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Section
2
2
The Skeletal
System
The Skeletal System
Objectives
Reading Preview
After this lesson, students will be able to
D.1.2.1 Identify the functions of the
skeleton.
D.1.2.2 Explain the role that joints play in
the body.
D.1.2.3 Describe the characteristics of bone
and how to keep bones strong and healthy.
Key Concepts
• What are the functions of the
skeleton?
• What role do joints play in the
body?
• What are the characteristics of
bone, and how can you keep
your bones strong and healthy?
Key Terms
Target Reading Skill
Asking Questions Explain that changing
a head into a question helps students
anticipate the ideas, facts, and events they are
going to read about.
Answers
Sample answers:
What does the skeleton do? (The skeleton
provides shape and support, helps you to move,
protects organs, produces blood cells, and stores
minerals and other materials.) How do joints
move? (Joints can move forward or backward,
in a circle, in a rotating motion, and in a
gliding motion.) How strong are bones?
(Bones can absorb more force without
breaking than granite or concrete.) What can I
do to care for my bones? (Eat a wellbalanced diet and get plenty of exercise.)
• skeleton • vertebra • joint
• ligament • cartilage
• compact bone • spongy bone
• marrow • osteoporosis
Target Reading Skill
Asking Questions Before you
read, preview the red headings. In
a graphic organizer like the one
below, ask a what or how question
for each heading. As you read,
answer your questions.
The Skeletal System
Question
Answer
What does the
skeleton do?
The skeletal
system provides
shape . . .
Teaching Resources
• Transparency D2
Think It Over
Observing Based on your observations, why do you think bones
are sometimes compared to rocks? List some ways in which
bones and rocks are similar and different.
A high rise construction site is a busy place. After workers have
prepared the building’s foundation, they begin to assemble
thousands of steel pieces into a frame for the building. People
watch as the steel pieces are joined to create a rigid frame that
climbs toward the sky. By the time the building is finished,
however, the building’s framework will no longer be visible.
Like a building, you also have an inner framework, but it
isn’t made up of steel. Your framework, or skeleton, is made up
of all the bones in your body. The number of bones in your
skeleton, or skeletal system, depends on your age. A newborn
has about 275 bones. An adult, however, has about 206 bones.
As a baby grows, some of the bones in the body fuse together.
For example, as you grew, some of the bones in your skull fused
together.
What the Skeletal System Does
Preteach
Build Background
Knowledge
Hard as a Rock?
1. Your teacher will give you a
rock and a leg bone from a
cooked turkey or chicken.
2. Use a hand lens to examine
both the rock and the bone.
3. Gently tap both the rock and
the bone on a hard surface.
4. Pick up each object to feel how heavy it is.
5. Wash your hands. Then make notes of your observations.
Just as a building could not stand without its frame, you would
collapse without your skeleton. Your skeleton has five major
functions. It provides shape and support, enables you to
move, protects your organs, produces blood cells, and stores
minerals and other materials until your body needs them.
L1
What Bones Look Like
Ask students to feel the bones beneath the
skin in one of their hands, then draw a
picture of what they think the bones look
like. Have students brainstorm what they
know or think they know about bones. List
these on a piece of poster paper, and address
misconceptions as you teach the section.
310 ◆
L1
Skills Focus Observing
Materials leg bone from a cooked
chicken or turkey, rock of similar size,
hand lens
Time 10 minutes
Tips Remind students to observe as many
characteristics as possible, such as size,
shape, color, texture, composition, and
310
strength. Make sure the chicken or turkey
bone has been thoroughly cooked and
washed.
Think It Over Possible answer: They are
both hard; bone is not as dense as rock and
has a definite structure. Bone is living,
while rock is not.
