The circulatory system transports blood, nutrients, oxygen, and waste throughout the body using the heart, blood vessels, and blood. The heart pumps blood through arteries and veins to all parts of the body. Blood contains plasma, red blood cells that carry oxygen, white blood cells that fight infection, and platelets that help blood clotting.

1. Smart Science 6
Textbook

2. Smart Science
GRADE 6
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: 978–971–46–0095–9
REVIEWER
Marina 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 Body Systems
Chapter 1 The Circulatory System
Lesson 1 Parts of the Circulatory System and Their Functions ....................................2
Lesson 2 Pathway of Blood ......................................................................................11
Lesson 3 Some Diseases Affecting the Circulatory System........................................14
Lesson 4 Caring for Your Circulatory System ...........................................................19
Think Back .................................................................................................................23
Measure Up! .................................................................................................................23
Chapter 2 The Nervous System
Lesson 1 Nervous System: Control Unit of the Body ................................................25
Lesson 2 Parts of the Nervous System and Their Functions ......................................29
Lesson 3 How Messages Travel ...............................................................................34
Lesson 4 Body Responses to Stimuli ........................................................................38
Lesson 5 Some Disorders and Diseases Affecting the Nervous System .....................42
Lesson 6 Caring for Your Nervous System ...............................................................46
Think Back .................................................................................................................51
Measure Up! .................................................................................................................51
Unit 2 The Ecosystem
Chapter 3 Relationships among Organisms
Lesson 1 Relationships in the Ecosystem ..................................................................54
Lesson 2 Producers and Consumers.........................................................................59
Lesson 3 Food Chain and Food Web .......................................................................64
Lesson 4 Decomposers ............................................................................................68
Lesson 5 Nutrient Cycles .........................................................................................71
Think Back .................................................................................................................76
Measure Up! .................................................................................................................76
Chapter 4 The Environment
Lesson 1 Effects of Deforestation .............................................................................79
Lesson 2 Destructive Human Activities ....................................................................85
Lesson 3 Preservation and Conservation of Our Ecosystem ......................................90
Think Back .................................................................................................................93
Measure Up! .................................................................................................................93

5. Unit 3 Matter, Energy, and Motion
Chapter 5 Matter Everywhere
Lesson 1 The Nature of Matter .................................................................................96
Lesson 2 Properties of Matter.................................................................................100
Lesson 3 Elements .................................................................................................106
Lesson 4 Compounds and Mixtures .......................................................................110
Lesson 5 Common Household Materials and Their Uses .......................................116
Lesson 6 Technology Improves Materials ..............................................................120
Lesson 7 Harmful Effects of Materials ....................................................................123
Lesson 8 Proper Usage and Storage of Materials ....................................................127
Lesson 9 Proper Disposal of Materials ...................................................................130
Think Back ...............................................................................................................134
Measure Up! ...............................................................................................................135
Chapter 6 Energy around Us
Lesson 1 Mechanical Energy..................................................................................137
Lesson 2 Electrical Energy .....................................................................................141
Lesson 3 Chemical Energy .....................................................................................145
Lesson 4 Radiant Energy ........................................................................................148
Lesson 5 Sound Energy ..........................................................................................152
Lesson 6 Energy Transformation and Transfer ........................................................155
Think Back ...............................................................................................................157
Measure Up! ...............................................................................................................158
Chapter 7 Force and Motion
Lesson 1 Forces in Motion………………………………………………….. ......................160
Lesson 2 Speed……………………………………………………………… .........................164
Lesson 3 Velocity…………………………………………………………… ........................169
Think Back ……………………………………………………………………. ...........................171
Measure Up! ……………………………………………………………………. ...........................172
Unit 4 Earth, Our Home
Chapter 8 Solid Earth
Lesson 1 Layers of Earth ........................................................................................174
Lesson 2 Movement on Earth’s Crust .....................................................................178
Lesson 3 Earthquakes ............................................................................................184

