LOWER SECONDARY SCIENCE TEXTBOOK

5.3 Organisation of Cells

You should be able to:
• recognise that cells are organised to form tissues, organs

and systems in multicellular organisms;
• identify the organs in the main body systems found in

human beings;
• state the main functions of the digestive system, transport

system, respiratory system and reproductive system.

Cells

Some organisms are made up of only one cell. These
are known as unicellular organisms. An example of a
unicellular organism is the paramecium.

Paramecium

However, most organisms — including human beings and
plants — are made up of many cells. They are known
as multicellular organisms. The cells in multicellular
organisms are designed to have specif ic functions.

Cells found in a leaf Cells found in an animal

99Cell Structure and Organisation

Tissues

Cells of the same kind that perform the same function are
grouped together to form a tissue.

The heart muscle is made up of cells The epidermal tissue is made up of
that are grouped together to form many closely packed cells.
heart muscle tissue.

Organs

Several tissues working together to perform a specialised
function form an organ.

The heart is an organ formed by A leaf is made up of many tissues
muscle tissues, nerve tissues and including the epidermal tissues.
connective tissues. It pumps blood They form the outermost layer of
to all the cells in the body. the leaf.

100 Cell Structure and Organisation

Systems Science Bites
The shoot system of a
Organs work together to form systems. Four fl owering plant provides
examples of systems in the body are the digestive support for the plant
system, transport system, respiratory system structure and allows
and reproductive system. nutrients and water to travel
throughout the plant.
Digestive system
The function of the digestive system is to break Shoot
down food into simpler substances that the body system
can absorb.

Mouth
Salivary

glands

Oesophagus

Liver Stomach
Gall bladder Pancreas

Small intestine

Large intestine

Rectum
Anus
Some parts of the digestive system

WB Link Activity 5.4

101Cell Structure and Organisation

Transport system
The function of the transport system is to transport blood
which carries digested food and oxygen to all parts of the
body. It also transports carbon dioxide and other waste
products from all parts of the body to the excretory organs.

Heart

Blood vessels

Some parts of the transport system

Respiratory system
The function of the respiratory system is to supply blood
with oxygen. This oxygenated blood is then transported to
all parts of the body by the transport system.

Science Bites Nostrils Trachea
As we breathe in, air Oxygen from the
Fish do not have enters the nostrils lungs moves into the
lungs. Instead, they and mouth. It travels blood. Carbon dioxide
breathe through gills. down the trachea and from the blood moves
into the lungs. into the lungs.

Lungs
Carbon dioxide moves
out of the lungs, up
the trachea and is
breathed out through
the nostrils.

Some parts of the respiratory system

102 Cell Structure and Organisation

Reproductive system
The reproductive system consists of organs involved in
sexual reproduction. The following are the organs found in
the male and female reproductive systems.

Sperm duct Penis
Testes

Parts of the male reproductive system

Oviduct
Ovary

Uterus
Vagina

Parts of the female reproductive system

?

What will happen to your body if one of the organ systems
fails to function?

Quick Check

1. What are tissues made up of?
2. Name the four systems present in our body.
3. State the function of the respiratory system.

103Cell Structure and Organisation

Summary

Cells

are tiny and can only can be group to
be viewed with a classifi ed as form

Microscope Plant cells Animal cells Tissues
group to
which has the which which form
following parts have have
Organs
Mirror group to
form
Stage Cytoplasm
Systems

Large knob Nucleus small and • Digestive
Small knob large numerous or system
Eye piece none at all
Objective lenses Vacuole • Transport
system
Cell
membrane • Respiratory
system

• Reproductive
system

Tube Cell wall group to
Clips Chloroplast form

Multicellular
organisms

104 Cell Structure and Organisation

Review Questions

1 Identify the part of the plant cell in which chloroplasts are found.

A Vacuole
B Nucleus
C Cell wall
D Cytoplasm

2 What is the function of the nucleus in a cell?

A It is a thin membrane that surrounds the cell.
B It is a place where all chemical reactions take place.
C It protects the cell and gives the cell a regular shape.
D It controls cell activities and is needed for the cells to reproduce.

3 Which structure is present in both plant and animal cells?

A Cell wall
B Chloroplast
C Cell membrane
D A large vacuole

4 The table below shows the different cell parts of four types of cells:
W, X, Y and Z. The tick (✓) indicates the cell parts that can be found in
each cell.

Cell parts WX Y Z
Cell wall ✓✓
Nucleus ✓ ✓✓
Chloroplast ✓

Which of the following best represents W, X, Y and Z?

