Anatomy: Animals Inside


How do certain animals use gills to breathe?

Gills may be external extensions of the body surface such as those found in aquatic insect larvae and some aquatic amphibians. Diffusion of oxygen occurs across the gill surface into capillaries, while carbon dioxide diffuses out of the capillaries into the environment. Fish and some other marine animals also have internal gills: Water enters the animals through the mouth, then flows over the gills in a steady stream and out through gill slits. Although some animals with gills spend part of the time on land, they all must spend some time in moist, wet environments in order for the gills to function.


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