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19.4: Reptiles

Difficulty Level: At Grade Created by: CK-12

Lesson 19.4: True or False

Name___________________ Class______________ Date________

Write true if the statement is true or false if the statement is false.

_____ 1. Reptiles include crocodiles, alligators, lizards, turtles, and all snakes except water snakes.

_____ 2. Reptiles are tetrapod vertebrates that produce amniotic eggs.

_____ 3. Reptile skin is covered with scales, which keeps the skin moist.

_____ 4. On land, reptiles breathe air through their lungs, and in the water, they breath using their gills.

_____ 5. It is possible for some reptiles to go weeks without eating.

_____ 6. Snakes smell using their tongue.

_____ 7. All reptiles have a three-chambered heart.

_____ 8. Like the amphibian tadpole, the reptilian larval stage also resembles a fish.

_____ 9. The shell, membranes, and other structures of the reptilian amniotic egg protect and nourish the embryo.

_____ 10. Some reptiles are at the top of the food chain - they ate the top predators in their ecosystems.

_____ 11. Alligators replace their teeth throughout their life.

_____ 12. Turtles are the least specialized of all living reptiles.

_____ 13. Snakes can swallow large prey whole.

_____ 14. Small crocodiles were early ancestors of most reptiles.

_____ 15. Crocodiles and alligators use a diaphragm to control their breathing, just like humans.

Lesson 19.4: Critical Reading

Name___________________ Class______________ Date________

Read these passages from the text and answer the questions that follow.

Structure and Function in Reptiles

Reptiles have several adaptations for living on dry land that amphibians lack. For example, the skin of most reptiles is covered with scales. The scales are made of very tough keratin, and they protect reptiles from injury and also prevent them from losing water.

Reptile Respiration

The scales of reptiles prevent them from absorbing oxygen through their skin, as amphibians can. Instead, reptiles breathe air only through their lungs. However, their lungs are more efficient than the lungs of amphibians, with more surface area for gas exchange. This is another important reptile adaptation for life on land.

Reptiles have various ways of moving air into and out of their lungs. Lizards and snakes use muscles of the chest wall for this purpose. These are the same muscles used for running, so lizards have to hold their breath when they run. Crocodiles and alligators have a large sheet of muscle below the lungs, called a diaphragm, that controls their breathing. This is a structure found also in mammals.

Ectothermy in Reptiles

Like amphibians, reptiles are ectotherms with a slow metabolic rate. Their metabolism doesn’t generate enough energy to keep their body temperature stable. Instead, reptiles regulate their body temperature through their behavior. For example, the crocodile in the figure below is soaking up heat from the environment by basking in the sun. Because of their ectothermy, reptiles can get by with as little as one tenth the food needed by endotherms, such as mammals. Some species of reptiles can go several weeks between meals.

Heat Transfer to an Ectothermic Reptile. This crocodile is being warmed by the environment in three ways. Heat is radiating directly from the sun to the animal’s back. Heat is also being conducted to the animal from the rocks it rests on. In addition, convection currents are carrying warm air from surrounding rocks to the animal’s body. (Image courtesy of wildxplorer and under the Creative Commons license CC-BY 2.0. Text added by CK-12 Foundation.)

Other Reptile Structures

Like amphibians, most reptiles have a heart with three chambers, although crocodiles and alligators have a four-chambered heart like birds and mammals. The reptile brain is also similar in size to the amphibian brain, taking into account overall body size. However, the parts of the reptile brain that control the senses and learned behavior are larger than in amphibians.

Most reptiles have good eyesight and a keen sense of smell. Snakes smell scents in the air using their forked tongue. This helps them locate prey. Some snakes have heat-sensing organs on their head that help them find endothermic prey, such as small mammals and birds.


1. Describe the skin of reptiles.

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2. How do reptiles breathe?

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3. “Reptiles are ectotherms.” What does this mean?

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4. How can reptiles heat their bodies?

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5. Describe reptilian senses.

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Lesson 19.4: Multiple Choice

Name___________________ Class______________ Date________

Circle the letter of the correct choice.

