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Lesson 6What Animal Structures Are Used for Support, Movement, and Protection?

© Teachers’ Curriculum Institute100 Lesson 6 What Animal Structures Are Used for Support, Movement, and Protection?

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Think of what you already know about the ways in which different animals move. Write questions you have.

Discuss: Have you ever seen a snake move around? What shapes did the snake’s body make?

Observe this phenomenon: Snakes move without legs.

Take a trip to a local ecosystem. Investigate how different animals in this ecosystem move.

See It!

101© Teachers’ Curriculum Institute Lesson 6 What Animal Structures Are Used for Support, Movement, and Protection?

I N V E S T I G A T I O N

Observing Phenomena

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Observing Pill BugsInvestigation Question: What structures do pill bugs have for movement and protection?• Gather the materials needed to observe live pill bugs.• Observe your pill bugs. Find evidence to answer the investigation

question.• Answer the questions about movement and protection with a claim

and supporting evidence.• Share your findings with the class.

What structures do pill bugs have that help them move around?

Claim (write an answer to the question):

Evidence (draw and label a diagram of what you observed):

102 © Teachers’ Curriculum InstituteLesson 6 What Animal Structures Are Used for Support, Movement, and Protection?


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What structures (or behaviors) do pill bugs have to protect themselves?

Claim (write an answer to the question):

Evidence (draw and label a diagram of what you observed):



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Are pill bugs supported by an internal skeleton or an exoskeleton? List two ways that you could investigate this question.

Now, clean up. Carefully return the pill bugs to their habitat.



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Vocabulary

My Science Concepts

Match the word to its definition.

Word Bank

joint skeleton muscle exoskeleton

1. A hard covering on the outside of an insect’s body.

2. A structure made up of all the bones in an animal’s body.

3. A structure that contracts and relaxes to produce movement.

4. A place where two or more bones come together.

Reflect on your understanding. Draw an X along each line.

Some animals have an internal skeleton that supports their bodies. These animals move by flexing muscles attached to their bones. Other animals might have exoskeletons. They move by muscles attached to their legs or wings that connect to their exoskeletons.

still learning know it

Most animals move to get away from danger. Others produce poisonous substances or grow sharp quills for protection. Pill bugs use the plates along their exoskeleton to help protect them. They roll into a ball to cover their soft body parts and have seven pairs of legs to help them move.


Scientists observe and study animal behavior. This helps them make arguments about the function of different structures.




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1. Bones Make up the Skeleton

If you put your hand on your chest, you can feel hard structures underneath your skin. Those are your ribs, a set of bones inside your body. Why do you and many other animals need bones?

A bone is a hard structure inside some animals’ bodies. Bones and other structures that provide support to the body make up the skeleton. A skeleton also contains cartilage, a strong and flexible material. Together, bones and cartilage support an animal’s body. The skeleton also helps protect soft parts inside the body. For example, your ribcage protects your heart and lungs.

Many bones make up the skeleton. A backbone is a row of small bones that runs along the inside of these animals’ backs. Arms and legs contain long bones. A skull protects the brain inside the animal’s head. Smaller bones make up the ribs of the chest. Bones grow and change like other parts of the body. The skeleton also helps these animals move.

Two or more bones come together at a joint. Several kinds of joints allow different kinds of movement. For example, the elbow and knee are hinge joints. The bones in a hinge joint move back and forth like a door hinge. Ball and socket joints in the shoulders and hips let the bones move in a circle.

This is an X-ray of a dog’s foot. Dogs have many different bones in their bodies, and those bones support their body weight.

This is what the skeleton inside your body looks like. Each bone is connected to other bones at joints.

Hinge joint

Ball and socket joint


T E X T W I T H N O T E S

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You have already learned that your elbows and knees are hinge joints. Look at this picture of a deer running again. Where do you think it might have hinge joints in its skeleton? What about ball and socket joints? Why do you think that?



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2. Muscles Move Bones

The bones in your arm move to straighten or bend your arm. But bones cannot move by themselves. What structures in animals helps them move?

A muscle is a structure that contracts and relaxes to produce movement. When a muscle contracts, it gets shorter. When it relaxes, it gets longer. When a muscle pulls on a bone, it moves. Muscles often work in pairs. When one muscle in a pair contracts and gets shorter, the other muscle in the pair relaxes and gets longer. Muscles work closely with bones to allow animals to move. For example, an animal with legs can walk by contracting and relaxing the muscles attached to its leg bones.

You may have watched a snake move. Snakes have no legs, but they move by contracting the muscles on the right side and the left side of their body back and forth. The snake’s body first is pulled to the right and then to the left in an S-shaped motion. Each contraction moves the snake forward.

Some muscles in the body are not attached to bones. For example, recall that the heart is made of muscles. When the heart muscles contract, blood is pumped through the body. The muscles in the stomach and throat contract and relax to push food through the body.

Muscles often work in pairs. When one muscle contracts, the other usually relaxes.

A snake’s bones and muscles work together to cause movement. Snakes move in an S-shaped pattern.

Muscles in the Human Arm

Relaxed muscle

Bones

Relaxed muscle

Contracted muscle

Bones

Contracted muscle



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Describe how a snake moves. Use these terms: muscle, contract, relax, and s-shape.



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3. Bird and Fish Structures for Movement

Birds and fish have muscles, like other animals. But what unique structures do they use to move?

Most birds have unique structures that help them fly. A bird has a skeleton, like you, but its bones are very different. Bones inside a bird’s wings are hollow. Hollow bones are very strong and more flexible. Having flexible bones helps keep a bird in the air.

