Page 56 - One Million Things: Animal Life - The Incredible Visual Guide

RESPIRATION

Animals need oxygen to release the energy
in their cells that powers all life activities. The
energy-liberating process, called cell respiration,
also releases waste carbon dioxide. How animals take
in oxygen depends on their complexity and habitat. Many
animals breathe in oxygen from air or water using structures
such as lungs or gills, and have a blood system to carry the
oxygen to their cells.

Air sacs
connected
FLATWORM
to lungs
These simple animals have
neither a respiratory system
to take in oxygen nor a blood
system to carry it to their
cells. Instead, a flatworm
takes in oxygen and loses
carbon dioxide directly
through its surface. This is
possible because the
flatworm, being extremely
thin, possesses a very large
outer surface through which
oxygen can pass.

MOLLUSK FISH
How mollusks take in oxygen Red because of their rich blood
depends on their type and supply, a fish’s gills are located
habitat. Land snails, slugs, behind its mouth. The fish draws
and air-breathing pond water into its mouth, across
snails have a lung. Marine its gills, and back out again.
mollusks, including sea Dissolved oxygen passes
slugs and clams, use gills into the bloodstream and
to take in oxygen from circulates around the body.
Pond snail
the surrounding water, as
do octopuses and squid.

Goldfish
Newt
AMPHIBIAN tadpole
LARVA
This newt larva or
tadpole—like other young
Feathery
amphibians—depends on
external gills
feathery external gills to
extract oxygen from water. Flaplike
When it becomes an adult newt it operculum
will lose its gills and develop lungs. covers gills

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