W XY Z

A Cheek cell Root cell Red blood cell Cactus stem cell

B Cactus stem cell Red blood cell Root cell Cheek cell

C Red blood cell Hydrilla leaf cell Onion cell Cheek cell

D Cactus stem cell Cheek cell Onion cell Root cell

5 Name the structure that is made up of a group of cells performing a
similar function.

A A tissue
B A system
C An organ
D A multicellular organism

105Cell Structure and Organisation

6 Which of the following belongs to the human respiratory system?
A Trachea
B Stomach
C Small intestine
D Large intestine

7 Which is the path taken by air as we inhale?
A Nose  Lungs  Trachea
B Lungs  Trachea  Nose
C Nose  Trachea  Lungs
D Mouth  Lungs  Trachea

8 Identify the following parts of the microscope and state their functions.

D

AE
B

F
CG

H

106 Cell Structure and Organisation

9 The pictures below show two cell specimens, A and B, as seen through
a microscope. Which specimen is obtained from a plant and which from
an animal? Give 2 reasons for your answer.
AB

10
A
B

CF
D
E

a) Identify structures A, B, C, D, E and F.
b) Which labelled structure A, B, C, D, E or F in the diagrams above:

i. is needed for the cell to stay alive?
ii. is needed to make food during photosynthesis?
iii. gives the cell its regular shape?
iv. controls substances entering or leaving the cell?
v. is a large space f illed with liquid?
11 Name the body system that:
a) allows us to breathe,
b) ensures the continuity of the species,
c) breaks down food into simpler substances, and
d) carries food and oxygen to all parts of the body.

107Cell Structure and Organisation

12 The f igure below illustrates different levels of organisation in a
squirrel’s body. Identify the parts labelled using the words given in
the box.
Digestive system Cell Organ Tissue Organism

A
C

B D
E
13 Identify the following parts of the digestive system.

A
B
C

D

108 Cell Structure and Organisation

Chapter Force and

6 Pressure

Have you ever wondered why large vehicles have many large
wheels? This is because large vehicles are heavy. Their weight
exerts a great force on the ground. A force acting on a larger area
of contact produces a lower pressure than the same force acting
on a smaller area. Therefore, with many large wheels, the force
exerted by the heavy vehicle can be spread over a larger area. In
this chapter, you will learn more about force and pressure.

Firman Allah Subhanahu Wa Ta’ala
Tafsirnya:
Dan Dialah yang telah menciptakan
Malam dan Siang serta Matahari dan
Bulan, masing-masing beredar di tempat
peredarannya. (33)

And He it is Who has created the Night
and the Day, and the Sun and the Moon,
each in an orbit floating. (33)

(Surah al-Anbiya: 33)

Let’s Explore

• What is a force?
• What is pressure?
• How do we calculate pressure?
• What is work done?

Force and Pressure 109

6.1 Forces

You should be able to:
• state that a force is a push or a pull;
• identify the different types of forces (e.g. force of gravity,

friction and magnetic force).

A force can be a push or a pull. A force can also be a
combination of a push and a pull e.g. bending and twisting.
Some examples of forces in our daily life are shown below.

Push Pull Lift

Bend Twist and squeeze Stretch
Examples of forces

Forces acting around us include the force of gravity,
friction and magnetic force.

110 Force and Pressure

Force of gravity Super Scientist

When you drop a ball, it falls towards the ground. This is
because the Earth exerts a pulling force on the ball. This
force is called the force of gravity.

The ball falls to the ground due to the force of gravity. Sir Isaac Newton
was the scientist who
The weight of an object is the force of gravity acting on discovered gravity.
it. Your body’s weight is due to the force of gravity acting He gave a lot of
on you. thought to the simple
However, the force of gravity acting on an object on the event of an apple
Moon is weaker than on Earth. So, the weight of the same falling to the ground.
object will be less on the Moon. He suggested that
there is a force that
pulls all objects
towards the ground.
This force is called
the force of gravity.

Science Smart

Mass is a measure
of the amount of
matter in a body.
The weight of an
object is the force of
gravity acting on it.

Your weight will be less on the Moon than on Earth.

Force and Pressure 111

Importance of gravity in our daily lives
Gravity is an important part of our everyday lives but you
probably don’t even notice it is there. Here are some examples
of how gravity affects us.
Gravity is the reason why we do not f loat away into space. It
pulls us down towards the ground (towards the centre of the
Earth). This pulling effect enables us to walk, run, jump and play
without f loating up into the air. Gravity also enables all the things
around us to stay in place. This includes plants and animals, and
even the food on our plates!

