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Breathing - Lesson Summary

The cells of living organisms require a constant supply of oxygen to release energy. The energy released is used to carry out cellular processes.
It is the process by which organism takes in oxygen continuously and releases carbon dioxide into the environment.
  • Breathing is a part of respiration and it is also referred to as external respiration.
  • Breathing merely involves exchange of gases between the organism and the environment.
  • Breathing is purely a physical process.
  • Breathing is brought about by coordination between lungs, ribs and the diaphragm. Diaphragm is a thin sheet of skeletal muscle that separates the thoraciccavity from the abdominal cavity.
  • It is a mechanical process that involves two steps – inhalation and exhalation.

a) Inhalation is the action of taking in air rich in oxygen. During inhalation, the rib cage moves outwards and the diaphragm contracts to move downwards. As the rib cage expands, the space in the chest cavity increases allowing air rich in oxygen enter the lungs.
b) Exhalation is the action of giving out air rich in carbon dioxide to the environment. During exhalation, the ribs move inwards and the diaphragm relaxes to return to its normal position. The contraction of rib cage reduces the size of the chest cavity. Now air rich in carbon dioxide is driven out of the lungs. RESPIRATION  BREATHING Respiration involves both physical and chemical processes. Breathing is purely physical process. Respiration involves oxidation of food to release energy. Breathing is the action of taking in oxygen and giving out carbon dioxide. Respiration is the sum of external and internal respiration. Breathing is the sum of inhalation and exhalation. Respiration releases energy. Breathing does not release any energy. Respiration takes place in all the cells of the body. Breathing takes place only in the organs involved in the process. Respiration involves breathing and and oxidation of food in side the cell. Breathing is a part of respiration.

Breath and breathing rate
  • One complete breath accounts for the sum of one inhalation and one exhalation.
  • Breathing rate is the number of times a person breathes in one minute. Normal breathing rate in an individual during rest is 15 – 18 breaths per minute. Breathing rate increases drastically during exercise and running.

Respiratory system in human beings
Different organs of respiratory system include nostrils, larynx,trachea, bronchi, a pair of lungs, bronchioles and alveoli.

Mechanism of breathing 
a) During inhalation, nostrils take in the air which is moistened by the mucous secreted by the inner lining of the nose.
  • The mucous lining present in the respiratory tract keeps the passage moist from the nasal cavity to the lungs.
  • Mucous and the hair in the nose entangle the dirt, pollen and other dust particles and prevent them from entering our nose.

b) Air passes through the pharnyx and enter the trachea made up of rings of cartilage. Trachea is also called as wind pipe.

c)Trachea bifurcates into two stems called as bronchi (singular: bronchus).

d) Lungs are situated inside the chest cavity and they rest on a large muscular sheet called the diaphragm.
  • Diaphragm 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. Movement of diaphragm is brought about by special musculature.

e) Each bronchus enters the lung on either side and gives out repeated branches named as bronchioles inside the lung.

f) Bronchioles supply individual cells of the lung named as alveoli (singular: alveolus). Each lung is made up of 300 million alveoli.
  • A group of alveolar cells are surrounded by blood vessels.
  • Oxygen that enters the lungs is exchanged with carbon dioxide from the tissues at this alveolar region.
  • Carbon dioxide is taken out in the same path through which oxygen entered inside.

g) Carbon dioxide is released through nostrils by the process of exhalation.
h) During exercise, breathing rate increases so as to obtain more amount of oxygen which in turn oxidises more food to release more energy required.

Respiration in lower animals
Respiration is a vital life process of all the cells in found in animals.
  • Different animals possess different structures for respiration.
  • Lower organisms respire through their cell membrane which helps in diffusion of gases.
  • Organisms like insects respire through air holes called as spiracles.

Types of respiration based on structures Different types of respiration based on the structures used for the process are cutaneous respiration, branchial respiration and pulmonary respiration.
  • The organisms exhibiting cutaneous respiration respire through skin. e.g. Earthworms, Frogs, Toads .       
  • The organisms exhibiting branchial respiration respire through gills. e.g. Fish, Aquatic organisms.
  • The organisms which exhibit pulmonary respiration respire through lungs. e.g. Frogs, Reptiles,Birds and Mammals.

Respiration in lower organisms
Unicellular organisms like amoeba and paramecium respire through their cell membrane.
  • Cell membrane is thin and permeable to gases.
  • They take in oxygen through entire body surface and give out carbon dioxide.
  • Exchange of gases takes place through the cell membrane by the process of diffusion.
  • Hydra respires through its moist outer surface by the process of diffusion.

Respiration in earthworms
Earthworms exhibit cutaneous respiration i.e. respiration by skin.
  • Earthworms do not possess special organs for respiration.
  • They always secrete slimy secretion on to the skin which keeps it moist.
  • The skin in these animals is moist and slimy which makes it permeable for oxygen to diffuse in and carbon dioxide to diffuse out of the body.
  • As the earthworms cannot breathe in waterlogged conditions, they come out on to the soil during rainy season to obtain oxygen required for respiration.

Respiration in insects
An insect body is covered with air holes called as spiracles.
  • Air enters through these air holes on the body and finally reaches the trachea.
  • Trachea are a network of fine air tubes extending through out the body.
  • Trachea help in circulating the oxygen throughout the body.
  • 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.

Respiration in fishes
Fish are the aquatic vertebrates which respire through structures called as gills. This is called as branchial respiration.
  • Gills are present on either side of the head and are supplied by rich blood vessels.
  • Fish obtain oxygen dissolved in water.
  • During respiration, water enters the body through mouth, passes through gills and comes out of the operculum.
  • Exchange of gases takes place in the gills of fish supplied by numerous blood vessels.
  • They accept oxygen into the body and expel out carbon dioxide.

Respiration in frogs
Frog is an amphibian having two lives, one in water and one on land.
  • Frogs are the only organisms which exhibit cutaneous, branchial and pulmonary respiration in during different stages of their life cycle.
  • Adult frogs can breathe through their skin. Skin is moist and slimy helping the animal to respire through skin under water as well as on land. This is termed to be cutaneous respiration.
  • Adult frogs while on land respire through lungs. Lungs are the respiratory organs which help in exchange of gases. This is termed to be pulmonary respiration.
  • Tadpoles, the larval stages of frog live in water. They respire through their gills as they do not possess well developed lungs. This is termed to be branchial respiration. 


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