Answer 1:
Good question! Frogs are great animals to
use in the study of embryology and
development, and they're especially
interesting because they're one of the only
vertebrates (animals with backbones, like us) to
go through a larval stage--the tadpole stage.
Different frog species develop at different
speeds, but I'll tell you about a species called
the African Clawed Frog, whose scientific name
is Xenopus laevis. This is the species that most
developmental biologists study.
Development begins when their eggs are
fertilized by sperm cells. About 10 hours after
that, the embryos go through gastrulation, which
is the formation of the mouth, gut, and anus.
About 8 hours after that, the embryos go through a
process called neurulation, which is the
formation of the brain and spinal cord. After
that, their bodies and tails start to take shape,
and in about 56 hours they become fully developed
tadpoles. At this point, it's been 74 hours since
fertilization, or just over three days.
Development from a tadpole to an adult frog
takes about a year. They're now able to reproduce,
which is when most scientists consider development
to be finished. Remember, though, that
different frog species might develop more
quickly or more slowly that the African Clawed
Frogs.
I hope that answers your question. Have fun
with your biology classes! | 
