Here are the results of the experiment: 1. The chicken bone in the empty jar could not be bent. 2. The chicken bone in water could still not be bent. 3. The chicken bone in vinegar could easily be bent. The vinegar dissolved the minerals like calcium from the chicken bone, making it soft and easy to bend. This shows that without minerals like calcium, bones lose their hardness and strength. The experiment demonstrates what happens when bones lose their mineral content - they become soft and can be easily bent or broken. The vinegar mimics the process of demineralization by dissolving the calcium from the bone.

1. Smart Science 4
Textbook

2. Smart Science
GRADE 4
TEXTBOOK
Philippine Copyright 2009 by DIWA LEARNING SYSTEMS INC
All rights reserved. Printed in the Philippines
Editorial, design, and layout by University Press of First Asia
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ISBN 978-971-46-0091-1
REVIEWER
Marina E. Balce was a former assistant dean and associate professor at the College of Education,
La Salle College–Antipolo. She taught biological sciences for Psychology students and thesis writing
for graduating Education students in the same college. She was also a Trainee of the Japan International
Cooperation Agency (JICA) at the Aichi University in Nagoya, Japan, where she attended a special
training on Practical Work in Elementary School Science. Dr. Balce finished her bachelor’s degree in
Secondary Education major in Biology at the University of the East–Manila. She has a master’s degree
in Biology Education from the De La Salle University–Manila and a doctorate in Science Education
major in Biology from the University of the Philippines–Diliman.

3. To the Learner
Do you ask yourself questions about the world you live in? Do you
wonder about what lies beyond the blue skies or what rests below the
seas? Do you ask questions about the blooming trees and colorful flowers
you see, the heat and cold you feel, or the various scents you smell? Do
you wonder about the sun, the moon, and the stars? Your young, active
mind has so many questions because you are curious about so many
things.
This book will help you discover the answers to the questions you
have about yourself, the world, and everything beyond it. This book will
be your constant companion as you unlock the many mysteries of life
through various learning experiences. Moreover, this book will teach you
how to apply the wonders of science to your day-to-day activities.
Let this book help you find the answers to the questions you have
about yourself, your world, and the universe. Let this take you a step closer
to understanding life and in discovering the wonders of science!

4. Unit 1 Human Body Systems: Skeletal, Muscular, and
Digestive
Chapter 1 The Skeletal System
Lesson 1 The Parts of the Skeletal System ......................................................... 2
Lesson 2 Disorders and Diseases of the Skeletal System ................................. 13
Lesson 3 Caring for Your Bones ..................................................................... 19
Think Back ....................................................................................................... 23
Measure Up! ....................................................................................................... 24
Chapter 2 The Muscular System
Lesson 1 The Muscles and Their Functions .................................................... 27
Lesson 2 Types of Muscles ............................................................................. 34
Lesson 3 Disorders and Diseases of the Muscular System ............................... 37
Lesson 4 Caring for Your Muscles .................................................................. 41
Think Back ....................................................................................................... 45
Measure Up! ....................................................................................................... 46
Chapter 3 The Digestive System
Lesson 1 Inside the Digestive System ............................................................. 49
Lesson 2 Taking in Food through the Mouth .................................................. 54
Lesson 3 Down the Esophagus ....................................................................... 57
Lesson 4 Digestion in the Stomach ................................................................ 59
Lesson 5 Digestion in the Small Intestine ....................................................... 63
Lesson 6 Digestion in the Large Intestine ....................................................... 66
Lesson 7 Diseases and Disorders of the Digestive System .............................. 70
Lesson 8 Caring for Your Digestive System .................................................... 76
Think Back ....................................................................................................... 79
Measure Up! ....................................................................................................... 80
Unit 2 The World of Animals and Plants
Chapter 4 The World of Animals
Lesson 1 Animal Reproduction ...................................................................... 86
Lesson 2 Baby Animals .................................................................................. 91
Lesson 3 Life Cycles ....................................................................................... 95
Lesson 4 Complete Metamorphosis ................................................................ 99