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Shape and Support Your skeleton determines the shape of
your body, much as a steel frame determines the shape of a
building. The backbone, or vertebral column, is the center of
the skeleton. Locate the backbone in Figure 6. Notice that the
bones in the skeleton are in some way connected to this column. If you move your fingers down the center of your back,
you can feel the 26 small bones, or vertebrae (VUR tuh bray)
(singular: vertebra), that make up your backbone. Bend forward at the waist and feel the bones adjust as you move. You
can think of each individual vertebra as a bead on a string. Just
as a beaded necklace is flexible and able to bend, so too is your
vertebral column. If your backbone were just one bone, you
would not be able to bend or twist.
Why is the vertebral column
considered the center of
the skeleton?
Instruct
What the Skeletal
System Does
Teach Key Concepts
Clavicle (collar bone)
Scapula (shoulder blade)
Phalanges
FIGURE 6
Metacarpals
The Skeleton
The skeleton provides a
framework that supports
and protects many other
body parts. Comparing and
Contrasting In what ways is
the skeleton like the steel
framework of a building? In
what ways is it different?
Humerus
Carpals
Radius
Sternum
(breastbone)
Ulna
Ribs
Vertebral column
(backbone)
Skull
Pelvic girdle
Femur
L2
Functions of the Skeleton
Focus Ask: What would your body be like
if you did not have a skeleton? (Sample
answers: You would not have a shape; you
would not be able to stand or perform any
other movements.)
Teach Ask students to identify as many
functions of the skeletal system as they can
by examining Figure 6. (Helps you to move,
provides shape, provides support, protects
organs) Ask: Why are vertebrae important?
(They are the bones that make up your
backbone, and all other bones are connected to
the backbone.) What other functions does
the skeletal system perform? (It produces
certain blood cells and stores minerals.)
Apply Explain that a bone’s structure relates
to its function. Ask students to locate these
bones in Figure 6 and identify their primary
function: Sternum (Protection), Carpals
(Movement), Femur (Support and
movement), Ribs (Protection), Vertebral
column (Protection, support, and movement)
learning modality: visual
Teaching Resources
Tibia
Patella
• Transparency D3
Fibula
Independent Practice
L2
Teaching Resources
• Guided Reading and Study Worksheet:
The Skeletal System
Tarsals
Metatarsals
Phalanges
Student Edition on Audio CD
Chapter 8
◆ 311
Monitor Progress
Differentiated Instruction
L1
English Learners/Beginning
Comprehension: Key Concept On the
board, rewrite the boldface sentence about
the five major functions of the skeleton
as individual sentences. Explain each
function. Then have students construct a
concept circle with “Functions of the
Skeletal System” in the center and the five
functions connected to the center by lines.
learning modality: visual
L2
English Learners/Intermediate
Vocabulary: Science Glossary Have
students write the definition of each Key
Term in this section in their own words,
and then write a sentence that uses each of
these words. learning modality: verbal
L2
Writing Ask students to list the five main
functions of the skeletal system.
Answers
Figure 6 Like the steel framework, the
skeleton shapes and supports the body.
Unlike the framework, the skeleton is living,
produces necessary materials, and is flexible.
The bones in the skeleton
are in some way connected
to the backbone.
311
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Joints of the Skeleton
Teach Key Concepts
Movement and Protection Your skeleton allows you to
move. Most of the body’s bones are associated with muscles.
The muscles pull on the bones to make the body move. Bones
also protect many of the organs in your body. For example,
your skull protects your brain, and your breastbone and ribs
form a protective cage around your heart and lungs.
L2
The Role of Joints
Focus Ask students to bend their right
elbows. Ask: What is the point where your
elbow bends? (Most students will know that
it is a joint.)
Teach Explain that joints hold bones
together. Not all joints are movable; two
bones can come together and not move—for
example, in the skull. Have volunteers read
aloud the captions in Figure 7. Ask a
question about each type of movable joint,
such as: What types of movements does the
ball-and-socket joint in the shoulder allow
the arm to make? (Up and down, backward
and forward, shrugging, in a circle) Then ask:
What do ligaments do? (They hold together
the bones in movable joints.) What substance
keeps bones from rubbing against each
other? (Cartilage)
Apply Instruct students to move one ear
back and forth, then the tip of their nose.
