Secondary 2 science revision

Secondary 2
Science
Revision
BY RICHARD LEE
Mr Naszry’s guns (Mr Naszry
is my science teacher)
Will Join you in Electrical Systems Will Join you in Interactions
Platelet
RBC WBC

Contents
Systems
▪ Transport Systems in Organisms
▪ Human Digestive System
▪ Human Sexual Reproductive System
▪ Electrical Systems
Interactions
▪ Interactions Through the Application of Forces
▪ Energy and Work Done
▪ Transfer of Sound Energy Through Vibrations
▪ Effects of Heat and its Transmission
▪ Chemical Changes
▪ Interactions within Ecosystems

SYSTEMS
TRANSPORT SYSTEMS IN ORGANISMS

Contents
▪ The Need for a Transport System
▪ Transport System in Plants
▪ Transport System in Humans

The Need for a Transport System
▪ Each cell in an organism needs essential substances such as
nutrients and oxygen. In a multicellular organism such as a plant
or a human, there are billions of cells. Most of these cells lie far
from the source of essential substances. Hence, in order to survive,
a multicellular organism needs an efficient way to obtain those
substances. This need is fulfilled by the transport system in the
multicellular organism.

Transport System in Plants
▪ Plants need nutrients to survive. Nutrients for plants are mostly
mineral salts dissolved in water. The mineral salts are needed for
healthy growth of the plant while water is needed for
photosynthesis and other processes. During photosynthesis, food
is produced to provide energy to the plant. The substances need to
reach every cell in the plant. The plant transport system ensures
that this occurs. It consists of roots and vascular bundles. These
work together efficiently to transport substances.

Absorption of water and mineral salts in roots

Transport tissues in plants
▪ Once water and mineral salts are taken into the stem, they are
transported to the leaves by the xylem. The food made is
transported by tubes called the phloem.

Processes involved in the transport of substances
– Diffusion
▪ Mineral salts are able to move in and out of plant cells through
diffusion. Diffusion is the movement of molecules from a region of
higher concentration to a region of lower concentration. The
following explains diffusion.

– Diffusion
▪ In the plant transport system, it is not only mineral salts that are
transported through diffusion. Another example of diffusion in the
plant transport system is the exchange of gases in a leaf during
photosynthesis.

– Osmosis
▪ Water moves in and out of lant cells through osmosis. Osmosis is a
type of diffusion. However, osmosis is more specific in that it is the
movement of only water molecules across a partially permeable
membrane. The following shows the process of osmosis.

Transport System in Humans
▪ Blood is an essential medium of the human transport system. The
system ensures that nutrients and oxygen are quickly transported
to all parts of the body. Thus, the body can produce the energy it
needs in a short time.

Transport System in Humans
▪ The transport of nutrients and essential substances such as
oxygen, are done through diffusion. For example, blood carries
glucose from the digestive system towards the body cells. The
concentration of glucose is lower in the body cells than in blood.
This difference in concentration allows glucose molecules to move
from blood to body cells. Similarly osmosis occurs in the human
body to regulate the amount of water in the body cells.

Circulatory System
▪ The human transport system is called the circulatory system. It
consists of:
▪ The heart;
▪ Blood vessels – arteries, veins and capillaries
▪ Blood – the transport medium
▪ They work together to transport substances in the body.

How does blood act as a transport medium?
▪ Blood is a red fluid tissue or fluid with cells. Blood consists of the
plasma, red blood cells (RBC), white blood cells (WBC) and
platelets.

▪ Plasma contains mainly water. It is the solvent for many
substances that it carries along in the bloodstream. Hence, these
substances are transported from one part of the body to another in
the bloodstream. Functions of the plasma include:
▪ To transport digested food from the small intestine to other parts of
the body.
▪ To remove carbon dioxide and other waste substances produced in
body cells.
▪ To transport other substances such as hormones.

▪ Red blood cells (RBC) are biconcave in shape, which increases the
surface area of the cells. This allows them to take in or release
oxygen at a quicker rate. Red blood cells transport oxygen from the
lungs to other parts of the body. Hence, the lack of red blood cells
would weaken a person and cause him or her to faint.
Hey that’s
me!

