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Chapter 40 Amphibians

Table of Contents

Section 1 Origin and Evolution of Amphibians

Section 2 Characteristics of Amphibians

Section 3 Reproduction in Amphibians



Chapter 40

Section 1 Origin and Evolution of

Amphibians

Objectives

• Describe the three preadaptations involved in the transition from aquatic to terrestrial life.

• Describe two similarities between amphibians and lobe-finned fishes.

• List five characteristics of living amphibians.

• Name the three orders of living amphibians, and give an example of each.



Chapter 40


Amphibians

Adaptation to Land

• Preadaptations are adaptations in an ancestral group that allow a shift to new functions which are later favored by natural selection.

Lobe-finned fishes had several preadaptations that allowed them to transition to life on land.

• bone structure

• pouches in digestive tracts for gas exchange

• nostrils

• higher metabolism

• efficient hearts



Chapter 40

From Fin to Limb


Amphibians



Chapter 40


Amphibians

Adaptation to Land, continued

Characteristics of Early Amphibians

Amphibians and lobe-finned fishes share many anatomical similarities, including:

• similar skull

• similar vertebral column

• similar bone structure in fins and limbs

• early amphibians had a large tail fin and lateral line canals



Chapter 40


Amphibians

Characteristics of Early Amphibians



Chapter 40


Amphibians


Diversification of Amphibians

• About 300 million years ago amphibians split into two main evolutionary lines.

• One line included ancestors of reptiles, the other line included the ancestors of modern amphibians.



Chapter 40


Amphibians


Diversification of Amphibians

Today there are about 4,500 species of amphibians belonging to three orders:

• Anura - includes frogs and toads

• Caudata - includes salamanders and newts

• Gymnophiona - includes caecilians (legless tropical amphibians)



Chapter 40


Amphibians

Modern Amphibians

Modern amphibians share several key characteristics

• Most change from an aquatic larval stage to a terrestrial adult form, in a transformation called metamorphosis.

• Most have moist, thin skin with no scales.

• Feet, if present, lack claws and often are webbed.

• Most use gills, lungs, and skin in respiration.

• Eggs lack multicellular membranes or shells, are usually laid in water, and are usually fertilized externally.



Chapter 40


Amphibians

Characteristics of Amphibians



Chapter 40


Amphibians

Modern Amphibians, continued

Order Anura

• Order includes frogs and toads.

• Members may be fully aquatic, fully terrestrial, or amphibious.

• Most reproduce in water, laying eggs that hatch into swimming larvae called tadpoles.

• Larvae are herbivores. Adults are carnivorous and will eat any animal they can capture.



Chapter 40


Amphibians


Order Caudata

• Includes salamanders (may also be called newts).

• Members may be fully aquatic, fully terrestrial, or amphibious.

• Many reproduce in water. Some reproduce on land, with no swimming larval stage.

• Larvae and adults are carnivorous.

• Some have no lungs, and respire through their skin only.



Chapter 40


Amphibians


Order Gymnophiona

• Includes caecilians (legless amphibians that resemble small snakes).

• Most are burrowing. They have small eyes beneath skin or bone, and are often blind.

• All are carnivorous.

• All are thought to have internal fertilization.

• Some lay eggs which the female guards, others develop inside the female.



Chapter 40


Amphibians

Phylogenetic Diagram of Amphibians



Chapter 40


Amphibians

Types of Amphibians



Chapter 40

Section 2 Characteristics of

Amphibians

Objectives

• Relate the structure of amphibian skin to the types of habitats in which amphibians can survive.

• Identify three adaptations for life on land shown by the skeleton of a frog.

• Sequence the flow of blood through an amphibian’s heart.

• Describe how a frog fills its lungs with air.

• Describe the digestive and excretory systems of amphibians.

• Discuss an amphibian’s nervous system.



Chapter 40


Amphibians

Skin

Amphibian skin serves two important functions:

• Respiration - The skin is permeable to gases and water. Mucous glands secrete a lubricant that keeps the skin moist in air.

• Protection - The skin protects amphibians from infection and secretes a foul-tasting or poisonous mucus that protects amphibians from predators.



Chapter 40


Amphibians

External Structure of a Frog



Chapter 40


Amphibians

Skeleton

A strong skeleton supports the body of amphibians against the force of gravity.

