Amphibians
What are some characteristics?
Characteristics
• Thin skin
• Must go to the water to
reproduce
• Egg layers
• Life cycle – eggs - tadpole to adult
• Large eyes
• 3 chambered heart
• Front /fore and hind
legs
• Diverse colors and
sizes
• Amphibians have survived for
hundreds of millions of years living in
places where there is fresh water.
• They are the only modern
descendants of an ancient group that
gave rise to all other land
vertebrates.
There are over 4,000 species of frogs!
What are amphibians?
• Means “double life”
• The larvae have gills and the adults have
lungs.
• Adults live in the water and land. They
breathe using both their lungs and skin.
What are Amphibians?
• They are vertebrates
• Skin is thin and moist, have mucus glands
• They lack scales and claws
Evolution of Amphibians
• The first amphibians
were probably lobed
finned fishes similar to
the modern coelacanth.
• Appeared in the
Devonian period
• They had the same
challenges are the
invertebrates did
Form and Function in Amphibians
Feeding: TADPOLES
1. Tadpoles filter feed or
are herbivores
2. They eat constantly
3. Their intestines break
down the cellulose
from the plants and
algae they eat
Form and Function in Amphibians
Feeding: ADULT FROGS
1. Adults are entirely
carnivores
2. They eat anything they
can catch and swallow
Digestion
Path of Food
Tongue
Mouth
Glottis
Esophagus
Stomach
Small Intestine
(liver, gall bladder, pancreas)
Large Intestine
Cloaca – a large muscular
cavity where the wastes,
urine and eggs or sperms
leave the frog’s body
Frog Teeth
Maxillary teeth – many
small sharp teeth on
the upper jaw only used
for holding.
Vomerine teeth – 2 of
them on the upper roof
of mouth, used for
holding only
Frog’s Tongue
• Very sticky!
• Long and can stretch
• Attached at the
front of the mouth
Respiration
Adult frogs –
respiration is with the
lungs and skin
The lungs are well
developed
Larvae – respiration is
with the gills and skin
Circulation
The frog heart has 3
chambers
Left Atrium
Right Atrium
One Ventricle
Excretion
Frogs have kidneys
that filter wastes
from the blood. The
excretory product of
the kidneys is urine.
It then travels
through tubes called
ureters into the
cloaca.
Reproduction
Frog eggs don’t have
shells and they tend to
dry out if they are not
kept moist. The females
lay eggs (about 200)
mostly in water.
The male frog fertilizes
them externally.
Most frogs abandon these
eggs to develop.
Guess the different stages…
Movement of Frogs
Larvae
Most amphibian larvae
move very much like
fish by wiggling their
bodies and using a
flattened tail for
propulsion.
Adult Frogs
Use their front and back
legs to move in a
variety of ways
Response
Frogs have well developed
nervous and sensory
systems.
Frog eyes are large and can
move around in their sockets
Nictitating membrane – a
movable membrane is
located inside the regular
eyelid which can also be
closed over the eye. This
enables them to respond to
moving objects. They don’t
see color.
Ecology of Frogs
Scientists are concerned about the
declining number of amphibians
especially frogs. Why is this happening?
What environmental threats?
global warming
decreasing habitat
depletion of the ozone layer
acid rain
water pollution
fungal infection
aquatic predators
increasing human
population