  1. Reptiles include which of the following? (1) crocodiles, (2) lizards, (3) snakes, (4) turtles.
    1. 1 and 2
    2. 3 and 4
    3. 1, 2, and 3
    4. 1, 2, 3, and 4
  2. Adaptations of reptiles for living on land include
    1. sense organs to smell and taste chemicals.
    2. a relatively complex circulatory system with a three-chambered heart.
    3. skin of most reptiles is covered with scales made of very tough keratin.
    4. all of the above.
  3. Reptiles breath air
    1. only through their lungs.
    2. through their skin.
    3. through both the skin and lungs, like amphibians.
    4. with gills as larvae.
  4. Reptiles are ectotherms. This means
    1. they warm their bodies through their behavior.
    2. they cannot use metabolism to generate heat.
    3. they need less food then mammals to survive.
    4. all of the above.
  5. There are four orders of reptiles. They are the
    1. Crocodilia, Sphenodontia, Squamata, and Testudines.
    2. Crocodilia, Alligatoria, Squamata, and Testudines.
    3. Crocodiles, Lizards, Snakes, and Turtles.
    4. Alligatoria, Sphenodontia, Squamata, and Testudines.
  6. The reptile amniotic egg
    1. protect and nourish the embryo during development.
    2. keeps the embryo moist and safe while it grows and develops.
    3. provides the embryo with a rich, fatty food source.
    4. all of the above
  7. Characteristics of the Crocodilia order include
    1. permanent teeth.
    2. a three-chambered heart.
    3. four sprawling legs that can be used to gallop.
    4. none of the above.
  8. Which statement about reptilian evolution is correct? (1) Reptiles, dinosaurs, and birds all developed from sauropsids. (2) Sauropsids evolved into dinosaurs. (3) Dinosaurs evolved from reptiles. (4) Lizards and snakes were the last reptiles to evolve.
    1. 1 and 2
    2. 1, 2, and 3
    3. 1, 2, and 4
    4. 1, 2, 3, and 4

Lesson 19.4: Vocabulary I

Name___________________ Class______________ Date________

Match the vocabulary word with the proper definition.


_____ 1. the amniotes that evolved into reptiles, dinosaurs, and birds

_____ 2. the amniotes that eventually gave rise to mammals

_____ 3. the least specialized of all living reptiles

_____ 4. have four sprawling legs that can be used to gallop

_____ 5. protect and nourish the embryo; keeps the embryo moist and safe while it grows and develops

_____ 6. Age of the Dinosaurs

_____ 7. a large sheet of muscle below the lungs that controls their breathing

_____ 8. have a hard shell covering most of their body

_____ 9. lizards and snakes

_____ 10. consists of all amniotes except birds and mammals


a. amniotic eggs

b. Crocodilia

c. diaphragm

d. Mesozoic Era

e. reptiles

f. sauropsid

g. Sphenodontia

h. Squamata

i. synapsid

j. Testudines

Lesson 19.4: Vocabulary II

Name___________________ Class______________ Date________

Fill in the blank with the appropriate term.

1. Large reptiles, such as crocodilians, have powerful ____________ that can crush bones and even turtle shells.

2. By the middle of the Triassic about 225 million years ago, sauropsids had evolved into ____________.

3. A snake flicks its ____________ in and out to capture scent molecules in the air.

4. Sauropsids were amniotes that evolved into reptiles, dinosaurs, and ____________.

5. Reptiles are ____________, unable to generate their own heat, so they have a slow metabolic rate.

6. Reptiles produce amniotic ____________.

7. Crocodiles and alligators have a ____________, a large sheet of muscle below the lungs.

8. Crocodiles and alligators have a four-chambered ____________ like birds and mammals.

9. The scales of reptiles prevent them from losing ____________.

10. Because of their ____________, reptiles can breathe air only through their lungs.

11. Testudines have a hard ____________ covering most of their body.

12. The shell, membranes, and other structures of an amniotic egg protect and nourish the ____________.

Lesson 19.4: Critical Writing

Name___________________ Class______________ Date________

Thoroughly answer the question below. Use appropriate academic vocabulary and clear and complete sentences.

Describe the amniotic egg and reptile reproduction.

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