NCERT Exemplar Class 11 Biology chapter 17 Breathing and Exchange of gases

268 BIOLOGY

C HAPTER 17
BREATHING AND EXCHANGE OF G ASES
17.1 Respiratory As you have read earlier, oxygen (O2) is utilised by the organisms to
Organs indirectly break down simple molecules like glucose, amino acids, fatty
acids, etc., to derive energy to perform various activities. Carbon dioxide
17.2 Mechanism of
(CO2) which is harmful is also released during the above catabolic
Breathing
reactions. It is, therefore, evident that O2 has to be continuously provided
17.3 Exchange of to the cells and CO2 produced by the cells have to be released out. This
Gases process of exchange of O2 from the atmosphere with CO2 produced by the
17.4 Transport of cells is called breathing, commonly known as respiration. Place your
Gases hands on your chest; you can feel the chest moving up and down. You
know that it is due to breathing. How do we breathe? The respiratory
17.5 Regulation of organs and the mechanism of breathing are described in the following
Respiration sections of this chapter.
17.6 Disorders of
Respiratory 17.1 RESPIRATORY ORGANS
System
Mechanisms of breathing vary among different groups of animals
depending mainly on their habitats and levels of organisation. Lower
invertebrates like sponges, coelenterates, flatworms, etc., exchange O2
with CO2 by simple diffusion over their entire body surface. Earthworms
use their moist cuticle and insects have a network of tubes (tracheal
tubes) to transport atmospheric air within the body. Special vascularised
structures called gills (branchial respiration) are used by most of the
aquatic arthropods and molluscs whereas vascularised bags called lungs
(pulmonary respiration) are used by the terrestrial forms for the exchange
of gases. Among vertebrates, fishes use gills whereas amphibians, reptiles,
birds and mammals respire through lungs. Amphibians like frogs can
respire through their moist skin (cutaneous respiration) also.