Explain that the flexible part is cartilage, the
same material that covers the ends of bones.
Extend The Active Art will show students
how joints move. learning modality: visual
For: Movable Joints activity
Visit: PHSchool.com
Web Code: cep-4012
Production and Storage of Substances Some of your
bones produce substances that your body needs. You can think
of the long bones of your arms and legs as factories that make
certain blood cells. Bones also store minerals such as calcium
and phosphorus. When the body needs these minerals, the
bones release small amounts of them into the blood.
Joints of the Skeleton
FIGURE 7
Movable Joints
Without movable joints, your body
would be as stiff as a board. The
different kinds of joints allow your
body to move in a variety of ways.
Comparing and Contrasting How
is the movement of a hinge joint
different from that of a ball-andsocket joint?
Suppose that a single long bone ran the length of your leg.
How would you get out of bed or run for the school bus? Luckily, your body contains many small bones rather than fewer
large ones. A joint is a place in the body where two bones come
together. Joints allow bones to move in different ways. There
are two kinds of joints—immovable joints and movable joints.
Hinge Joint
A hinge joint allows forward or
backward motion. Your knee is
a hinge joint that allows you to
bend and straighten your leg.
Your elbow is also a hinge joint.
Teaching Resources
• Transparency D4
Ball-and-Socket Joint
Ball-and-socket joints
allow the greatest range of
motion. The ball-and-socket
joint in your shoulder
allows you to swing your
arm freely in a circle.
Your hips also have
ball-and-socket joints.
Help Students Read
Comparing and Contrasting As students
read the section, have them create a table
that compares and contrasts the types
of joint.
312 ◆
312
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Immovable Joints Some joints in the body connect bones
in a way that allows little or no movement. These joints are
called immovable joints. The bones of the skull are held
together by immovable joints.
Movable Joints Most of the joints in the body are movable
joints. Movable joints allow the body to make a wide range of
movements. Look at Figure 7 to see the variety of movements
that these joints make possible.
The bones in movable joints are held together by strong
connective tissues called ligaments. Most joints have a second
type of connective tissue, called cartilage (KAHR tuh lij), which
is more flexible than bone. Cartilage covers the ends of the
bones and keeps them from rubbing against each other. For
example, in the knee, cartilage acts as a cushion that keeps your
femur (thighbone) from rubbing against the bones of your
lower leg. In addition, a fluid lubricates the ends of the bones,
allowing them to move smoothly over each other.
Classifying
Perform these activities.
•
•
•
•
•
•
Move your arm in a circle.
Push open a door.
Lift a book from a desk.
Kneel down.
Wave your hand.
Twist your head from side
to side.
Determine which type of
movable joint or joints is
involved in performing each
activity. Give a reason to
support your classifications.
How are movable joints held together?
Pivot Joint
A pivot joint allows
one bone to rotate
around another.
The pivot joint in
your neck allows
you to turn your
head from side to side.
For: Movable Joints activity
Visit: PHSchool.com
Web Code: cep-4012
Students explore the skeletal and
muscular systems.
L1
Observing Joints
Materials model of a human skeleton
Time 5 minutes whole class; 5 minutes per
pair or small group of students
Focus Show students the model and ask:
How does the human skeleton enable you
to move? (Bones are connected at joints and
can rotate, pivot, and bend back and forth.)
Teach Move one joint of each type on the
model, and state the type of joint as you
move it. Instruct students to take turns
examining the model in pairs, spending no
more than 5 minutes manipulating the
bones to see how the joints of the skeleton
move. Tell them to write down their
observations. You might schedule this
activity while students are working on their
Chapter Projects or doing independent
seat work.
Apply Make copies of a human skeleton,
and have students indicate each joint they
felt on the model and the name of the type
of joint. learning modality: kinesthetic
Gliding Joint
A gliding joint allows
one bone to slide over
another. The gliding
joint in your wrist or ankle
enables you to bend and
flex as well as make limited
side-to-side motions.