6. Lesson 4 In Case of an Earthquake .........................................................................189
Lesson 5 Volcanoes and Volcanic Eruptions ..........................................................193
Lesson 6 Effects of Volcanic Eruptions ...................................................................198
Lesson 7 Awareness of Volcanic Eruptions ............................................................202
Think Back ...............................................................................................................206
Measure Up! ...............................................................................................................207
Chapter 9 Weather and Climate
Lesson 1 Factors Affecting Weather and Climate ...................................................209
Lesson 2 Seasons on Earth .....................................................................................216
Lesson 3 Seasons in the Philippines .......................................................................223
Lesson 4 Effects of Weather and Climate ...............................................................227
Think Back ...............................................................................................................231
Measure Up! ...............................................................................................................231
Unit 5 Beyond the Solar System
Chapter 10 All about Stars
Lesson 1 Stars and Their Characteristics .................................................................234
Lesson 2 Life Stages of a Star .................................................................................241
Lesson 3 Constellations .........................................................................................245
Lesson 4 Using Telescopes to Learn More about Stars ...........................................249
Lesson 5 Our Sun, a Star .......................................................................................255
Think Back ...............................................................................................................259
Measure Up! ...............................................................................................................260
Chapter 11 Galaxies and the Universe
Lesson 1 Galaxies ..................................................................................................261
Lesson 2 Studying the Universe .............................................................................265
Lesson 3 Space Exploration ...................................................................................271
Think Back ...............................................................................................................275
Measure Up! ...............................................................................................................276
Glossary ...............................................................................................................277
Bibliography ...............................................................................................................280
Index ...............................................................................................................281

7. Unit 1
Body Systems
Did you know that the human body is similar to a machine? In fact, the human
body is often considered as a complex machine as it is composed of several machines.
For example, the heart is a “pump,” the eye is a “camera,” the stomach is a “food
processor,” and the brain is a “computer.” Each of these machines is composed of parts.
These parts differ in size and in shape, but all of them work together to accomplish their
main goal. And just like machine parts, several of the body parts can now be changed if
they get defective—thanks to modern technology.

8. Chapter 1
The Circulatory System
You have already learned the parts and functions of the reproductive system, the
urinary system, and the respiratory system. These body systems play vital roles for our
survival. This chapter will introduce you to the circulatory system, which is responsible
for transporting nutrients and oxygen, and collecting wastes in your body.
Lesson 1
Parts of the Circulatory System
and Their Functions
Find Out
1. How do you compare the circulatory system with a train system?
2. How does the circulatory system function?
3. What are the parts of the circulatory system?
4. What is the function of each part?
Each day, about 2 000 gallons of blood travel many times in your blood vessels.
Blood is sent throughout your body with each heartbeat.
The circulatory system or cardiovascular system is often described as the “lifeline”
of the human body. When the food you have eaten is digested and turned into simpler
materials, these are absorbed by the tiny blood vessels of the small intestine. These
simple materials are then used by the cells of the body. But how do the materials reach
all the cells throughout the body?
The activity on the next page will help illustrate the similarity of a train system to
the circulatory system.
2 Smart Science 6

9. Analyzing a Train System
Look at the diagram of a train system. Answer the following questions on a
separate sheet of paper.
Routes of LRT Line 1 and LRT Line 2
1. What do the circles represent? How do they function?
2. How are people transported by the train system?
3. Compare the train system with the circulatory system in terms of being a
a. pick up system
b. delivery system
4. What happens if a train system fails?
Body Systems 3

10. A train system is like the circulatory system.
A train transports people to different places. People are picked up at certain points
and brought to other points in the train system. Blood circulates in the body in a similar
manner.
The circulatory system is made up of the heart, blood vessels, and blood. The
circulatory system takes care of the distribution of nutrients and oxygen picked up
by the blood to the different parts of the body. It transports and delivers nutrients to
all cells. It also collects waste materials produced by the cells and brings them to the
organs in charge of eliminating wastes from the body.
Heart
The human heart is a muscular organ about the size of a clenched fist. The heart
is inside a protective sac called the pericardium. Made up of strong muscles, the heart
receives and pumps blood. The heart is the “blood pump” of the body. It sustains the
flow of blood throughout the body.
Language
Many scientific terms form their plural irregularly. For instance, some words ending
in -ium or -um are made plural by changing this ending to -ia. For example, atrium – atria;
septum – septa; pericardium – pericardia; and bacterium – bacteria. Note that not all words
ending in -ium can be made plural this way. Exceptions include elements such as sodium,
calcium, and barium.
Research other scientific words that form their plural irregularly and familiarize yourself
with them.
Check IT out!
The Jarvik-7 artificial heart is named after
its American physician designer, Robert K. Jarvik.
The Jarvik-7 has two pumps, each with a disk-
shaped mechanism that pushes the blood from the
inlet valve to the outlet valve.
Visit the following Web sites for more
information on the artificial heart:
http://inventors.about.com/library/inventors/
blartificialheart.htm
http://sln.fi.edu/biosci/healthy/fake.html Jarvik-7
4 Smart Science 6