Gravity keeps us from floating away into When you kick a football, it
space when we jump up into the air. always falls back to the ground
because of gravity.

The Earth’s gravity also keeps the Moon in its place. Without
gravity, the Moon would f loat away into space.

112 Force and Pressure Gravity pulls the Moon towards Earth.

Friction

Why is it difficult to push a wooden crate over a rough floor?
There is an opposing force between the rough floor and
the wooden crate. This force is known as friction. It acts
when one material rubs against another. Different surfaces
produce different amounts of friction.

Rough surfaces produce more friction. Smooth surfaces produce less friction.

Importance of friction in our daily lives
Friction can be a useful force in our everyday lives. The
following examples show some uses of friction.

Without friction between the ground Friction helps to keep the wheels of a car on the
and our feet or shoes, we would not road and slows the car when brakes are applied.
be able to walk without slipping.

Drivers should drive slowly in rainy weather. Do you
know why?

Force and Pressure 113

Disadvantages of friction
Friction can also be a nuisance. Have you ever had to replace
your shoes because the soles have worn out? This is due
to the friction between the soles and the f loor. Constant
friction leads to wear and tear.

Rubber pads of bicycle brakes and soles of shoes are worn out due to friction.

Friction causes moving parts of machinery to wear out. It
also produces a lot of heat.

Try this

An eraser uses
friction to remove
markings from paper.
Rub your eraser on
a sheet of paper.
Can you feel a force
making this diff icult?
This force is known
as friction. Is the tip
of the eraser warm?

Friction between the wall and a drill bit produces a large
amount of heat.

114 Force and Pressure

Ways to reduce friction
We have seen how friction is useful, as well as a problem,
in our daily lives. Friction can cause damage to surfaces.
The heat given out during friction is a waste of energy.
To reduce friction, and thus reduce wear and tear, we use
wheels, ball bearings, lubricants and even air between
interacting surfaces.

Inline skates use wheels to Engine oil lubricates the moving parts in
reduce friction. a car engine.

A hovercraft uses a cushion of air to reduce friction.

WB Link Activity 6.1

Force and Pressure 115

Magnetic force

Magnetic force, or magnetism, is the force of attraction or
repulsion exerted by magnets or magnetic materials such
as iron and steel. Every magnet has a North pole and a
South pole.

NS

The ends of a magnet have magnetic force.

The North pole of a magnet will repel the North pole of
another magnet. The force acting between these magnets is
called the force of repulsion.

S NN S

Like poles of magnets repel each other.

On the other hand, the North pole of a magnet will attract
the South pole of another magnet. The force acting between
these magnets is called the force of attraction.

S NS N

Unlike poles of magnets attract each other.

116 Force and Pressure

Importance of magnetic force in our daily lives
Magnetic force is used in our daily lives. Let us look at a few
examples of how this force is useful to us.

Magnetic buttons are used Magnetic doorstoppers are
to hold notes and reminders used to hold doors open.
on refrigerator doors.

Handbags and pouches have magnetic fasteners to open and close them.

Quick Check Link It

1. Name three types of forces. Magnets have many
2. Give two uses of friction. uses in our daily lives.
Learn more about
magnets in chapter 8.

Force and Pressure 117

6.2 Effects of Forces

You should be able to:
• describe the effects of a force on a body at rest or in

motion with respect to changes in speed, direction, size
and shape.
We cannot see a force. However, we can see its effects on
the objects it acts upon. When a force acts upon an object,
the following effects may be observed.

A force can change the speed of an object

A force can either increase or decrease the speed of
an object. For example, pushing harder on the pedals of
a bicycle speeds it up. Pressing the hand brake of a bicycle
slows it down. A force can also stop a moving object.

A cyclist increasing his speed

Pressing hard on the hand brakes of a bicycle can stop the bicycle.

118 Force and Pressure

A force can change the direction of a
moving object

A force can change the direction in which an object is
moving. For example, when a football player kicks a moving
ball, it may change direction.

The force exerted by the kick changes the direction of the ball.

Sail boats rely on the wind to move. The force exerted by
the wind allows the sail boat to move or change its direction.

The wind exerts a force that can move or change the direction
of a sail boat.

Force and Pressure 119

A force can change the size and shape of
an object

A force can cause an object to change in size.

