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Unit 18: Biology Part 1 Page 27 of 60
Frogs can be characterized by long organism” for study in the
legs and the absence of a tail. laboratory because their larval
They spend their adulthood out of forms can be fairly easily
the water, breathing through manipulated and they generally
lungs. Frogs enter the water in the reproduce quickly.
adult stage only to reproduce.
Introduction to Reptiles
Frogs have elongated ankle bones,
and with their long legs, they are Reptiles don’t have the best
usually excellent jumpers. These reputation. Whether it’s a
amphibians also tend to have weak poisonous snake or a vicious
connective tissue, giving their skin crocodile, many people think of
a leathery, warty appearance. these animals in negative terms.
They also have three eyelids, As we will see, much of the
including a transparent eyelid reputation is undeserved, based on
specifically for protecting the eye misunderstandings of these
while in the larval stage, known in animals. Indeed, reptiles fill an
frogs as the tadpole stage. The important part of the ecosystems
other eyelids act as the eyelids do in which they live.
for many other terrestrial animals. Reptiles are spread out widely,
Frogs (believe it or not) are seen living on every continent except
as delicacies in many parts of the Antarctica. These vertebrates are
world, and are used as a source of characterized by breathing air,
food. They have also figured being ectothermic, being
prominently in stories and folklore. tetrapods (having four legs), and
The word salamander comes from being amniotes (meaning that
the word for “fire” because of the their embryos are surrounded in
fact that these amphibians often amniotic fluid). Most reptiles lay
live in old logs, and would come eggs, although some give birth to
out when there was a fire. This led live young. In all cases, the birth
some people to believe the fire was process is more similar to
creating the salamanders. mammals than it is to amphibians
Scientists view amphibians as or fish in terms of both the
excellent indicators of the health of nourishment and care that parents
an ecosystem because they are give the offspring.
generally are in the middle of the Lizards and snakes make up the
food web. Finally, amphibians largest order of the reptiles.
have been considered a “model Although we often think of them
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