Biology
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30-3 Amphibians
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30-3 Amphibians
What Is an Amphibian?
What is an amphibian?
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30-3 Amphibians
What Is an Amphibian?
What Is an Amphibian?
An amphibian is a vertebrate that, with
some exceptions:
• lives in water as a larva and on land as
an adult
• breathes with lungs as an adult
• has moist skin that contains mucous
glands
• lacks scales and claws
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30-3 Amphibians
Evolution of Amphibians
How are amphibians adapted for life on
land?
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30-3 Amphibians
Evolution of Amphibians
Evolution of Amphibians
The first amphibians appeared in the late
Devonian Period, about 360 million years ago.
The transition from water to land required that
the terrestrial vertebrates had to:
• breathe air,
• protect themselves and their eggs from
drying out, and
• support themselves against the pull of
gravity.
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30-3 Amphibians
Evolution of Amphibians
Early amphibians evolved several
adaptations that helped them live at least
part of their lives out of water.
Bones in the limbs and limb girdles of
amphibians became stronger, permitting
more efficient movement.
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Evolution of Amphibians
Lungs and breathing tubes enabled
amphibians to breathe air.
The sternum formed a bony shield to
support and protect internal organs,
especially the lungs.
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30-3 Amphibians
Evolution of Amphibians
Amphibian Adaptations
Lungs
Pelvic Girdle
Leg Bones:
The legs of a land
vertebrate must be
strong enough to hold
its weight.
Skin: The skin and the lining of
the mouth cavity of many adult
amphibians are thin and richly
supplied with blood vessels.
Watery mucus is secreted by
glands in the skin.
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30-3 Amphibians
Evolution of Amphibians
In many adult amphibians, the internal surfaces of the
lungs are richly supplied with blood vessels and folds
that increase surface area.
Lungs
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30-3 Amphibians
Form and Function in Amphibians
Form and Function in Amphibians
The class Amphibia is relatively small and diverse.
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30-3 Amphibians
Form and Function in Amphibians
Feeding
Tadpoles are typically filter feeders or herbivores
that graze on algae.
Their intestines help break down hard-to-digest
plant material and are usually filled with food.
The feeding apparatus and digestive tract of adults
are meat-eating structures.
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30-3 Amphibians
Form and Function in Amphibians
Frog Anatomy
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Form and Function in Amphibians
Adult amphibians are almost entirely carnivorous.
Many salamanders and frogs have long, sticky
tongues specialized to capture insects.
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Form and Function in Amphibians
Mouth
In a frog’s digestive
system, food slides down
the esophagus into the
stomach.
Esophagus
Stomach
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Form and Function in Amphibians
The breakdown of food
begins in the stomach
and continues in the
small intestine.
Small intestine
Stomach
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30-3 Amphibians
Form and Function in Amphibians
The liver, pancreas, and
gallbladder secrete
substances that aid in Gallbladder
digestion.
Liver
Pancreas
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Form and Function in Amphibians
At the end of the large
intestine is a muscular
cavity called the cloaca,
through which digestive
wastes, urine, and eggs
or sperm leave the body.
Large
intestine
(colon)
Cloaca
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30-3 Amphibians
Form and Function in Amphibians
Respiration
In most larval amphibians, gas exchange occurs
through the skin and the gills.
Adult amphibians typically respire using lungs, but
some gas exchange occurs through the skin and
the lining of the mouth.
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30-3 Amphibians
Form and Function in Amphibians
Circulation
In frogs and other adult amphibians, the circulatory
system forms a double loop.
The first loop carries oxygen-poor blood from the
heart to the lungs and skin, and takes oxygen-rich
blood from the lungs and skin back to the heart.
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Form and Function in Amphibians
The second loop transports oxygen-rich blood from
the heart to the rest of the body, and carries oxygenpoor blood from the body back to the heart.
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Amphibian
Circulation and
Excretion
Form and Function in Amphibians
Heart
Lung
Kidney
Ureter
Urinary
bladder
Cloaca
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30-3 Amphibians
Form and Function in Amphibians
The amphibian heart has three separate chambers:
•left atrium
•right atrium
•ventricle
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30-3 Amphibians
Form and Function in Amphibians
To body,
lungs and
skin
Amphibian
Heart
From
Body
To body,
lungs and
skin
From
Lungs
Left
atrium
Right
atrium
Ventricle
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Form and Function in Amphibians
Excretion
Amphibians have kidneys that filter wastes from
the blood.