5. Lesson 5 Incomplete Metamorphosis ........................................................... 103
Lesson 6 Beneficial and Harmful Animals .................................................... 106
Lesson 7 Protection from Harmful Animals .................................................. 112
Lesson 8 Endangered Animals ...................................................................... 116
Think Back ..................................................................................................... 119
Measure Up! ..................................................................................................... 120
Chapter 5 The World of Plants
Lesson 1 The Flower and Its Parts ................................................................ 122
Lesson 2 How Do Plants Reproduce? ........................................................... 129
Lesson 3 Fertilization in Flowers .................................................................. 132
Lesson 4 Seed: Parts and Functions .............................................................. 135
Lesson 5 Seed Germination ......................................................................... 138
Lesson 6 Spreading Seeds ............................................................................ 141
Lesson 7 Plants Also Reproduce Asexually ................................................... 144
Lesson 8 Conserving Plants .......................................................................... 149
Think Back ..................................................................................................... 152
Measure Up! ..................................................................................................... 153
Unit 3 Matter, Energy, and Force
Chapter 6 Matter All around Us
Lesson 1 What Is Matter? ............................................................................. 156
Lesson 2 Properties of Matter ....................................................................... 160
Lesson 3 What Are Mixtures? ....................................................................... 166
Think Back ..................................................................................................... 169
Measure Up! ..................................................................................................... 170
Chapter 7 Energy and Force
Lesson 1 Heat It Up! .................................................................................... 172
Lesson 2 How Heat Is Transferred ................................................................ 177
Lesson 3 Safety First ..................................................................................... 183
Lesson 4 Friction .......................................................................................... 187
Lesson 5 Controlling Friction ....................................................................... 190
Think Back ..................................................................................................... 194
Measure Up! ..................................................................................................... 194

6. Unit 4 The Changing Earth, Weather, and Beyond
Chapter 8 The Changing Earth
Lesson 1 Water as an Agent of Change ........................................................ 198
Lesson 2 Temperature and Rocks ................................................................. 202
Lesson 3 Wind and Soil Erosion ................................................................... 204
Lesson 4 Plants and Animals Break Rocks .................................................... 208
Lesson 5 People Can Also Break Rocks ........................................................ 211
Lesson 6 Ways to Prevent Soil Erosion ......................................................... 214
Think Back ..................................................................................................... 218
Measure Up! ..................................................................................................... 219
Chapter 9 Weather Elements
Lesson 1 Different Weather Elements ........................................................... 221
Lesson 2 Observing Changes in Air Temperature ......................................... 224
Lesson 3 Observing Changes in Wind Speed and Direction ......................... 228
Lesson 4 Observing Cloud Formations ......................................................... 233
Think Back ..................................................................................................... 237
Measure Up! ..................................................................................................... 238
Chapter 10 The Sun-Moon-Earth System
Lesson 1 The Moving Earth .......................................................................... 240
Lesson 2 Earth Revolves around the Sun ...................................................... 243
Lesson 3 The Moon in Motion ..................................................................... 246
Lesson 4 Moon Phases ................................................................................. 249
Lesson 5 Eclipses ......................................................................................... 252
Lesson 6 Tides ............................................................................................. 257
Think Back ..................................................................................................... 261
Measure Up! ..................................................................................................... 262
Bibliography ............................................................................................................. 265

7. Unit 1 Human Body Systems:
Skeletal, Muscular,
and Digestive
Your body is composed of parts that work together to keep you alive.
These parts perform their specific functions so efficiently that you hardly
notice them working at all!
Activities that are as simple as the movement of your finger or as
complex as the digestion of the food that you have eaten are results of the
important functions of your body systems.
In this unit, learn about three body systems, namely, skeletal,
muscular, and digestive. Know which diseases can affect them and how to
take good care of them.

8. Chapter 1
The Skeletal System
Have you seen a building undergoing construction? What have you
observed?
As you may have noticed, constructing a building starts by putting
together a system of beams and girders, or what is called a framework. The
framework is held together by special bolts to make it strong. It must be
strong because it provides support to the floors and walls of the building.
This way, the building does not collapse.
The human body is just like a building. It has a framework called
the skeleton which is made up of superbly joined and balanced system of
bones held by ligaments, tendons, and joints.
Lesson 1
The Parts of the Skeletal System
Find Out
1. What are the functions of the skeletal system?
2. What are the parts of the skeletal system? What are the functions of
each part?
3. How are the bones in the human body classified?
4. What are cartilage, joint, and ligament?
Your skeleton gives your body support, shape, and protection. It is made
up of bones that have different shapes, sizes, and functions.
2 Smart Science 4

9. The Bones
As a newborn, you may have as many as 350 bones. Soon after birth,
your bones start to harden and some of them fuse together. This is due
to the accumulation of materials such as calcium and phosphorus in the
bones. This process is called ossification. As bones fuse together, they form
fewer but bigger and stronger bones. The hardening of the bones continues
until early adulthood. An adult’s skeletal system consists of 206 bones.
skull
clavicle
sternum
ribs humerus
vertebral column
radius
ulna pelvic girdle
bones of the hand
femur
patella
tibia
fibula
bones of the foot
An adult’s skeletal system
The bones of the body are grouped into two: the axial and
perpendicular skeletons.
The axial skeleton consists of the skull, the backbone, and the rib cage.
The axial skeleton is made up of 80 bones.
Human Body Systems: Skeletal, Muscular, and Digestive 3

