| A | B |
|---|
| bird | an endothermic vertebrate that has feathers and a four-chambered heart, and lays eggs |
| contour feather | a large feather that helps give shape to a bird's body |
| down feather | short, fluffy feathers that trap heat and keep a bird warm |
| insulator | a material that does not conduct heat well and thus helps to prevent heat from escaping |
| crop | a bird's internal storage tank that allows it to store food inside its body after swallowing |
| gizzard | a thick-walled, muscular part of a bird's stomach that squeezes and grinds partially digested food |
| lift | a upward force on a object that results from the difference in pressure between the upper and lower surfaces of the object |
| mammal | an endothermic vertebrate with a four-chambered heart, skin covered with fur or hair, and has young fed with milk from the mother's body |
| incisors | flat-edged teeth used to bite off and cut parts of food |
| canines | sharply pointed teeth that stab food and tear into it |
| premolars | teeth that, along with molars, grind and shred food into tiny bits |
| molars | teeth that, along with premolars, grind and shred food into tiny bits |
| diaphragm | a large, dome-shaped muscle that plays an important role in breathing |
| mammary gland | the organs that produce the milk with which mammals feed their young |
| monotreme | a mammal that lays eggs |
| marsupial | a mammal whose young are born alive at a early stage of development, and which usually continue to develop in a pouch on their mother's body |
| gestation period | the length of time between fertilization and birth of a mammal |
| placental mammal | a mammal that develops inside its mother's body until its body systems can function independently |
| placenta | a membrane that becomes the link between the developing embryo or fetus and the mother |
