Class 7 Respiration in Organisms Notes for exams

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RESPIRATION IN ORGANISMS

The cells of living organisms require a constant supply of oxygen to release energy. The energy released is used to carry out cellular processes.

HUMAN RESPIRATORY SYSTEM

• Breathing is a part of respiration and it is also referred to as external respiration.

Breathing It is the process by which organism takes in oxygen continuously and releases carbon dioxide into the environment.

• 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. Duringexhalation, 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

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 oxidizes more food to release more energy required.

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 throughout 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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