10. The skull protects the brain. It consists of 22 different bones—eight
paired bones and six unpaired bones. The bones of the skull are divided
into the cranial bones and the facial bones. The cranial bones hold and
protect the brain. The facial bones, which are found below the skull,
provide the framework that forms the face.
Facial Bones Cranial Bones
ethmoid bone frontal bone
lacrimal bone parietal bone
nasal bone sphenoid bone
zygomatic bone temporal bone
maxilla lacrimal bone
mandible occipital bone
Bones of the skull
Get a partner and run your fingers down the middle of his
or her back. Describe the body part that you feel.
The backbone is a chain of bones that runs down the
middle of your back. It is also called the spine or vertebral
column. There are 26 vertebrae (or bones of the spine)
attached together by joints. The backbone protects the thick
cord of nerves called the spinal cord.
The backbone
4 Smart Science 4

11. The bones at the sides of your chest form the rib
cage. The rib cage protects the heart, lungs, and other
internal organs. It also helps you breathe. It consists
of 12 pairs of flat, curved bones called ribs. They are
connected to each other by muscles. The first upper ribs,
called the true ribs, curve around from the spine and join
the breast bone in front. The next three pairs are called
the false ribs. Each false rib is connected to the rib above
it. The lowest two pairs of ribs, called the floating ribs,
are attached only to the backbone.
sternum
true ribs
false ribs
floating ribs
The rib cage
Place your hand against your chest. The flat bone that you can feel in
front of your chest is the sternum or breast bone. It is connected to the ribs
by cartilage.
Breathe deeply three times. Does your chest expand each time you
inhale? The cartilage that connects the sternum to the ribs can stretch,
allowing you to breathe deeply.
Human Body Systems: Skeletal, Muscular, and Digestive 5

12. The appendicular skeleton is made up of the bones of the girdles and
appendages. The appendages include the arms, hands, legs, and feet. There
are two girdles in the human body—the pectoral girdle and pelvic girdle.
The appendicular skeleton is made up of 126 bones.
Pectoral girdle Pelvic girdle
The pectoral girdle allows you to move your arms and anchors them
in your skeleton. The pelvic girdle connects your lower extremities to the
axial skeleton and supports your abdominal organs.
Your hands are the most
nimble parts of your body.
You use them to hold
heavy objects, but they
are also suited to perform
delicate tasks like threading
a needle.
The bones of your
feet bear the entire weight
of your body. When you
stand, walk, or jump, your
feet give you support and
balance.
6 Smart Science 4

13. Have you wondered how your bones are distributed in your body? The
table below shows the distribution of bones in the human body.
The Bones of the Body
Types of Skeleton Number of Bones
Axial Skeleton 80 bones
backbone 26
ribs 24 (12 on each side)
skull 22
ears 6 (3 each)
throat 1
sternum 1
Appendicular Skeleton 126 bones
hands 56 (28 each)
feet 52 (26 each)
legs 6 (3 each)
arms 6 (3 each)
shoulders 4
hips 2
Total 206 bones
The Parts of the Bone
The outer layer of
the bone is called the compact bone spongy
compact bone. This bone
layer is dense and
looks smooth. It forms spongy bone
(spaces contain
the protective outer red bone marrow)
part of all bones. The compact bone
compact bone helps yellow bone
withstand bumps and blood vessel
central cavity blood vessels and
bangs that your bones (contains yellow nerve in central canal
may encounter. It also bone marrow)
consists of minerals The bone structure
such as phosphorus and
calcium.
Human Body Systems: Skeletal, Muscular, and Digestive 7

14. Inside the compact bone is the spongy bone, which is very porous.
The spaces in the spongy bone are filled with blood and soft tissue, called
red marrow. The red marrow produces red blood cells, some white blood
cells, and platelets. It also repairs the compact bone.
Calcium and phosphorus are the minerals needed to build strong
bones. What do you think will happen if bones do not have these
minerals? The experiment below will help you find out what happens
when bones lose their mineral content.
Explore
Removing Minerals from the Bones
You need:
three chicken bones (same part/size), three small jars, vinegar, water,
gloves
Do the following:
1. Clean the chicken bones thoroughly. Try to bend each bone carefully.
Can you bend them? __________________________________________
2. Half-fill one jar with water and the other with vinegar. Leave the third
one empty.
3. Put one chicken bone into each jar. Label the setups as follows: “Bone
in Water,” “Bone in Vinegar,” and “Bone in Jar.”
4. Leave the jars in a safe place for two days.
5. After two days, remove the chicken bones from the jars and carefully
wash them with water. Air dry the bones and then try to bend them.
Compare the texture of the three bones.
a. Which bone(s) can be bent? ________________________________
b. Which bone(s) cannot be bent? _____________________________
c. What did the vinegar do to the chicken bone? _________________
8 Smart Science 4

