Animal Life Cycles

Life Science - Middle School

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All animals (and all living things) have a life cycle. The adults reproduce - the male and female mate and the female grows the developing young inside her body for an amount of time. This is called gestation and can be just a few days (the frog) or up to two years (the African elephant). Some animals, like insects, reptiles and amphibians, lay eggs, while mammals have live young. Some animals, like many insects and amphibians, have life cycles with complex physical changes called a metamorphosis. While other animals like mammals and birds are born small and helpless, but with parental care will grow and develop into their adult form. Then they too can reproduce and the life cycle continues. Different animals have different kinds of life cycles. Even among insects there are two very different kinds of metamorphosis. Some insects, like grasshoppers, undergo incomplete metamorphosis, where the young nymphs hatch looking like tiny adults. They grow and periodically shed their hard outer exoskeleton, each new size called an instar. Most insects, however, go through a complete metamorphosis with new hatchlings called larvae that look completely different than adults. These soft-bodied young (caterpillars) have no exoskeleton so they can just feed and keep growing. When they reach a certain size, they finally form a protective cocoon or chrysalis and begin to change or pupate. During pupation their body breaks down and changes into their adult form. Then they break free of the cocoon and fly away. Mammals, including humans, go through changes as they age to adulthood too, but they are more gradual and don’t require a cocoon. Here are some illustrated examples of different animal life cycles and the changes they go through. Life Cycle of the Monarch Butterfly Life Cycle of the Bullfrog Life Cycle of the Loon Life Cycle of the Human egg hatching larva growing larva pupa in chrysalis adult hatching from chrysalis adult adult adults adult eggs eggs eggs hatching tadpoles growing limbs shrinking tail hatching egg hatchlings growing chicks young fledgling baby toddler child teenager (adolescent) Animal Life Cycles growing tadpoles
94-4037 All animals have a life cycle. Adults ____________________________ a male and female mate and the female grows developing young inside her body. This is called _______________________________ and can be just a few days (the frog) or up to two years (elephants). Some animals, like insects, reptiles and amphibians lay ___________ while mammals have _______________ young. Many insects and amphibians go through complex physical changes called _________________________________. Other animals like mammals and birds are born small and helpless, but with parental care will grow and develop into their adult form. Different animals have different kinds of life cycles. Even among insects there are two very different kinds of _______________________________. Some insects like grasshoppers undergo _______________________________ _______________________________, where the young __________________ hatch looking like tiny adults. They grow and shed their hard outer _____________________________, each new size called an ___________________. Most insects, however, go through a _______________________ _____________________________ with new hatchlings called ____________________ that look completely different than adults. These soft-bodied young (caterpillars) have no exoskeleton so they can just feed and keep growing. When they reach a certain size, they finally form a protective ________________________ or ________________________ and begin to change or _____________________. During _________________________ their body breaks down and changes into their adult form. Mammals, including humans, go through changes as they age to adulthood too, but they are more gradual and don’t require a ________________________. Here are some examples of different animal life cycles. Life Cycle of the Monarch Butterfly Life Cycle of the Bullfrog Life Cycle of the Loon Life Cycle of the Human egg hatching larva growing larva pupa in chrysalis adult hatching from chrysalis adult adult adults adult eggs eggs eggs hatching tadpoles growing limbs shrinking tail egg hatching hatchlings growing chicks young fledgling baby toddler child teenager (adolescent) growing tadpoles Animal Life Cycles