1. Amphibians

2. What is an amphibian?
Amphibians can be defined as vertebrates that are aquatic as larvae and terrestrial as adults, breathe with lungs as adults, have a moist skin that contains many glands, and lack scales and claws.
Keep in mind, there are always exceptions.

3. Figure 30–26 The Life Cycle of a Frog
Adult Frog
Adults are typically ready to breed in about one to two years.
Young Frog
Frog eggs are laid in water and
undergo external fertilization.
The eggs hatch into tadpoles a few days to several weeks later.
Fertilized Eggs
Tadpoles
Tadpoles gradually grow limbs, lose their tails and gills, and
become meat-eaters as they develop into terrestrial adults.

4. Nearly all must live in moist areas because
Aquatic larvae
Eggs do not have shells (could dry out)
Amphibian skin lacks protective covering that would prevent it from drying out
In most adults, the skin is used for respiration and must remain moist.

5. Evolution of Amphibians
First appeared around 360 mya (Devonian)
Bones became stronger permitting movement on land
Rib cage formed to protect internal organs
Ears were added to the lateral line system

6. Amphibians had very little competition for food and were very successful.
Carboniferous Period is sometimes called the age of amphibians.

8. Form and Function in Amphibians
Feeding
As larvae, most are filter feeders or herbivores
As adults, most are carnivorous
Food travels in the following order: mouth, esophagus, stomach, small intestine ( enzymes from liver, pancreas, and gall bladder), large intestine, colon

9. Respiration
Adults typically breathe using lungs, mouth cavities, and skin.
The skin is where most carbon dioxide is removed. And in salamanders and frogs, oxygen is also taken in by it.

10. Internal transport
Tadpoles have two-chambered hearts and a single loop system (heart, gills, rest of body, back to heart)
Adults have a three-chambered heart and a double loop system

11. Excretion
Kidneys eliminate wastes from the blood stream
Urine travels from the kidneys through the ureters to the cloaca, where it can be passed directly to the outside or stored in a small bladder