When air is blown into a balloon, it exerts When a force is applied to an aluminium
a force that causes the balloon to expand. can, it can be flattened and made smaller.

A force can also cause an object to change in shape.

When we press plasticine, we are applying A sponge changes in shape when squeezed.
a force that causes its shape to change.

Activity 6.2 Quick Check

WB Link Activity 6.3 1. List the effects of forces.
2. Give 5 examples of forces.

120 Force and Pressure

6.3 Measurement of
Forces

You should be able to:
• measure force using a spring balance;
• state newton (N) as the S.I. unit of force.
The S.I. unit for force is newton (N). A spring balance can
be used to measure the size of a force.

A kitchen scale is an example of a
spring balance

Link It

You have learnt about mass and the beam
balance in Chapter 1. Since the weight of
an object depends on its mass, most spring
balances read in kilograms instead of newtons.

Quick Check

1. Which instruments can be used to measure force?
2. What is the S.I. unit of force?

Force and Pressure 121

6.4 Work Done

You should be able to:
• def ine work done;
• calculate work done;
• state the unit of work done.

Work is done when an object moves while a force is being
exerted on it. For work to be done, the following conditions
are required:
1. There is a force acting on an object.
2. The object moves.
3. The movement of the object is in the direction of

the force.

Force is applied Object moves
on the object.

Object moves
in the direction
of the force.

Conditions for work to be done

If any of these three conditions is missing, then no work is
done.

=1U sk1ei,l0ofuj0ol0uc lJoe n(vkeJ)rsions Calculating work done
=1=1 m0m1.,ie00llg0i0ja1o0ju ,oJ0lue0l e0(m (JMJ)J)
Work done is calculated by the following formula:
Work done = Force × Distance moved in the
direction of the force

The S.I. unit of work done is joule (J). This is also the unit
for energy.

122 Force and Pressure

Let us look at some examples to show how work done
is calculated.
Example 1
Siti carries a 80 N school bag up a f light of stairs, 3 m high.
Calculate the amount of work done against gravity to carry
the school bag upstairs.
Work done = Force × Distance moved

= 80 N × 3 m
= 240 Nm
= 240 J

Example 2
Mariah lifts a 50 N weight to a height of 1 m from the f loor.
Calculate the amount of work done.
Work done = Force × Distance moved

= 50 N x 1 m
= 50 Nm
= 50 J

Example 3
600 J of work was done lifting a 400 N load. How high was
the load lifted?
Work done = Force × Distance moved
Distance moved = WoFrokr dceone

= 460000 NJ
= 1.5 m

Quick Check

1. What is work done?
2. What are the conditions required for work done?
3. What is the S.I. unit of work done?

Force and Pressure 123

6.5 Pressure

You should be able to:
• define pressure as force per unit area;
• relate pressure to force and area and calculate pressure

using the equation: Pressure = FAorrecae;
• state that the S.I. unit of pressure is newton per square

metre (N/m2) or pascal (Pa).

Pressure is defined as the amount of force acting per
unit area. The S.I. unit of pressure is newton per square
metres (N/m2) or pascal (Pa).

Pressure depends on the amount of force used and the area
of contact. A force acting on a small area of contact produces
a greater pressure than the same force acting on a larger
area.

For example, push a sharp pencil and a blunt pencil into an
eraser. Remember to use the same amount of force both
times. You will notice that the sharp pencil goes deeper into
the eraser compared to the blunt pencil. Because it has a
sharp tip, a smaller surface area comes into contact with
the eraser. As the surface area is smaller, the pressure is
greater, thus allowing the pencil to go deeper. Likewise,
because the blunt pencil has a tip with a bigger surface
area, it exerts less pressure on the eraser and thus does
not poke in as deeply.

Sharp pencil Blunt pencil

A greater pressure is produced by the sharper pencil.

124 Force and Pressure

Calculating pressure

Pressure is calculated by the following formula:
Pressure = FAorrecae

Force is measured in newtons and area is measured in square
metres. Thus, pressure is measured in newtons per square metres
(N/m2).

Let us look at the following examples of how to calculate pressure.

Example 1
An elephant and a lady stand on a floor. The lady’s shoes have
sharp heels.

Which will damage the floor more — the elephant or the heel
of the lady’s shoe? The elephant exerts a greater force, as it is
heavier. But the area of the lady’s heel is less than the elephant’s
foot. To answer our question, let us do some calculations.

Elephant:
Take the weight of the elephant as 40 000 N and the area of its
foot as 1 000 cm2.

