Amphibians and Their Evolution

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10 Questions

What was a major modification required for vertebrates to move from water to land?

Changes in skin, breathing, and movement

What is a characteristic of amphibians?

They are ectothermic, or cold-blooded

What feature of frogs allows them to make sound?

A larynx, or voice box

What is a key difference between amphibians and reptiles?

Amphibians lay eggs in water, while reptiles produce amniotic eggs

What is the primary reason some amphibians evolved into reptiles?

To overcome resource limitations in aquatic environments

What is the primary function of the membrane in an amniotic egg?

To prevent moisture loss

What is a characteristic that reptiles have in common with amphibians?


Which reptiles have a four-chambered heart?

Crocodiles and alligators

What is the primary function of scales on reptiles' skin?

To prevent water loss

Where can reptiles be found?

In the ocean, freshwater, and on land

Study Notes


  • Modification to movement, breathing, and skin were necessary for vertebrates to transition from water to land
  • Amphibians are vertebrates that inhabit both freshwater and terrestrial environments
  • Examples of modern amphibians include frogs, salamanders, and caecilians
  • Amphibians are the first tetrapods, possessing four limbs
  • They are ectothermic, meaning their internal body temperature is the same as their environment
  • Amphibians have a complex circulatory system featuring a three-chambered heart
  • Frogs possess a larynx, enabling them to produce sound
  • Oxygen is absorbed through the skin in amphibians

Reproduction in Amphibians

  • Amphibians do not produce amniotic eggs
  • Eggs are laid in water to prevent desiccation
  • Early larvae stages (tadpoles) resemble fish, with gills, no legs, and a tail for swimming


  • The limited resources in aquatic environments likely led to the evolution of amphibians into reptiles
  • Reptiles are tetrapod vertebrates that produce amniotic eggs, enabling them to survive outside water
  • Examples of reptiles include crocodiles, alligators, lizards, snakes, and turtles

Amniotic Eggs

  • Amniotic eggs consist of a shell, membrane, and other structures that protect and nourish the embryo
  • The yolk provides a rich, fatty food source for the embryo
  • The amniotic membrane allows for gas exchange while preventing water loss

Reptile Structures

  • Reptiles have scales covering their skin to prevent water loss
  • They breathe air exclusively through their lungs (not skin)
  • Crocodiles and alligators possess a diaphragm, a large sheet of muscle controlling breathing
  • Reptiles are ectothermic, having the same body temperature as their environment
  • Most reptiles have a three-chambered heart, while crocodiles and alligators have a four-chambered heart
  • Reptiles inhabit ocean, freshwater, and land environments

Learn about the adaptations and characteristics of amphibians, including their movement, breathing, and skin modifications, as well as their classification as vertebrates.

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