Amphibians
Amphibians are cold-blooded vertebrates (their body temperature changes with the environment).
They live both in water and on land during different stages of their life.
Examples: frogs, toads, salamanders, newts.
Features of Amphibians:
Skin: Moist, thin, and soft; used for breathing (through skin) and sometimes protection.
Respiration: Can breathe through gills (as young tadpoles) and lungs (as adults).
Reproduction: Usually lay eggs in water, eggs do not have hard shells.
Metamorphosis: Most amphibians go through metamorphosis, e.g., tadpole → frog.
Limbs: Usually have four limbs (except some like caecilians, which are limbless).
Life Cycle (Example: Frog):
Egg → Tadpole → Tadpole with legs → Froglet → Adult Frog
Young amphibians live in water, adults live on land but often return to water to reproduce.
Circulation:
Amphibians have a three-chambered heart: 2 atria + 1 ventricle.
Blood mixes partially (not fully separated like in mammals), which is enough for their cold-blooded metabolism.
Interesting Facts:
Amphibians are indicator species: their presence shows a healthy environment.
They can absorb water through their skin and usually don’t drink like mammals.
Many are endangered due to pollution, habitat loss, and climate change because their skin easily absorbs things.