Essay, Research Paper: Frogs

Frogs

Frogs are amphibians in the order Anura. The order Anura is broken down into
twenty-two different families of frogs and toads. Although they belong to the same order,
frogs and toads are different in a lot of ways. Some of the more distinct differences are
their skin and where they live. Frogs usually have smooth, moist skin, and toads usually
have dry, warty-looking skin. Frogs spend most of their lives in or near water, and toads
spend more time on land. Amphibian means "double life". Frogs and toads each have
two parts to their lives: when they live on water and when they live on land.
A frog's life starts in the water when it is hatched from an egg as a tadpole. A
tadpole looks very different from an adult frog. A tadpole has a tail, no limbs, and
breathes through gills. After a while, the tadpole goes through a metamorphosis. During
the metamorphosis, the frog grows limbs, the tail disappears, it uses lungs to breathe, and
it doesn't have to live in water anymore. As a tadpole, the frog feeds mostly on
vegetation. The tadpoles has a small rasping mouth suited especially for scraping algae
from the bottom of ponds. Depending on the species, it can take a few weeks to a year or
more for the tadpoles to become fully grown. Not all frogs hatch as tadpoles though.
Some species of frogs hatch as froglets. Froglets look just like adult frogs, but a lot
smaller. Froglets don't go through a metamorphosis. Most species that hatch as froglets
are found in dry places. Frogs who live in dry places where rains are seasonal have to
grow up quickly because a tadpole will die if their temporary pond dries up.
Adult frogs can live in water or on land, but it always needs to be near water so
that its respiratory organs don't dry out. Frogs also need to be near water because most
species of frogs lay their eggs in the water. In most species, only male frogs croak. They
croak to attract female frogs, to display distress, and to warn away other male frogs from
their territory. Frogs reproduce by amplexus. During amplexus, the male frog holds on to
the female's back with specially adapted thumbs. Amplexus stimulates the female to
release eggs that the male then fertilizes. Not all of the eggs that are fertilized will end up
hatching though because they are not protected from predators and they are soft and can
be easily damaged. The only defense the eggs have is a jellylike coating that has a bad
taste. Depending on the species, the fertilized eggs will take two days to a month to
hatch. Most frogs live for about four to fifteen years.
Frogs eat a variety of foods when they are full grown. Mostly, adult frogs are
carnivorous. They typically worms, spiders, centipedes, and other insects. Frogs have a
tongue different from most animals. A frog's tongue is attached in the front and is sticky.
These differences give the frog an advantage when trying to catch its food. Aquatic frogs
also eat other frogs, small fish, and tadpoles. Some of the larger species, like the African
bullfrog, try to eat almost anything, including other frogs, mice, small snakes, and small
fish.
There are also a lot of animals that prey on frogs including alligators, snakes,
owls, raccoons, and herons. Frogs have a few ways of defense. One of the most obvious
ways is camouflage. The dorsal side of the frog's body is usually brown or green in color
so it will blend with the ground when seeing it from above. The ventral side of the frog's
body is light colored so that it blends with the sky when it's swimming. The coloring of
poisonous frogs acts as a warning sign. Poisonous frogs are very brightly colored so that
a predator will know it isn't safe to eat. Another way of defense for frogs is jumping.
Their powerful back legs let them escape quickly. Some frogs can jump up to twenty
times their own body length in one leap. Frogs often jump into ponds where they can hide
underwater from their predators. On land, frogs jump in random directions to confuse the
predator. A frog also has to protect itself from the climate because, like all amphibians,
they are cold-blooded. During the winter, frogs survive by burying themselves in mud and
hibernating. Their body functions slow down so they don't need much energy. When
hibernating in mud, frogs get air by absorbing it with their skin.
There are many characteristics unique to frogs. Some external features are the
bulging eyes and nostrils, the smooth, moist skin, external eardrums, and long back legs.
Frogs nostrils and eyes are specially designed so they see above water and breathe while
they are floating near the surface. Each eye is also covered by a nictitating membrane.
The nictitating membrane acts as a third eyelid and keeps the eyeball moistened. The
smooth, moist skin helps them from drying out. On the frog's skin there are mucus glands
that keep the frog's skin damp by secreting a slimy substance. Some frogs also secrete
poison through their skin. Frogs no real external ears. Instead, they have external
eardrums called tympanic membranes. There is a tympanic membrane located behind each
eye. A canal leading from the mouth to the tympanic membrane called the Eustachian
tube keeps equal air pressure on each side of the tympanic membrane. The inner ear is
located under the tympanic membrane. Frogs have long, muscular hind legs built
especially for jumping and swimming. Since jumping is a way of defense, there needs to
be a lot of strength in their legs. Swimming also requires strong legs, and because frogs
spend a lot of time in the water, the strength is necessary.
Other characteristics unique to frogs are mouth breathing and a three chambered
heart. To breathe through its mouth, the frog must first create a vacuum. It does that by
lowering the bottom of its shut mouth. Air moves into the mouth through the nostrils,
then the frog closes its nostrils and raises it's mouth. This forces air into the lungs. The
three chambers of a frog's heart are two atria and one ventricle. Blood coming from the
frog's body goes into the right atrium and blood coming from the lungs goes into the left
atrium. The oxygen-poor and the oxygen-rich blood both go to the single ventricle where
they mix and are sent to both the body and the lungs.
People have many uses for frogs. Frogs are used are used in education and
medicine for research and learning. They are also important in controlling insect pests.
Frogs feed on many species of insects, which greatly helps improve the quality of farm
crops and helps defend certain plant species.