15. If calcium and phosphorus are removed, bones lose their hardness
and strength. This is why it is important for you to eat food rich in these
minerals to keep your bones strong and healthy. Dairy products such as
milk and cheese are rich in calcium. Vitamin D also keeps your bones
strong because it helps your body absorb calcium.
Cartilage, Joints, and Ligaments
When you were born, most of your bones were not yet fully developed.
They were made up mostly of cartilage. Cartilage is a tough, semi
transparent, elastic tissue. Almost all bones develop from cartilages. Cartilage
has several functions. It covers the surface of joints, allowing bones to slide
over one another, reducing friction and preventing damage. The cartilage
also acts as a shock absorber.
bone
cartilage
bone
Cross-section of a joint
Feel your elbow and your knee. You can flex and extend your arm
because of your elbow. You can perform the same movements with your
legs. This is all because of your joints. A joint is a point where two bones
meet. Joints allow your body to move in many ways.
Joints are classified by their range of movement. Immovable joints, called
fibrous joints, do not move. The dome of the skull, for example, is made of
bony plates, which must be immovable to protect the brain. Between the
edges of these plates are links or joints of fibrous tissue. Fibrous joints also
hold the teeth in the jawbone.
Human Body Systems: Skeletal, Muscular, and Digestive 9

16. nasal bone Partially movable joints or
cartilaginous joints move a little.
cartilage They are linked by a cartilage.
Examples of cartilaginous joints are
those in the windpipe or trachea,
bridge of the nose, and ears.
Freely movable joints or synovial
Bone cartilage of the nose joints move in many directions. The
main joints of the body—found at
the hips, shoulders, elbows, knees, wrists, and ankles—are freely movable.
They are filled with synovial fluid, which acts as a lubricant to help the
joints move easily.
According to their movements, synovial joints may be classified as the
following:
1. Gliding joints – These joints permit side-to-side and back-and-forth
movements. An example is the wrist joint.
2. Hinge joints – These joints
allow only back-and-
forth movements such as
bending and straightening.
Examples are elbow joints
and knee joints.
3. Pivot joints – These joints
allow rotational movement
pivot joint
only. An example is the hinge joint
joint between the bones in
the forearms.
4. Ball-and-socket joints –
These joints permit side-
gliding joint
to-side, back-and-forth,
and rotational movements. ball-and-socket joint
Examples are shoulder and
hip joints. The synovial joints
10 Smart Science 4

17. The bones in synovial joints
ligamentum flavum
are held together by ligaments.
intertransverse
A ligament is a tough band of facet
ligament
capsulary
white, slightly elastic tissue. ligament
It binds the bones together to posterior
longitudinal
prevent dislocation. Ligaments interspinous
ligament
ligament
also support some internal anterior
organs like the bladder and supraspinous longitudinal
liver. ligament ligament
Knowing the parts of your Ligament
skeletal system will make you
understand better how to take good care of it.
Home Economics
Bulalo, a Filipino dish that originated from Batangas, is a very tasty soup whose
main ingredient is the kneecap of a cow. Contrary to popular belief that one eats the brain
of the cow in bulalo, what you actually find inside the kneecap is the marrow—a kind of
soft tissue that is responsible for the storage of fats.
Keep in Mind
• The skeletal system is the framework of the human body. It is made up
of bones that give support, shape, and protection to the body.
• The skeletal system is divided into two groups: axial and appendicular
skeletons.
• The axial skeleton consists of the skull, the backbone, and the rib cage.
The appendicular skeleton consists of the bones of the appendages
(arms, hands, legs, feet) and the girdles (pectoral and pelvic).
• The outer layer of the bone is called the compact bone. It forms the
protective outer part of all bones.
Human Body Systems: Skeletal, Muscular, and Digestive 11

18. • The inner layer of the bone is called the spongy bone. The spaces
between the spongy bone are filled with blood and red marrow.
• Cartilage is a tough, semi transparent, elastic tissue that covers
the surface of joints. A joint is a point where two bones meet.
• Joints allow your body to move in many ways. Joints can be freely
movable, partially movable, or immovable.
• A ligament is a tough band of white, slightly elastic tissue that binds the
bone together to prevent dislocation.
Challenge Yourself
Write T on the blank space if the statement is true. If it is false, change
the underlined word or phrase to make the statement true.
__________ 1. The skeleton is the framework that supports and protects
the body.
__________ 2. The bones of the legs are part of the axial skeleton.
__________ 3. The bones of the feet support the weight of the entire body.
__________ 4. An adult person has 206 bones. Of these, 22 bones form
the rib cage.
__________ 5. The rib cage protects the heart and the lungs.
__________ 6. The yellow marrow repairs the hard layer of the bone.
__________ 7. Vitamin C helps the bone absorb calcium.
__________ 8. Hinge joints permit side-to-side, back-and-forth, and
rotational movements.
__________ 9. Like the immovable joint, the knee joint can be bent or
straightened.
__________10. Pivot joints allow rotational movement only.
12 Smart Science 4