11. The heart is hollow and
divided down the middle into superior vena cava
aorta
a left side and a right side by
a wall of muscle called the pulmonary
septum. Each side of the heart artery
is further divided into the pulmonary
valve
upper and the lower chambers. veins
The upper chamber is called left atrium
the atrium (also called the
auricle); the lower chamber is right atrium
called the ventricle. Both the left ventricle
right ventricle
left and the right sides of the
septum
heart pump blood through the inferior vena
chambers at the same time. cava
The right side pumps blood to
the lungs. The left side pumps The parts of the heart. The arrows indicate the direction of
blood into the different parts of the blood flow.
the body.
Connected to the heart are arteries and veins where blood going to and coming
from various parts of the body passes through. The aorta, the largest artery in the body,
is directly connected to the heart. It branches into smaller arteries which further branch
out into smaller blood vessels. From the heart, oxygenated blood passes through the
aorta to the different parts of the body. There are also two large veins called vena cavae
(singular: vena cava). One of them is the superior vena cava. It carries blood from the
head, the arms, and the rest of the upper trunk to the heart. The inferior vena cava, on
the other hand, carries blood from the lower part of the body to the heart. From the
different body parts, the two vena cavae pass the blood to the right atrium. Pulmonary
veins and arteries are also connected to the heart. They connect the heart to the lungs.
The heart has two doorlike valves which direct the flow of blood in one direction.
The valves prevent oxygenated blood from mixing with deoxygenated blood.
What can be done when parts of the heart malfunction? Scientists have devised
medical procedures and inventions to help people with heart problems. The artificial
heart, artificial pacemaker, and artificial valves are some of the inventions that help
people suffering from heart ailments and/or valve malfunctions. When a person’s veins
and arteries get clogged, he or she is advised to undergo a heart bypass operation.
Blood
Blood is the liquid component of the circulatory system. Blood circulates
throughout the body carrying nutrients needed for the growth and normal function of
the body cells. Have you seen blood? Do the activity in Explore and observe a prepared
blood smear under the microscope.
Body Systems 5

12. A Look at a Human Blood Sample
You will need a compound microscope and a prepared slide with a drop of
human blood.
1. Put the microscope on a sturdy, flat table. Make sure that the microscope receives
enough light. Mount the prepared slide with a drop of human blood on the
microscope’s stage. Use the stage clips to hold the slide.
2. Focus the objectives properly to get a clear view of the sample. Use the low-
power objective (LPO) first and then the high-power objective (HPO).
3. Observe what you see under the LPO and the HPO.
4. Describe how blood looks under both the LPO and the HPO.
5. Draw the blood as seen under the LPO and the HPO on a sheet of paper.
From the activity, you have observed that blood has different components. Blood
is actually made up of plasma, red blood cells, white blood cells, and platelets. You
will learn more about these components in Table 1.1 below.
Table 1.1 The Components of Blood
Component Description Image
Red blood cells • These are constantly
(RBC) produced by the bone
marrow.
• These contain hemoglobin—
the iron and oxygen carrier
of the blood. Iron is a
mineral needed by the body.
Hemoglobin that combines
with oxygen gives blood its
Red blood cells
red color.
6 Smart Science 6

