Chapter 28 Section 3_Amphibians (1)

Introduction to Amphibians

• Most amphibians begin life as aquatic organisms.

• Transition to land occurs as adults.

Essential Questions

• What adaptations were crucial for animals transitioning to land?

• What are the defining characteristics of amphibians?

• How do different orders of amphibians vary?

Vocabulary Review

• Metamorphosis: process of transformation from larva to adult.

• Cloaca: common opening for excretion and reproduction.

• Nictitating Membrane: protective transparent eyelid.

• Tympanic Membrane: eardrum, involved in hearing.

• Ectotherm: organism that relies on external sources for body heat.

Evolution of Tetrapods

• Tetrapods: four-legged vertebrates evolved ~360 million years ago.

• Faced significant physical challenges moving from water to land.

Adaptations for Life on Land

• Life conditions on land differ drastically from aquatic environments.

• Notable adaptations for life on land included:

  • Changes in breathing.

  • Changes in locomotion.

  • Changes in reproduction.

Land Habitats for Animals

• Diverse land habitats include:

  • Tropical rain forests

  • Temperate forests

  • Grasslands

  • Deserts

  • Taiga

  • Tundra

• Appropriate adaptations enable survival in these varying ecosystems.

Characteristics of Amphibians

• Amphibians start life as aquatic organisms and undergo metamorphosis:

  • Tadpoles develop limbs.

  • Lungs replace gills.

  • Tails shorten.

• Transition into adult form is evident in frogs.

Key Features

• Typical anatomy of amphibians:

  • Four limbs

  • Moist skin without scales

  • Double-loop circulatory system

  • Aquatic larvae

• Respiration occurs through skin and lungs.

Feeding and Digestive Processes

• Dining habits:

  • Frog larvae (herbivores) vs. salamander larvae (carnivores).

  • Both groups become predators as adults, feeding on invertebrates and small vertebrates.

• Different feeding mechanisms:

  • Salamanders catch prey using jaws.

  • Frogs use long, sticky tongues for capturing aerial prey.

Digestive System Overview

• Digestive process:

  • Food travels from mouth to esophagus to stomach (digestion starts).

  • Moves to the small intestine for enzyme action from the pancreas.

  • Nutrients are absorbed into the bloodstream.

  • Waste is processed in the large intestine before exiting via the cloaca.

Excretory System

• Waste elimination:

  • Kidneys filter blood waste.

  • Aquatic amphibians excrete ammonia; terrestrial ones excrete urea.

  • Urea is less toxic and is stored until expelled.

Gas Exchange Mechanisms

• Gas exchange methods:

  • Larval stage: skin and gills.

  • Adult stage: lungs, moist skin, and mouth cavities used for breathing.

Circulatory System Function

• Double-loop circulatory system:

  • First loop: oxygen-poor blood circulates to lungs and skin for oxygen uptake.

  • Oxygen-rich blood returns to the heart.

Circulation and Heart Anatomy

• Second loop:

  • Oxygen-rich blood circulates from the heart to body tissues and cells.

• Heart structure:

  • Three chambers: right atrium (oxygen-poor), left atrium (oxygen-rich), ventricle.

Sensory Adaptations

• Senses and survival:

  • Vision aids in prey capture and avoiding predators.

  • Frogs have nictitating membranes for eye protection.

  • Tympanic membranes detect sound.

Thermoregulation

• Ectothermic behavior:

  • Body temperature is regulated via environmental heat sourcing.

Reproductive Strategies

• Reproduction:

  • Predominantly external fertilization.

  • Shell-less eggs require water for laying and fertilization.

  • Tadpoles undergo metamorphosis to mature forms.

Classifying Amphibians

• Classification:

  • Order Anura: frogs and toads.

  • Order Caudata: salamanders and newts.

  • Order Gymnophiona: caecilians.

Frogs vs. Toads

• Distinction features:

  • Frogs: longer legs, smooth skin, need more water for reproduction.

  • Toads: bumpy skin, glands for defensive poison, live farther from water.

Salamanders and Newts

• Typical attributes:

  • Long, slim bodies; moist skin; lay eggs in water.

  • Larval forms resemble adults.

  • Prefer moist habitats and feed on invertebrates.

  • Newts remain aquatic throughout life.

Unique Caecilians

• Characteristics:

  • Legless, resembling worms, burrow in soil.

  • Limited vision due to skin covering eyes.

  • Internal fertilization and moisture-needed egg laying.

  • Preferred habitat: tropical forests.

Recap of Essential Questions and Vocabulary

• Recap key concepts:

  • Adaptations for land transition.

  • General characteristics of amphibians.

  • Distinctions between amphibian orders.

• Vocabulary:

  • Cloaca, Nictitating membrane, Tympanic membrane, Ectotherm.