Urine travels through tubes called ureters into the
cloaca.
Urine is then passed directly to the outside, or
temporarily stored in a small urinary bladder just
above the cloaca.
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Form and Function in Amphibians
Reproduction
In most species of amphibians, the female lays
eggs in water, then the male fertilizes them
externally.
In a few species, including most salamanders,
eggs are fertilized internally.
After fertilization, frog eggs are encased in a sticky,
transparent jelly.
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30-3 Amphibians
Form and Function in Amphibians
The jelly attaches the egg mass to underwater plants
and makes the eggs difficult for predators to grasp.
The yolks of the eggs nourish the embryos.
Most amphibians abandon their eggs after they lay
them.
A few amphibians take care of both eggs and young.
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30-3 Amphibians
Form and Function in Amphibians
Frog Metamorphosis
Adult
Frog
Fertilized
eggs
Young
Frog
Tadpoles
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Form and Function in Amphibians
Adults are typically ready to breed in about one to
two years.
Frog eggs are laid in water and undergo external
fertilization.
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Form and Function in Amphibians
The fertilized eggs hatch into tadpoles a few days
to several weeks later.
Fertilized eggs
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Tadpoles gradually
grow limbs, lose their
tails and gills, and
become meat-eaters
as they develop into
terrestrial adults.
Form and Function in Amphibians
Young frog
Tadpole
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Form and Function in Amphibians
Movement
Amphibian larvae move by wiggling their bodies
and using a flattened tail for propulsion.
Adult salamanders walk or run.
Frogs and toads, have well-developed hind limbs
that enable them to jump long distances.
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Form and Function in Amphibians
Response
Amphibians have well-developed nervous and
sensory systems.
An amphibian's eyes are protected from damage
and kept moist by a transparent nictitating
membrane.
This membrane is located inside the regular eyelid
and can be closed over the eye.
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Form and Function in Amphibians
Amphibians hear through tympanic membranes, or
eardrums, located on each side of the head.
Many amphibian larvae and adults have lateral line
systems that detect water movement.
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Form and Function in Amphibians
Frog’s Sense Organs
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30-3 Amphibians
Groups of Amphibians
What are the main groups of living
amphibians?
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Groups of Amphibians
Groups of Amphibians
The three groups of amphibians alive
today are:
• salamanders
• frogs and toads
• caecilians
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Groups of Amphibians
Salamanders
Salamanders and newts have long bodies and
tails.
Most have four legs.
Both adults and larvae are carnivores.
Adults usually live in moist woods, where they
tunnel under rocks and rotting logs.
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Groups of Amphibians
Frogs and Toads
Frogs and toads have the ability to jump.
Frogs tend to have long legs and make lengthy
jumps.
Toads have relatively short legs and are limited to
short hops.
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Groups of Amphibians
Frogs are generally more closely tied to water than
toads.
Toads often live in moist woods and even in deserts.
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Groups of Amphibians
Caecilians
Caecilians are legless animals that live in water or
burrow in moist soil or sediment.
Caecilians feed on small invertebrates such as
termites.
Many have fishlike scales embedded in their skin.
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30-3
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30-3
The word amphibian refers to the ability to
a. live in hot climates.
b. live in wet places.
c. live both in water and on land.
d. live in cold and hot climates.
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30-3
Fossil evidence indicates the first land
amphibians appeared during the
a. Jurassic Period.
b. Devonian Period.
c. Cambrian Era.
d. Cretaceous Era.
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30-3
In a larval amphibian, gas exchange occurs
through
a. the skin only.
b. both the skin and the gills.
c. the gills only.
d. a lung.
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30-3
The tympanic membrane in a frog enables it to
a. hear.
b. see.
c. smell.
d. taste.
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30-3
Which of the following is a group of amphibians
living on the Earth today?
a. crocodiles
b. snakes
c. salamanders
d. lizards
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