculum. The gills take in the oxygen dissolved in the water and give out carbon dioxide.
    • In insects, air enters through small openings on the body, called spiracles, and finally reaches the trachea, a network of air tubes. The oxygen in the air diffuses into the tissues and is ultimately absorbed by the cells. The carbon dioxide released by the cells is carried by the trachea and given out through the spiracles.
    • Frogs and earthworms have a moist and slimy skin, which makes it easier for oxygen to diffuse into and carbon dioxide to diffuse out of the body.
    • Fish have special structures called gills that help in breathing.
    • The gills of fish have numerous blood vessels that take in dissolved oxygen from the surrounding water, and give out carbon dioxide.

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