Monitor Progress
Chapter 8 ◆ 313
Skills Focus Classifying
Materials none
Time 15 minutes
Tips Students can work in pairs. One
student can perform the activity while the
other student observes the movement;
then partners can switch roles.
Expected Outcome Arm—ball and
socket joint (shoulder); door—hinge joint
(elbow), gliding joint (wrist); book—hinge
joint (elbow), gliding joint (wrist);
kneeling—hinge joint (knee); hand—gliding
joint (wrist); head—pivot joint (neck)
Extend Challenge students to
demonstrate the movement of other joints
and classify their types. learning
modality: kinesthetic
L2
Skills Check Ask students to identify the
different types of movable joints in addition
to the ball-and-socket joints in the picture
of the batter. (Neck—pivot joint; hands—
gliding; knees—hinge) Ask students to give an
example of a joint that is immovable. (Sample
answer: The bones of the skull)
Answers
Figure 7 A hinge joint allows only one type
of movement—forward or backward
motion. A ball-and-socket joint permits
movement in many directions.
By strong connective tissues
called ligaments
313
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Bones—Strong
and Living
Teach Key Concepts
FIGURE 8
L2
Characteristics of Bone
Focus Ask: Which function of the skeletal
system gives you a clue that bones are not
dead or solid? (Bones make certain blood cells
and release small amounts of minerals into the
blood when needed.)
Teach Refer students to Figure 8. Have them
locate and examine each part of the femur.
Ask: What covers the bone except for the
ends? (A thin, tough membrane) What is just
beneath this membrane? (Compact bone)
How do blood and other materials get to
the living cells inside the bone? (Blood
vessels run through canals in the compact
bone.) How does the structure of spongy
bone relate to its function? (Spongy bone has
many small spaces that make it lightweight but
strong.) Where is marrow produced? (In the
spaces in bone) What is marrow? (Two types
of soft, connective tissue; one type produces
some types of blood cells, the other type stores
fat.) Does new bone tissue stop forming
after you stop growing? (No; bones make
new tissue when they absorb the force of your
weight and when a bone has broken.)
Apply Have students write a paragraph
describing how the structure of bones allows
the bones to grow and makes them strong.
(Sample answer: The membrane allows blood
vessels to run through canals in the compact
bone to deliver materials the bone needs to
function. Spongy bone has spaces within it
that allow it to absorb large amounts of force.)
learning modality: visual
Teaching Resources
• Transparency D5
Femur
Bone Structure
The most obvious feature of a long bone,
such as the femur, is its long shaft. Running
through the compact bone tissue within the
shaft is a system of canals. The canals bring
materials to the living bone cells.
Interpreting Diagrams What different
tissues make up the femur?
Bones—Strong and Living
When you think of a skeleton, you may think of the paper cutouts that are used as decorations at Halloween. Many people
connect skeletons with death. The ancient Greeks did, too. The
word skeleton actually comes from a Greek word meaning “a
dried body.” The bones of your skeleton, however, are not dead
at all. Bones are complex living structures that undergo
growth and development.
Soft Bones?
In this activity, you will
explore the role that calcium
plays in bones.
1. Put on protective gloves.
Soak one clean chicken
bone in a jar filled with
water. Soak a second clean
chicken bone in a jar filled
with vinegar. (Vinegar
causes calcium to dissolve
out of bone.)
2. After one week, put on
protective gloves and
remove the bones from
the jars.
3. Compare how the two
bones look and feel. Note
any differences between
the two bones.
Drawing Conclusions Based
on your results, explain why
it is important to consume a
diet that is high in calcium.
Bone Structure Figure 8 shows the structure of the femur,
or thighbone. The femur, which is the body’s longest bone,
connects the pelvic bones to the lower leg bones. Notice that a
thin, tough membrane covers all of the bone except the ends.
Blood vessels and nerves enter and leave the bone through the
membrane. Beneath the bone’s outer membrane is a layer of
compact bone, which is hard and dense, but not solid. As you
can see in Figure 8, small canals run through the compact
bone. These canals carry blood vessels and nerves from the
bone’s surface to the living cells within the bone.
