Q1.
You may have observed birds flying and fish swimming. How do they breathe?
Answer
Birds breathe through lungs, like humans. Fish breathe through gills. Different animals have different breathing organs to suit the habitat they live in.
| Animal | Breathing organ | How it works |
|---|---|---|
| Birds, elephants, lions, cows, goats, lizards, snakes | Lungs | All have lungs, but the structure of the lungs is quite different in each of them |
| Most aquatic animals, such as fish | Gills | Gills are richly supplied with blood vessels; oxygen and carbon dioxide are exchanged between the blood and the gases dissolved in the water |
| Frog — tadpole stage | Gills | The young tadpole lives entirely in water |
| Frog — adult | Lungs on land, skin in water | An amphibian uses different body parts at different stages and in different places |
| Earthworm | Moist skin | Oxygen and carbon dioxide are exchanged straight through the damp body surface |
Why it happens: in every case the gas has to pass through a thin, moist surface that is well supplied with blood. Lungs keep that surface inside the body, safe from drying; gills spread it out in water, where oxygen is dissolved; the earthworm simply keeps its whole skin moist. Each design suits its habitat — which is why an earthworm dries up and dies on hot ground, and a fish out of water cannot breathe even though there is plenty of oxygen around it.