Lesson 1 of 11 · 6 min

Respiratory organs in animals

NCERT §14.1

Before the gun goes off, Meher watches an earthworm the groundskeeper has turned up at the edge of the track. It has no lungs at all, and yet it breathes.

The story this chapter follows: Meher's 800 m at Sports Day

Meher lines up for the 800 m at her school's Sports Day. At the start line her breathing is slow and easy; by the final lap she is gasping; and for a full minute after she crosses the line she is still breathing hard, hands on her knees. Every idea in this chapter shows up somewhere on that morning.

The lesson in notes

In short

Breathing, or respiration in the everyday sense, is the exchange of O₂ from the atmosphere with the CO₂ produced by cells. The mechanism varies mainly with habitat and level of organisation.

Lower invertebrates such as sponges, coelenterates and flatworms exchange gases by simple diffusion over the whole body surface.

Earthworms use their moist cuticle; insects have a network of tubes called tracheae that carry air within the body.

Special vascularised structures called gills are used by most aquatic arthropods and molluscs (branchial respiration); lungs are used by terrestrial forms (pulmonary respiration).

Among vertebrates, fishes use gills, while amphibians, reptiles, birds and mammals breathe through lungs.

Amphibians such as frogs can also exchange gases through their moist skin (cutaneous respiration).