13. Component Description Image
White blood cells • These are mostly formed in
(WBC) the bone marrow.
• These are bigger than red
blood cells.
• These are called the “soldiers
of the body” for they fight
foreign bodies that cause White blood cells
diseases and infections.
Platelets • These are minute discs
(smaller than red blood cells)
that produce substances
needed for blood to clot.
Clotting prevents blood loss.
Platelets
Plasma • This is the yellowish liquid
portion of the blood.
• This is composed of 90%
water and 10% dissolved
nutrients, proteins, minerals,
Plasma cell
salts, and waste products.
• This transports nutrients to
the cells and carries waste Plasma
materials.
As blood flows, it exerts pressure on the walls of the arteries.
The exertion of pressure on the walls of the arteries by the
blood is known as blood pressure. Blood pressure
is determined by factors such as the strength
of the heart muscles, amount of blood in
the cardiovascular system, and condition
of the arteries. Human blood pressure
is measured by an instrument called
sphygmomanometer. The normal blood
pressure among adults is 120/80 (read
as “120 over 80”). The first number
(120) is called systolic pressure, while Sphygmomanometer
Body Systems 7

14. the second number (80) is called diastolic pressure. Systolic pressure refers to blood
pressure while the heart contracts. Diastolic pressure, on the other hand, refers to
blood pressure while the heart relaxes. You will learn more about the effects of high
blood pressure and other circulatory diseases in Lesson 3 of this chapter.
Blood Vessels
Where does blood pass through? Blood flows through a network of tubes in the
body called blood vessels. Do the following activity to know more about them.
A Look at Blood Vessels
You will need a handy face mirror.
1. Look closely at the mirror. Observe the white portion of your eye. What do you
see?
2. Look at the underside of your tongue. Describe what you see.
3. Why are certain blood vessels reddish while others are bluish?
4. Make a tight fist with your left hand. Then, using your right hand, grasp your left
wrist tightly. After a minute, stretch your left palm.
Caution: This step should not be done if you bruise easily. You can observe your
classmate’s palm instead.
a. Did the color of the your palm’s skin change? What could have caused this?
b. What are the functions of blood vessels in our body?
The bluish and reddish lines you see beneath your skin are blood vessels.
Arteries, veins, and capillaries are all blood vessels.
8 Smart Science 6

15. Thick-walled and elastic, the arteries carry blood that contains nutrients and
oxygen away from the heart. Their thick walls enable them to withstand the pressure of
blood flow. Arteries branch out into arterioles and then into much smaller capillaries.
Other capillaries are connected to the venules, which in turn, are connected to the
veins.
membrane
valve
connective
capillary
muscle tissue
connective vein
tissue
artery
venule
arteriole
The blood vessels
Veins are elastic and are larger in diameter compared to the arteries; however,
they have thinner walls. The pressure of the blood flow along the veins is not as great as
that in the arteries. Pulmonary veins transport oxygenated blood from the lungs to the
heart. All other veins carry deoxygenated blood from the organs back to the heart.
The smallest blood vessels are the capillaries. Oxygen and nutrients in the blood
pass through the walls of the capillaries into the cells, while cellular wastes pass from
the cells through the capillary walls then into the blood, making the exchange of
nutrients and waste materials possible.
To summarize, blood coming from the heart flows through the blood vessels in
this order: from the arteries, arterioles, capillaries, venules, veins, and back to the heart.
These blood vessels form a network that allows the blood to circulate throughout the
body.
Check IT out!
Vital signs are checked and monitored using the
electrocardiograph. It is a machine used to monitor the heartbeat
by attaching electrodes to a person’s body. Abnormalities in the
hearbeat could be an indication of a heart problem.
An electrocardiograph
Body Systems 9

16. Keep in Mind
• The human circulatory system is a transport system. It is responsible for
distributing nutrients to cells, collecting waste materials produced by the cells,
and depositing them to specific excretory organs.
• The circulatory system has three main components: heart, blood, and blood
vessels.
• The right side of the heart pumps blood to the lungs while the left side pumps
blood to the different parts of the body.
• Blood is the liquid component of the circulatory system. It has four components:
plasma, red blood cells, white blood cells, and platelets.
• Blood flows through a network of tubes called blood vessels. Veins, arteries, and
capillaries are blood vessels.
Challenge Yourself
Answer the following briefly.
1. List two major functions of the circulatory system.
a. _________________________________________________________________
_________________________________________________________________
b. _________________________________________________________________
_________________________________________________________________
2. Explain how blood flows through the blood vessels.
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
10 Smart Science 6