• Vertebrae interlock to form a strong, rigid structure.

• Strong limbs assist with standing and walking.

• Pectoral and pelvic girdles transfer weight to the limbs.

• Skeletons of frogs are specialized for jumping and landing.



Chapter 40


Amphibians

Skeleton, continued

• Fused bones add strength to the forelimbs and hind limbs.

• Thick arm bones and pectoral girdle absorb shock of landing.

• Long hind legs allow frogs to jump farther.

• Lengthened pelvic girdle and fused vertebrae add support.



Chapter 40


Amphibians

Circulatory System

The circulatory system is divided into two loops.

• Pulmonary circulation - carries deoxygenated blood from the heart to the lungs and back to the heart.

• Systemic circulation - carries oxygenated blood from the heart to the body and back to the heart.



Chapter 40


Amphibians

Circulatory System, continued

Three chambered heart:



Chapter 40


Amphibians

Amphibian Heart Structure



Chapter 40


Amphibians

Frog Heart and Double-Loop Circulation



Chapter 40


Amphibians

Respiration

Amphibians use two forms of respiration

• Pulmonary respiration - respiration through the lungs

• Cutaneous respiration - respiration through the skin



Chapter 40


Amphibians

Respiration, continued

Amphibians use positive pressure breathing, shown below.



Chapter 40


Amphibians

Amphibian Lung Structure



Chapter 40


Amphibians

Respiration in Amphibians



Chapter 40


Amphibians

Digestive System

• Includes the pharynx, esophagus, stomach, liver, gallbladder, small intestine, large intestine, and cloaca.

• The upper part of the small intestine is called the duodenum.

• The coiled middle portion of the small intestine is the ileum.

• A membrane that holds the small intestine in place is called the mesentery.

• Waste materials are stored in the cloaca and exit the body through the vent.



Chapter 40


Amphibians

Digestive System, continued

Accessory Glands

• The liver produces bile, which is stored in the gallbladder and helps break down fat.

• The pancreas secretes enzymes that help break down food into particles that can be absorbed by the blood.



Chapter 40


Amphibians

Internal Structure of a Frog



Chapter 40


Amphibians

Excretory System

• The kidneys are the primary excretory organ, and filter nitrogenous wastes from the blood.

• Wastes combined with water are known as urine.

• Urine flows from the kidneys to the cloaca and then to the urinary bladder, which branches off the cloaca.

• Nitrogenous wastes are converted from ammonia to urea, which is highly concentrated and helps conserve water.



Chapter 40


Amphibians

Nervous System

• The olfactory lobes are larger in amphibians than in fish.

• The cerebrum is responsible for behavior and learning.

• The optic lobes process information from the eyes.

• The cerebellum is responsible for muscular coordination.

• The medulla oblongata controls heart rate and respiration rate.



Chapter 40


Amphibians

Nervous System

Sense Organs -

• Larvae have a lateral line, most adults do not.

• The eyes are covered by a nictitating membrane, a transparent moveable membrane that protects the eye.

• Sound is detected by the inner ear.

•

Sounds are transmitted to the inner ear by the tympanic membrane, or eardrum, and the columella, a small bone that extends between the tympanic membrane and the inner ear.



Chapter 40


Amphibians

Anatomy of a Frog



Chapter 40


Amphibians

Anatomy of a Frog (part 2)



Chapter 40

Section 3 Reproduction in

Amphibians

Objectives

• Explain how a male frog attracts a female of the same species.

• Discuss the reproductive system of a frog.

• Describe the life cycle of a frog.

• Describe the changes that occur during metamorphosis in frogs.

• Identify two examples of parental care in amphibians.



Chapter 40


Amphibians

Courtship and Fertilization

• Males attract females with a mating call.

• Females only respond to males of the same species.

• The male clings to the female in an embrace called amplexus.

• Eggs and sperm are released into the water.

• Fertilization is external.



Chapter 40


Amphibians

Courtship and Fertilization, continued

Reproductive system

• Male - includes two bean-shaped testes located near the kidneys that produce sperm during the breeding season.

• Female - includes a pair of large ovaries containing thousands of tiny immature eggs.

During the breeding season the eggs mature.