Most birds are also covered in feathers. A feather is a lightweight, flat structure that forms the outside covering of a bird’s body. Even though they feel soft, feathers are made of the same strong material as your fingernails. They make a bird’s body smooth, so it can glide through the air easily. Long tail-feathers help a bird balance and steer.

Fish also have unique structures, but not to fly. Fish have fins and a tail to move through the water. A fin is a flattened structure on the outside of a fish. Fins help the fish move, steer, and balance, and the tail fin pushes water to propel the fish forward.

Like birds, fish must also have a smooth body. Most fish are covered with hard, slippery scales. A scale is a stiff flattened plate. Many scales together form a protective covering on the outside of a fish. But not all fish have scales. For example, catfish have no scales.

This is a bird’s skeleton. Most birds have very flexible, strong, and hollow bones, so they can fly.



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This is a picture of a whale shark. Describe how it moves. Make sure you include the following structures in your answer: fin, tail fin, and scales.



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4. Animals Without Backbones Need Support

All the animals you have read about have bony skeletons inside their bodies. But many kinds of animals have no bones. How can an animal support its body without bones?

Land animals without bones cannot grow very large. Many of these boneless animals are insects. Insects have a kind of skeleton, but it is not made of bone, and it is not inside the insect’s body. An insect’s skeleton, called an exoskeleton, is a hard cover and is on the outside of its body. The cover protects the insect’s soft body parts and gives it support. Unlike bones, an exoskeleton cannot grow. When an insect gets too big, a new, larger cover forms under the old one. Then the insect sheds the old cover. The new cover is soft at first, but it quickly hardens.

Many animals with no bones live in water, like squid. The water pushes against the animal’s body and supports its weight. Other animals have a water-filled structure inside their bodies. The water pushes outward and supports the animal from the inside.

Have you ever seen shells on a beach? The shells are the remains of clams and oysters. Hard shells protect and support their soft bodies and make it harder for other animals to eat them.

This is an insect’s exoskeleton. It is the hard outer covering that protects and supports the insect.

This is a giant clam. Its body is very soft, with no bones. But it is protected and supported by hard, outer shells.



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Look at each group of animals. What is one structure that they all have in common? What does that structure do? Make sure you use these terms in your answer: shell, water-filled, and exoskeleton.



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5. Other Structures Allow Movement

Most animals without bones can still move. They just do not move the way you do.

Insects have six jointed legs, which allow the insect to walk and jump. An insect’s muscles are inside its body, and are attached to its exoskeleton. Many insects also have wings and can fly. Muscles move the wings up and down over and over very quickly.

The body of an earthworm contains water-filled structures and muscles throughout the worm’s body. When the worm’s muscles contract, they pull against the water-filled structures. That part of the worm moves forward. An earthworm also has stiff hairs on the bottom of its body. The hairs attach to a surface so the worm does not slide backwards when it moves forward.

Snails move with a single foot. The foot is a muscle that contracts and relaxes to move the snail forward. A snail also has a structure that produces slime. The slime helps the snail glide along the ground.

Squids and octopuses move in two ways. They crawl along the ocean floor, using the suckers on their eight arms to grab rocks. When a squid needs to move quickly, it pulls water into a structure in its body and then pushes the water out through a tube. The force of the squirting water pushes the squid backward through the water.

This is a snail. Most of its body that you can see in this picture is a muscle, called a foot. It moves by contracting and relaxing its foot.

This earthworm uses muscles and water-filled structures to move. The water-filled structures work like a skeleton, and the muscles can contract and relax against them to move the worm forward.



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Look at this picture of a snail and describe what structures it is using to move. Use these terms: foot, muscle, contract, relax, and slime.



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6. Animal Structures for Protection

You learned that plants protect themselves with things such as thorns, chemicals, and waxy leaves. But how do you think animals protect themselves?

Many animals protect themselves by moving. If a snake is trying to eat a mouse, that mouse will run away as fast as it can. The mouse’s muscles and bones move in ways that protect it from animals like snakes.

Like some plants, other animals protect themselves with chemicals. Some insect caterpillars have structures that produce poisonous or bad-tasting substances. If a bird tries to eat a poisonous caterpillar, it will get sick. That bird will learn not to eat that species of caterpillar.

Some animals have structures that let them hide. For example, a pygmy seahorse has skin that is bumpy, pink, and white. It looks very similar to coral where it lives, so if the seahorse stays still, other fish cannot see it.

Other animals, such as porcupines, have sharp structures on the outside of their bodies for protection, called quills. A quill is a type of hair that is hard and sharp. Porcupines are hard to eat because these quills can be very dangerous.

There is a pygmy seahorse in this picture. It has pink and white skin, covered with bumps, so it looks very similar to the coral around it. Can you find the seahorse?

This is a porcupine. Those white and black hairs growing out of its body are sharp quills. If a fox or a wolf tries to eat it, the porcupine will turn its quills toward the attacker to defend itself.



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Design your own animal that has some structures for protection. Maybe it has long legs, sharp quills, or can make poisonous substances. Draw your new animal below, and label at least one structure that it uses for defense.



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Show What You Know

Think of an animal that has not been discussed in this lesson. Find or draw a picture of it below.

Make an argument for how this animal supports itself, moves, and protects itself. As evidence, use what you learned in the text and during the investigation.


C H E C K F O R U N D E R S T A N D I N G

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Making Sense of the Phenomenon

Claim

Evidence

Reasoning

Use your findings from the investigation to answer this question:

Do you think snakes are supported by an internal skeleton or an exoskeleton?

Go back to page 4 and fill out the unit checkpoint for this lesson.

Let’s revisit the phenomenon: Snakes move

without legs.

Think about:• What structures is the snake using for support,

movement, and protection?• How do these structures help the snake survive?


C H E C K F O R U N D E R S T A N D I N G

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