The sum total of physical and chemical processes by which oxygen and carbohydrates (main food nutrient) etc. are assimilated into the system and the oxidation products like carbon dioxide and water are given off.
Breathing:( External Respiration):-
The process of exchange of oxygen from the atmosphere with carbon dioxide produced by the cell is known as breathing.
A pair of external nostrils---->nasal chamber through nasalpassage---->pharynx--->glottis---->larynx--->trachea--->left and right primary bronchi--->secondary and tertiary bronchi----->brinchioles---> vascularised bag like structures (alveoli)or air sacs.
Lung is the respiratory organ in terrestrial organisms from where exchange of gases take place.
Each lung is covered with double layered membrane known as pleura with pleural fluid between them.
Respiratory organs in animals:-