Breathing in other animals

Animals live in very different places. Birds fly, fish swim — so how do they all breathe?

Birds, elephants, lions, cows, goats, lizards and snakes all breathe with lungs. But their lungs are not built the same; the structure differs a lot from animal to animal.

Most water animals, like fish, have special structures called gills. Water has oxygen dissolved in it. Gills are packed with blood vessels, so oxygen from the water passes into the blood, and carbon dioxide passes out into the water, right across the gills.

Amphibians like frogs live both in water and on land, and use different body parts at different stages of life:

• A tadpole breathes through gills.
• An adult frog uses lungs on land, and its skin to exchange gases when it is in water.

This helps frogs survive in both places, and shows how animals have adapted over time to where they live.

Earthworms have no lungs or gills: they use their moist skin to exchange oxygen and carbon dioxide. That is why an earthworm must stay damp.

So each animal breathes in the way its home demands. Besides the digestive, respiratory and circulatory systems, there are other body systems working together to keep us alive, which you will study in higher grades.