Chapter 40


Amphibians

Life Cycle

• When the eggs hatch, a tadpole is released.

• The tadpole grows and slowly changes from an aquatic larva into an adult in a process called metamorphosis.

• Metamorphosis is controlled by a hormone called thyroxine.

• Some amphibians do not produce thyroxine and remain in the larval stage their entire life.

• Some amphibians do not have a larval stage and hatch from the egg as small versions of the adult.



Chapter 40

Life Cycle of a Frog


Amphibians



Chapter 40


Amphibians

Amphibian Life Cycle



Chapter 40


Amphibians

Parental Care

Parental care increases the likelihood that the offspring will survive.

• Some species guard their eggs until they hatch.

• Some species sit on their eggs to prevent them from drying out.

• The male Darwin’s frog carries the eggs in his vocal sacs until the larvae finish metamorphosis.

• Female gastric brooding frogs swallow their eggs and the larvae mature in the stomach.



Chapter 40 Standardized Test Prep

Multiple Choice

1. The forelimbs of vertebrates evolved from which structures in lobe-finned fishes?

A. anal fin

B. pelvic fin

C. pectoral fins

D. pectoral girdle




Multiple Choice

1. The forelimbs of vertebrates evolved from which structures in lobe-finned fishes?

A. anal fin

B. pelvic fin

C. pectoral fins

D. pectoral girdle




Multiple Choice, continued

2. Amphibians must lay eggs in water primarily for what reason?

F. The eggs are not laid in nests.

G. The eggs need oxygen from water.

H. The eggs need protection from predators.

J. The eggs do not have multicellular membranes and a shell.





2. Amphibians must lay eggs in water primarily for what reason?

F. The eggs are not laid in nests.

G. The eggs need oxygen from water.

H. The eggs need protection from predators.

J. The eggs do not have multicellular membranes and a shell.




Multiple Choice

3. Metamorphosis must take place before amphibians are able to do what?

A. swim

B. live on land

C. respire with gills

D. feed themselves




Multiple Choice

3. Metamorphosis must take place before amphibians are able to do what?

A. swim

B. live on land

C. respire with gills

D. feed themselves





The figure below shows a longitudinal section, ventral view, of a frog heart. Use the figure below to answer question 4.





4. Identify the source of blood flow in the section of the heart labeled 1.

F. the body

G. the aorta

H. the lungs

J. both lungs and body





4. Identify the source of blood flow in the section of the heart labeled 1.

F. the body

G. the aorta

H. the lungs

J. both lungs and body




Multiple Choice

5. Anura : frogs :: Gymnophiona :

A. toads

B. newts

C. caecilians

D. salamanders




Multiple Choice

5. Anura : frogs :: Gymnophiona :

A. toads

B. newts

C. caecilians

D. salamanders





The figure below shows an artist’s rendering of

Ichthyostega. Use the figure to answer the question that follows.





6. Ichthyostega is an early amphibian. Which of the following characteristics is most likely to help it live on land?

F. fishlike tail

G. seven-toed feet

H. four strong limbs

J. lateral-line canals on the head





6. Ichthyostega is an early amphibian. Which of the following characteristics is most likely to help it live on land?

F. fishlike tail

G. seven-toed feet

H. four strong limbs

J. lateral-line canals on the head




Short Response

Modern amphibians are a diverse group, but they do have some common characteristics.

Describe five key characteristics shared by modern amphibians.




Short Response, continued

Modern amphibians are a diverse group, but they do have some common characteristics.

Describe five key characteristics shared by modern amphibians.

Answer: Metamorphosis from larva to adult; moist, thin skin; clawless feet; respiration with lungs, skin, and gills; shell-less eggs




Extended Response

Base your answers to parts A & B on the information below.

Frogs breathe by a positive pressure system.

Part A Describe how frogs move air into their lungs.

Which part of inhaling is “positive pressure?”

Part B Describe how frogs move air out of their lungs and into the atmosphere.




Extended Response, continued

Answer:

Part A The mouth floor drops, sucking air in.

The nostrils seal and the mouth floor lifts

(positive pressure), which forces air into the lungs.

Part B: The body wall muscles and lung elasticity force lung air into the mouth, which makes the floor drop. The floor then lifts to force air out of nostrils.



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