▪ Despite being parts of blood, white blood cells (WBC) and platelets
do not help to transport substances. They have different functions
than red blood cells and plasma. White blood cells fight infections
by directly attacking foreign cells (Phagocytes such as
Macrophages), producing antibodies to attack foreign cells
(Lymphocytes such as B Cells), or kill infected cells (Killer cells
such as Natural Killer Cells), while platelets clot the blood when
there is bleeding. We platelets are
technically not blood
cells. We are cell
fragments that
come off a type of
bone marrow cell.

How the transport system works with other
systems in the body
▪ Blood transports oxygen from the lungs, and glucose, glycerol,
fattiy acids and amino acids from the digestive system to the body
cells. Blood also transports oxygen from the lungs to digestive
system cells. Blood also transports carbon dioxide from body cells
to the lungs.
Blood transports
waste materials to
the kidneys, which
filter it out into
urine, which goes
into the bladder.

How the transport system works with other
systems in the body
▪ During respiration, exchange of gases occurs in the human lungs
by diffusion. The gas exchange involves carbon dioxide and oxygen.
When our body cells respire, they make use of oxygen and produce
carbon dioxide as a waste substance. To continue surviving, our
body cells need to restore the oxygen used and remove the carbon
dioxide produced. This is done with the help of the transport
system. The following illustrates how the respiratory system works
with the transport system:

SYSTEMS
HUMAN DIGESTIVE SYSTEM

Contents
▪ Why is the Digestive System Important?
▪ The Human Digestive System
▪ Digestive Enzymes

Why is the digestive system important?
▪ We need food to:
▪ Provide us with energy for daily activities such as walking;
▪ Produce heat to maintain our body temperature;
▪ Maintain a healthy body;
▪ Grow new cells and tissues;
▪ Repair worn out tissues.

What is in the food we eat?
▪ Food provides us with essential nutrients. These are nutrients that
our body needs to survive. There are three main types of nutrients
in food – carbohydrates, proteins, and fats. They are called
macronutrients.

Why must food be digested?
▪ Our body is made up of cells. Each cell membrane is partially
permeable. The membrane allows only small molecules to pass
through. Nutrients such as starch, proteins and fats are large,
complex molecules. These nutrients cannot pass directly through
the cell membrane. So, they must be broken down into molecules
that are small enough to pass through the cell membranes during
digestion. The molecules are glucose, maltose, and sucrose.
I am made
of cells.
I’m a cell.

The Human Digestive System
▪ The digestive system works to carry out digestion and absorption
of food. The organs of the digestive system connect to form a long
tube called the gut. The gut is about 9m long!
The gut is
longer than
I am tall.

What happens to food in the gut?
▪ The organs that make up the gut are the mouth, oesophagus,
stomach, small intestine, large intestine and anus. Besides the
gut, there are other organs involved in digestion called glands.
These glands are the salivary glands, liver and pancreas. As food
passes through the gut, glands produce special juices. These juices
contain enzymes.
An example of
a digestive
enzyme is
saliva.

Digestion in the small intestine
▪ The small intestine, pancreas and liver produce intestinal juice,
pancreatic juice and bile, respectively. These substances pass into
the small intestine to help digestion. Bile is a fluid produced by the
liver. It does not contain digestive enzymes, but it is able to break
up fats into smaller fat droplets. This process is called
emulsification.
The liver also
contains Kupffer
cells, which eat old
red blood cells and
reuse the iron.

Absorption in the small intestine
▪ After food is broken down in the small intestine, the small food
molecules are absorbed by the body.
Then the food
goes into the
bloodstream
and is carried
around the
body.

How the parts of the digestive system work
together
▪ Digestion involves physical digestion and chemical digestion. In
physical digestion, food is broken down physically into smaller
particles. In chemical digestion, enzymes break down complex
food molecules into simple food molecules. The organs of the
digestive system carry out physical and chemical digestion.
Both physical and
chemical digestion
occurs in my mouth,
stomach and
intestines. Same as
anyone else’s.