Pressure = FAorrecae
= 14 00 0000 0cm N2
= 40 N/cm2

Lady:
Take the weight of the lady as 400 N and the area of the shoe
heel as 1 cm2.

Pressure = FAorrecae
400 N
= 1 cm2

= 400 N/cm2

The pressure exerted by the shoe heel is ten times greater. The
sharp heel will damage the floor more than the elephant will.

Force and Pressure 125

Example 2
A wooden block weighs 2 000 N. It has dimensions of 4 m ×
1 m × 0.2 m. What is the pressure exerted by the wooden
block on the ground when it is laid:

4 m

0.2 m
1 m

a) on its largest surface? b) on its smallest surface?

a) Area of largest surface = 4 m × 1 m = 4 m2

Pressure on largest surface = FAorrecae
2 000 N
= 4 m2

= 500 N/m2
= 500 Pa

b) Area of smallest surface = 0.2 m × 1 m = 0.2 m2

Pressure on smallest surface = FAorrecae
2 000 N
= 0.2 m2

= 10 000 N/m2
= 10 000 Pa

WB Link Activity 6.4 The smaller surface of the wooden block, when in contact
with the ground, produces the larger pressure.

126 Force and Pressure

Applications of pressure

Here are some examples of how we use pressure.
The studs on football boots decrease the area of contact
with the ground. This increases the pressure, causing the
studs to easily sink into the ground, thus preventing the
player from slipping.

Studs increase pressure on the ground.

A bulldozer uses steel tracks that have a large surface
area. Although the bulldozer is heavy, its weight is spread
over a large area, so the pressure on the ground is
small. Therefore, the bulldozer does not sink easily into
mud or sand.

Quick Check

1. What is pressure?
2. What is the S.I. unit

of pressure?
3. What is the formula for

calculating pressure?

A bulldozer’s weight is spread over a large area.

Force and Pressure 127

Summary

Forces

defi ned as can be of cause the measured Applications
many types following in
effects

Work done Pressure

A push Newtons (N) Pressure
or pull = FAorrecae
Change in speed S.I. unit
Change in = N/m2 or Pa
direction Work done =
Force × Distance
Change in size moved
Change in shape
S.I. unit
= joule (J)

Force of gravity
Friction

Magnetic force

Quantity Unit Symbol
Force newton N
Work done joules J
Pressure pascal Pa

128 Force and Pressure

Review Questions

1 If you give a book a sharp push along a table, it will move a short
distance before slowing down to a stop. What causes the book to
stop moving?

A The force of gravity pulls it down.
B There is air resistance between the book and the table.
C There is a frictional force between the book and the table.
D There is an electrical force generated between the book and

the table.
2 When you throw a basketball upwards, it will fall back downwards.

Which of the following is true?
A No force acts on the ball, hence the ball slows down.
B The ball falls back to the ground due to the force of gravity.
C The ball was not thrown with enough force to prevent it from

slowing down.
D A force in the air causes the ball to fall faster towards the ground.

3 Which one of the following causes your shoes to wear out?
A Weight
B Friction
C Pressure
D Polishing

4 Which of the following effects cannot be observed when you kick a
moving ball?

A The ball gets bigger.
B The ball moves faster.
C The ball changes its direction.
D The ball moves faster in a different direction.

5 Which of the following statements is correct?
A Forces can slow down time.
B Force is neither a push nor a pull.
C Forces can change the mass of an object.
D Forces can change the direction of an object.

6 Which of the following is measured in newtons (N)?
A Size
B Mass
C Energy
D Friction

Force and Pressure 129

7 Ali pushes a 5 N load for 4 m. Salmah pushes a 10 N load for 2 m.
Which of the following statements is true?

A Salmah has done more work than Ali.
B Ali has done more work than Salmah.
C Both Salmah and Ali did not do any work.
D Both Salmah and Ali have done the same amount of work.

8 While performing a pull-up, Salleh lifts a weight of 600 N from the
ground to a height of 0.5 m. How much work has he done?

A 250 J
B 275 J
C 300 J
D 350 J

9 Nurul did 500 J of work when she pushed a load for 5 m. What is the
force exerted by Nurul?

A 10 N
B 50 N
C 100 N
D 2 500 N

10 What is pressure?
A Pressure is the force per unit area.
B Pressure is the mass per unit area.
C Pressure is the mass per unit volume.
D Pressure is the force per unit volume.