Just inside the femur’s compact bone is a layer of spongy
bone. Like a sponge, spongy bone has many small spaces
within it. This structure makes spongy bone tissue lightweight
but strong. Spongy bone is also found at the ends of the bone.
The spaces in many bones contain a soft, connective tissue
called marrow. There are two types of marrow—red and yellow. Red bone marrow produces most of the body’s blood cells.
As a child, most of your bones contained red bone marrow. As
a teenager, only the ends of your femurs, skull, hip bones, and
sternum (breastbone) contain red marrow. Your other bones
contain yellow marrow. This marrow stores fat that can serve
as an energy reserve.
What are the two types of bone marrow?
314 ◆
Skills Focus Drawing conclusions
Materials 2 plastic jars, vinegar, water,
2 clean chicken bones, gloves
Time 15 minutes for setup; 15 minutes
for observation
Tips
CAUTION: After students examine the
chicken bones, make sure they wash their
hands after removing the gloves.
314
Expected Outcome Bones soaked in
vinegar lose their calcium and become
rubbery; a diet high in calcium helps
keep bones hard.
Extend Ask students to examine food
labels at home to find food sources rich in
calcium, and then report their findings to
the class. learning modality: kinesthetic
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Canal
Compact Bone
L2
Observing Bone Structure
Materials leg bones from thoroughly cooked
chickens or turkeys, dissecting trays, gloves,
hand lens; before class, use a small kitchen
saw to slice one leg bone crosswise and one
lengthwise for each group. Place the bones
in the trays.
Time 15 minutes setup; 15 minutes class
Blood vessels
Compact
bone
Spongy bone
Focus Remind students that bones are
organs that are composed of different types
of tissue.
Teach
Have groups of students use Figure 8
to identify the various parts of the
bones. Ask them to write down and sketch
their observations. CAUTION: After students
examine the chicken bones, make sure they
wash their hands after removing the gloves.
Apply Ask: Where did you find the largest
concentration of compact bone and spongy
bone? (Compact in the shaft, spongy at the
ends) Explain that short bones, such as those
in the fingers, are mostly spongy bone. Ask
students to infer why long bones have more
compact bone. (Long bones, such as those in
the legs, must have harder, denser compact
bone to support the body.) learning
Bone
marrow
Outer
membrane
Bone Strength The structure of bone makes it both strong
and lightweight. In fact, bones are so strong that they can absorb
more force without breaking than can concrete or granite rock.
Yet, bones are much lighter than these materials. In fact, only
about 20 percent of an average adult’s body weight is bone.
Have you ever heard the phrase “as hard as a rock”? Most
rock is hard because it is made up of minerals that are packed
tightly together. In a similar way, bones are hard because they
contain minerals—primarily phosphorus and calcium.
Bone Growth Bones are alive—they contain cells and tissues, such as blood and nerves. Because they are alive, bones
also form new bone tissue as you grow. Even after you are
grown, however, bone tissue continues to form within your
bones. For example, every time you play soccer or basketball,
some of your bones absorb the force of your weight. They
respond by making new bone tissue.
Sometimes, new bone tissue forms after an accident. If you
break a bone, for example, new bone tissue forms to fill the gap
between the broken ends of the bone. In fact, the healed region
of new bone may be stronger than the original bone!
modality: visual
FIGURE 9
Bone Strength
You can jump up and down or
turn cartwheels without
breaking bones.
Monitor Progress
Chapter 8 ◆ 315
Differentiated Instruction
L3
Gifted and Talented
Investigating the Effects of
Microgravity Tell students that weightbearing exercise promotes bone growth
and prevents bone loss. Exercises
performed against the force of gravity
stimulate osteoblasts, the cells that make
bone. Ask students to find out the effects of
microgravity on the bones of astronauts
and how scientists are using this
information to help people with spinal
cord injuries and people with osteoporosis.
