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Terms and definitions for Chapter A2

backbone

the main bone, made up of many small bones joined together, that runs along the middle of the back in some animals

exoskeleton

a hard outer covering that supports and protects some animals without backbones

molt

to shed an animal's outer covering

gills

organs for breathing found in fish and amphibians

amphibian

one of a large group of animals with backbones that live part of their lives in water and part on land

reptile

an animal with a backbone that has dry, scaly skin

mammal

an animal with a backbone that usually has hair on its body and feeds milk to its young

reflex

a simple, automatic behavior

stimulus

the cause of a behavior

response

a behavior caused by a stimulus

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