11 A cube with sides of 2 m is placed on the ground. It has a weight of
2 000 N. What is the pressure exerted on the ground by this cube?

A 5 Pa 2 m 2 m
B 50 Pa
C 500 Pa
D 5 000 Pa

2 m

12 Def ine (i) mass and (ii) weight.
13 The work done pulling a large rock for 40 m is 6 000 J. Calculate the

force applied.

130 Force and Pressure

Chapter Energy

7 At a solar power station in Seville, Spain, a field of mirrors
(heliostats) directs sunlight onto a tower to generate steam.
This steam is then used to turn turbines to generate electricity.
The Sun is a source of energy. In various parts of the world,
people also depend on fossil fuels as a source of energy. Can you
name other examples of energy sources?

Firman Allah Subhanahu Wa Ta’ala
Tafsirnya:
“(Dialah Tuhan) yang menjadikan api
(yang boleh didapati) daripada pohon
yang hijau untuk (kegunaan) kamu maka
kamupun menyalakan api daripada
pohon-pohon itu.” (80)

He Who produces for you fire out of
the green tree, when behold you kindle
therewith. (80)

(Surah Yasin: 80)

Let’s Explore

• What is energy?
• What are some ways in which we

use energy?
• What are the different forms of

energy?
• How does energy change from one

form to another?
• How can we conserve energy?

Energy 131

7.1 Sources and Forms
of Energy

You should be able to:
• state that energy is the capacity to do work;
• state joule (J) as the S.I. unit for energy;
• identify common sources of energy (e.g. the Sun and fossil

fuels);
• list some of the energy resources in Brunei Darussalam;
• identify different forms of energy.

Energy is the capacity to do work. The S.I. unit of energy is
joule (J). Energy is needed in many activities.

Examples of energy in everyday life

Energy is used in schools to light up our classrooms.
Vehicles such as cars and buses also need energy to move.
Energy is needed to power appliances such as computers.
We even need energy to run or to play.

Energy is used in cooking. We use energy even when
we are sleeping to keep our
hearts beating!

?

Can you name other
examples of how
energy is used?

A television needs energy to function.

132 Energy

Sources of energy

We can get energy from different sources. The Sun and
fossil fuels are common sources of energy.
The Sun
The Sun is the main source of energy for the world. Most of
the energy that living things use comes directly or indirectly
from the Sun. Let us see how energy from the Sun is used.

Sun

Light energy Heat energy

Plants use light energy from Heat energy from the
the Sun to make food. Most Sun is used to provide
animals depend on plants warmth for living
to get energy for their daily organisms. It is also used
activities. to dry your clothes.

Wood from plants
can be burnt to
provide energy.

When living things die,
they decompose into
substances that may
turn into fossil fuels
over millions of years.
These fossil fuels are
used to generate other
forms of energy.

Energy 133

Fossil fuels
Some examples of fossil fuels are crude oil, natural gas and
coal. Fossil fuels are formed when heat and pressure act on the
remains of dead animals and plants over millions of years. The
diagrams below illustrate the formation of fossil fuels.

Water evaporates

300 million years ago Wind

Plants and animals that died were
buried on the ocean floor.

Heat and Pressure
pressure

Decaying
plants and
animals

Over millions of years, the remains of plants and
animals may turn into crude oil and gas due to
high pressure and heat.

134 Energy Rock

Natural gas
Crude oil

Millions of years later, the crude oil and gas are extracted
to be used as energy sources.

Crude oil
Brunei Darussalam is known for its great reserves of crude oil
and gas. Crude oil is obtained from deep underground. It is then
separated in an oil refi nery into many types of fuel. Nodding
donkeys are used to pump crude oil from underground.

Nodding donkeys can be found in Seria, Brunei Darussalam.

The following fl ow chart shows how crude oil is used.

Crude oil

Kerosene

Diesel fuel Bitumen

Gas

Petrol Heavy oil fuel Lubricating oil

Energy 135

Natural gas
Natural gas is also found under the sea. It is used in homes
and factories to fuel heating. Natural gas is also used as a
fuel in power stations to generate electricity.

In Lumut, Brunei Darussalam, natural gas from
under the sea is loaded into tankers for export.

Coal
Coal is obtained from mining deep underground. It is used
in power stations to produce electricity.

Underground coal mining

Excavators are used to mine coal. Pieces of coal

136 Energy

Forms of energy

There are different forms of energy and they can be used for
various purposes. The chart below summarises the different
forms of energy.