(Students may discover some interesting
facts, for example, that some astronauts on
the space station Mir lost 13% of their bone
mass, mostly from the legs.) Ask students to
present a report to the class. learning
modality: verbal
L2
Skills Check Have students draw concept
maps showing the structure of bone. Suggest
that students draw concentric circles
indicating the layers of tissue and draw
arrows where blood vessels and
nerves flow through. Students can
save their concept maps in their
portfolios.
Answers
Figure 8 Compact bone, bone marrow,
spongy bone, outer membrane
Red blood marrow produces
some of the body’s blood
cells. Yellow marrow stores fat that can serve
as an energy reserve.
315
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Address Misconceptions
L1
Bones Are Living
Focus Some students might think that bone
is dead.
Teach Explain that some people think of
bones as lifeless because they see skeletons in
movies or skeletons of dead animals. Bone
does contain nonliving material, such as
calcium. However, it is composed of living
tissue. Ask: What are the levels of
organization before bones? (Cells, then
tissues) What kinds of functions do these
perform? (Cells grow, reproduce, and take in
energy. Tissues perform a specific function.)
Point out that bones are living because they
are made of cells and tissues, which compose
all living things.
Apply Ask: Would a bone bleed if it were
cut? (Yes, because bones have blood vessels)
Would it hurt? (Yes, because bones have
nerves) learning modality: verbal
Bones, Muscle,
and Skin
Video Preview
Video Field Trip
Video Assessment
Bone Development Try this activity: Move the tip of your
nose from side to side with your fingers. Notice that the tip of
your nose is not stiff. That is because it contains cartilage. As
an infant, much of your skeleton was cartilage. Over time,
most of the cartilage was replaced with hard bone tissue.
The replacement of cartilage by bone tissue usually is complete by the time you stop growing. You’ve seen, however, that
not all of your body’s cartilage is replaced by bone. Even in
adults, many joints contain cartilage that protects the ends of
the bones.
Taking Care of Your Bones
Because your skeleton performs so many necessary functions,
it is important to keep it healthy. A combination of a balanced
diet and regular exercise are important for a lifetime of
healthy bones.
Diet One way to help ensure healthy bones is to eat a well-
balanced diet. A well-balanced diet includes enough calcium
and phosphorus to keep your bones strong while they are
growing. Meats, whole grains, and leafy green vegetables are all
good sources of both calcium and phosphorus. Dairy products,
including yogurt, are good sources of calcium.
Exercise Another way to build and maintain strong bones is to
get plenty of exercise. During activities such as running, skating,
or dancing, your bones support the weight of your entire body.
These weight-bearing activities help your bones grow stronger
and denser. To prevent injuries while exercising, be sure to wear
appropriate safety equipment, such as a helmet and pads.
Taking Care of
Your Bones
Teach Key Concepts
L2
Habits for Strong, Healthy Bones
Focus Remind students that calcium is a
mineral that helps bones to be hard.
Teach Ask: How can you get enough
calcium? (Eat a well-balanced diet that
includes good sources of calcium.) What kind
of exercise helps your bones grow stronger
and denser? (Activities in which your bones
support the weight of your body) How can
you reduce your risk of osteoporosis? (Eat
calcium-rich foods and get plenty of exercise)
Tell students that osteoporosis can be largely
prevented by building bone mass during
adolescence and young adulthood.
Apply Encourage students to create a list of
activities that are weight-bearing and a list of
those that are not. (Weight-bearing activities
include jogging, aerobics, walking, jumping
rope, weight lifting, skating, dancing, soccer,
and basketball. Non-weight-bearing activities
include cycling and swimming.) learning
modality: verbal
316
What are two ways to keep your bones healthy?
FIGURE 10
Caring for Your Bones
Exercising regularly and
eating a balanced diet help
to keep your bones strong
and healthy.