Energy

Potential Kinetic Electrical Heat Light Sound

Chemical Gravitational Elastic
potential potential potential

Different forms of energy

Potential energy
When something has potential energy, it means that it
has the potential to release energy. There are three main
kinds of potential energy.
Chemical potential energy
The energy stored in substances that can be released
through chemical reactions is called chemical potential
energy. Objects such as batteries have chemical potential
energy. Even our bodies contain chemical potential energy.

Some sources of chemical potential energy

Cells Petrol Food

Energy 137

Science Smart Gravitational potential energy
The energy an object has because of its position or
Did you know location is called gravitational potential energy. For
that mass affects example, when an object is at a higher position, it has
the amount of more gravitational potential energy than when it is at a
gravitational potential lower position.
energy an object
has? A heavier This ball has gravitational potential energy because
object has more of its position.
gravitational potential
energy than a lighter Elastic potential energy
object at the same The energy an object has when it is stretched or
height. For example, compressed is called elastic potential energy. A
on a diving board, stretched rubber band is an example of an object that
a man weighing 80 has elastic potential energy.
kg would have more
gravitational potential
energy than a man
weighing 50 kg.

The stretched elastic band has When a spring is compressed,
elastic potential energy. it has elastic potential energy.

138 Energy

Kinetic energy
The energy that an object has due to its movement is called
kinetic energy. The greater the speed of a moving object,
the greater its kinetic energy is.

Both types of transport have kinetic energy because they are moving.

Electrical energy
The energy which makes electrical appliances function is
called electrical energy. It is a useful form of energy that
can be transformed into many other forms of energy.

Lightning is also a form of electrical energy. ?

Can you name some
electrical appliances
that you use in your
home?

Energy 139

Heat energy
Heat energy is used in homes for cooking, heating water
and ironing clothes. In factories, heat energy is required for
many processes such as smelting metals, creating steam to
turn turbines and making chemicals react.

Heat energy is used for Heat energy is used for
grilling satay. ironing.

Light energy
The Sun is an important source of light energy in the day.
Without light, the world would be completely dark and we
would not be able to see the things around us.

?

The moon does not Light emitting diodes Living organisms, such as the
produce light, yet we (LEDs) are increasingly firefly, give out light energy on
can see it at night. used for lighting. their own.
Why do you think
this is so?

140 Energy

Sound energy
Sound energy is the energy that can be heard. It is caused
by vibrations of matter such as the vibrations of guitar
strings, piano strings and car engines. Sound travels from
one place to another because the air particles also vibrate.
Therefore, sound cannot travel through a vacuum.

When a fire breaks out, the fire alarm WB Link Activity 7.1
goes off and alerts everyone.

Quick Check

1. What is energy?
2. State the S.I. unit of energy.
3. Give examples of fossil fuels.
4. State the most common energy sources in

Brunei Darussalam.
5. List the different types of energy and how they

are used in our daily lives.

Energy 141

7.2 Conversion of Energy

You should be able to:
• state that one form of energy can be converted to another;
• identify the energy conversions in everyday applications,

including energy converters.

Energy conversion occurs when one form of energy is
converted into another. Let us take a look at some examples.

Example 1
When we strike a match, the chemical potential energy in the
match head is converted into heat energy and light energy.

? The head of the matchstick contains
chemical potential energy.
Can you describe the
energy conversion Chemical potential energy Light energy + Heat energy
that takes place in
this music-playing Example 2
device? When we switch on a television, we can view images and
hear sounds. Like most electrical appliances, the television
gets warm after some time.

The television converts electrical
energy into other forms of energy.

Electrical energy Light energy + Sound energy + Heat energy

142 Energy

Example 3
When a fan is switched on, its spinning blades provide kinetic energy that moves
the air and create wind. The fan gets hot after some time.

Kinetic energy from the fan blades creates wind.

Electrical energy Kinetic energy + Heat energy
Example 4
An electric bell has a hammer and a gong. When the button is pressed, the circuit
is closed and electricity passes through the circuit. This causes the hammer to hit
the gong. Electrical energy from the battery is converted into kinetic energy and
sound energy.

Electrical energy Kinetic energy + Sound energy
WB Link Activity 7.2

Energy 143

Super Scientist Energy converters

Over the centuries, there have been many devices that
convert energy from one form to another. Some of these
energy converters produce electricity. Let us look at some
examples of energy converters.

Dynamo
A dynamo is an energy converter that converts kinetic
energy into electrical energy. It can be found connected to
the wheels of a bicycle. The movement of the bicycle wheels
spins the magnets in the dynamo which in turn generates
electrical energy.