316 ◆
Show the Video Field Trip to let students
experience a trip through a bone and
understand the structure and function of
bones. Discussion question: What happens
to the cartilage that makes up much of an
infant’s skeleton? (It is replaced by bone
tissue as the child grows.)
sx05_TE_(nc7-8)c01D.fm Page 317 Tuesday, June 7, 2005 4:39 PM
Healthy Spine
Monitor Progress
Spine with Osteoporosis
FIGURE 11
Osteoporosis
Without enough calcium in the diet,
a person’s bones weaken. These
photos show how the shape and
structure of vertebrae in a healthy
spine compare with those in a
person with osteoporosis.
Relating Cause and Effect What can
you do to prevent osteoporosis?
L2
Answers
Figure 11 Exercise regularly and eat a diet
with enough calcium.
Eat a well-balanced diet
and get plenty of exercise.
Assess
Reviewing Key Concepts
1. a. Provide shape and support, enable you
Osteoporosis As people become older, their bones begin
to lose some of the minerals they contain. Mineral loss can lead
to osteoporosis (ahs tee oh puh ROH sis), a condition in which
the body’s bones become weak and break easily. You can see the
effect of osteoporosis in Figure 11. Osteoporosis is more common in women than in men. Evidence indicates that regular
exercise throughout life can help prevent osteoporosis. A diet
with enough calcium can also help prevent osteoporosis. If you
eat enough calcium-rich foods now, during your teenage years,
you may help prevent osteoporosis later in life.
2
Section 2 Assessment
Target Reading Skill Asking Questions Work with a
partner to check the answers in your graphic organizer.
Reviewing Key Concepts
1. a. Listing What are five functions of the skeleton?
b. Explaining How does the skeleton protect the body?
c. Predicting How would your life be different if your
backbone consisted of just one long bone?
2. a. Naming What are four types of movable joints?
b. Comparing and Contrasting Compare immovable
joints with movable joints.
c. Classifying Which of your movable joints are ball-andsocket joints?
3. a. Describing Describe the structure of the femur.
b. Relating Cause and Effect How does the structure of
bones make them both strong and lightweight?
c. Applying Concepts How do a well-balanced diet and
weight-bearing exercise help keep bones strong?
Model Joints Choose two examples
of movable joints from Figure 7.
Ask a family member to perform
separate movements that involve
one joint and then the other. Make
drawings to represent the joints
and bones involved in each
movement. Use the drawings to
explain to your family how the
motions of the two joints differ.
to move, protect your organs, produce blood
cells, and store minerals and other materials
b. The skull protects the brain, and the
breastbone and ribs protect the heart and
lungs. c. Sample answer: You could not bend
at the waist or twist. You would not be able to
do some activities you do now, such as certain
sports, twisting to get something behind you,
or getting out of bed the same way.
2. a. Hinge, ball-and-socket, pivot, and
gliding b. Both immovable and movable
joints join two bones. Immovable joints
allow little or no movement. Movable joints
allow the body to make a wide range of
movements. c. Shoulders and hips
3. a. Compact bone, spongy bone, and
marrow b. Compact bone is hard and
dense. Spongy bone has many small spaces
within it that make it strong but lightweight.
c. A well-balanced diet contains calcium and
phosphorus, which bones need to keep them
strong. Weight-bearing exercises help bones
grow stronger and denser.
Reteach
L1
Call on students to define the Key Terms in
this section and relate each to the Key
Concepts.
Performance Assessment
Chapter 8 ◆ 317
L2
Writing Ask students to describe one of the
major functions of the human skeleton and
explain how the skeleton carries out that
function.
Teaching Resources
Keep Students on Track Check that
students have completed their designs and
sketches of the model hands, and have
begun building their models. Approve all
designs, and help students locate
materials. Remind students that they can
use parts from other devices, such as
discarded or broken toys.
Model Joints L2 As a class, review
the different types of joints and their
movements. Suggest that students
closely note the direction of the
movement when a family member
performs it. Advise them to keep their
drawings simple to emphasize the
movement.
• Section Summary: The Skeletal System
• Review and Reinforce: The Skeletal System
• Enrich: The Skeletal System
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