Kinetic energy Electrical energy Light energy

Michael Faraday Dynamo
(1791–1867) was
the famous scientist A bicycle dynamo
who invented the
dynamo. Electric cells
An electric cell is an energy converter that converts chemical
? potential energy into electrical energy. The electrical energy
is then converted to other forms of energy. Two or more
Can you name some cells connected together are called a battery.
forms of energy
that the chemical Chemical potential energy Electrical energy
potential energy
of a battery can
convert into?

Cells are energy converters.

144 Energy

Natural gas power station
Power stations generate large amounts of electricity that is
needed in homes, schools and offi ces.
In a power station, a series of energy changes takes place
before electricity is produced. Electrical generators are used
to convert kinetic energy to electricity. The following diagram
shows the series of energy changes that takes place in a gas
power station before electricity is produced.

1 2
The steam turns the blade of the turbines.
In the boiler, natural gas is burnt
and heat is produced. This heats the Heat energy Kinetic energy of Kinetic
water in the pipe into steam under of steam the steam energy of
high pressure. turbines

Chemical Heat
potential energy energy of
of natural gas steam

Turbines

Chimney Generator

Natural gas Steam Cooling water
supply Water
Water in
Water out

Pipe Burner Boiler 3

The turbines are connected to
a generator that converts the
kinetic energy of the turbines
into electricity.

Kinetic energy Electrical
of turbines energy

Conversion of energy in a power station

Quick Check

Energy can be changed from one form to another.
Give two examples of energy conversion in your
daily life.

Energy 145

7.3 Conservation of
Energy

You should be able to:
• state that in any energy conversion, energy cannot be

created or destroyed, it can only be changed from one
form to another.

Energy can change from one form to another, but it cannot
be created or destroyed. This is known as conservation
of energy. Let us examine the conservation of energy that
occurs in the diagram below.

Light energy Chemical potential energy Chemical potential energy

Sun Plants make food using When animals and plants die
energy from the Sun. Chemical potential energy

Kinetic energy, Electrical energy, Chemical potential energy
Heat energy, Light energy,
Sound energy

Car Petrol Fossil fuels

Quick Check Light energy from the Sun is absorbed by plants and
is converted into chemical potential energy. Animals
Can energy be depend on plants and meat from other animals for this
destroyed? energy. Over millions of years, the chemical potential
energy from dead plants and animals is stored as fossil
WB Link Activity 7.3 fuels such as crude oil and coal. The fossil fuels are then
146 Energy processed into other usable forms where the chemical
potential energy is converted into kinetic, electrical,
heat, light and sound energy.

7.4 Alternative Sources
of Energy

You should be able to:
• identify renewable and non-renewable sources of energy;
• describe briefl y some alternative sources of energy:

hydroelectricity, geothermal, fuel cells, biomass, solar,
wind, tidal and nuclear energy;
• discuss the importance of saving energy;
• explain how to save energy.

Coal, crude oil and natural gas are common sources of
energy but they will not last forever. They are known as
non-renewable sources of energy. Once non-renewable
sources are depleted, they will not be available for
future needs.
Renewable sources of energy are sources of energy that
can be used repeatedly and will not be used up.

Forms of alternative sources of energy

Some non-renewable sources might not be available for the
next generation. Thus, there is a need to fi nd alternative
sources of generating energy. The chart below summarises
alternative sources of energy.

Alternative
sources of

energy

Renewable Non-renewable
sources sources
Nuclear
Hydroelectrical Fuel Solar Tidal
power station cells

Geothermal Biomass Wind

Alternative sources of energy

Energy 147

Hydroelectrical power station
A wall is built across a river and causes the water to rise
behind it, thus forming a large reservoir. This wall is called
a dam.

Srinagarind hydroelectrical power station in Thailand

The diagram below shows how a hydroelectrical power
station generates electricity. Water is stored behind
the dam. The water level is higher than the position of
the turbines. Water fl owing in from the reservoir turns
the turbines.

3
The turbines are connected
to generators that produce
electricity. The kinetic energy of
the moving water is converted
into electrical energy.

1 Reservoir Dam Powerhouse Power lines
Water from the Intake
reservoir fl ows Generator
through the turbines.
It has gravitational Turbine Outfl ow
potential energy.
2
The turbines
turn rapidly. The
gravitational potential
energy is converted
into kinetic energy.

How a hydroelectrical power station works

148 Energy