What are enzymes?
▪ Enzymes are substances that speed up digestion. Chemical
reactions occur when complex food molecules are broken down
into simple food molecules. Enzymes help to speed up the rate of
such chemical reactions. As a result, digestion occurs faster.
My body has
digestive
enzymes.

Types of digestive ezymes
▪ Detergents containing enzymes are mixtures of a few types of
enzymes. This enables enzyme-containing detergents to remove
more than one type of stain. Digestive enzymes are classified
according to the type of food substances they act on.
They help
digest the food
I eat. I usually
eat proteins
for health.

SYSTEMS
HUMAN SEXUAL REPRODUCTIVE SYSTEM

Contents
▪ Human Sexual Reproductive System
▪ Sexual Reproduction
▪ Premarital Sex and Abortion
▪ Birth Control Methods

Human Sexual Reproductive System
▪ Humans, like all other organisms, must produce new organisms
like themselves for the survival of their own kind. This is called
reproduction. Reproduction is an important life process that
ensures the transfer of genetic information from one generation to
another. In other words, it ensures the continuity of a species.

Human Sexual Reproductive System
▪ Humans reproduce through sexual reproduction. Sexual
reproductions involves a male and female adult. In order to carry
out sexual reproduction, males have the male reproductive system
and females have the female reproductive system. The male and
female reproductive systems are both equally important. A couple
may not be able to have children if any part of the reproductive
system in the man or woman fails to function.
I am a
female.

Sexual Reproduction
▪ Sexual reproduction involves the fusion of the male reproductive
cell with the female reproductive cell. This process of fusion is
called fertilization.

Sexual intercourse
▪ For a woman to get pregnant, she must first have sexual
intercourse with a male adult. During sexual intercourse, the erect
penis is inserted into the vagina. The penis ejaculates semen into
the upper end of the vagina. The sperms will then swim into the
uterus.

Fertilization
▪ When a woman gets pregnant, a new individual is formed in her
womb. For a new individual to be formed, fertilization must occur.
Fertilization is the process where the nucleus of the sperm fuses
with the nucleus of the egg.

Pregnancy
▪ In humans, pregnancy lasts about nine months.

Heredity
▪ A baby will grow up to look like his parents. This is because the
sperm and the egg carry information that determines how the
baby will look. The nucleus of the sperm and egg contain genes.
Genes contain instructions that determine the basic characteristics
of a person. Genes are passed on to the new individual when the
nucleus of the sperm fuses with the nucleus of the egg during
fertilization to form a fertilized egg.
I have some
features of my
mom and some
features of my
dad because of
heredity.

Heredity
▪ The passing down of characteristics from parents to offspring is
known as heredity. Heredity is a process by which characteristics
are passed down genetically from one generation to the next. The
following shows some examples of hereditary characteristics in a
family.

Heredity
▪ The children inherit different combinations of physical
characteristics from their parents. Hence, each child in this family
has his or her own unique looks. When these children become
adults, they will pass their genes down to their own children when
they reproduce. Hence, genes are passed down from one
generation to the next.

Puberty
▪ As a child grows older, his or her body experiences many changes.
Between 10-14 years old, our body starts to stimulate the
production of certain sex hormones. Our body also produces a
higher amount of growth hormones that leads to growth spurts.
Sex hormones cause some changes to our body and our body
functions during this period of time. We call this period of time
puberty. The following shows the changes that occur during
puberty:
I have already
finished my puberty.
I have breasts,
which grew during
puberty.

Menstruation
▪ When a female reaches puberty, she starts mensturating.
Mensturation marks the beginning of the menstrual cycle in
women. A typical menstrual cycle lasts 28 days. The changes that
take place in the menstrual cycle are described below.
I always
menstruate.

Premarital Sex and Abortion
▪ Premarital sex is the act of having sexual intercourse before a
couple is married.

Premarital Sex and Abortion
▪ Even though some couples may think that having sex before
marriage would strengthen their relationship, premarital sex often
creates serious problems like Unwanted pregnancy and Sexually
transmitted infections like HIV AIDS.
Luckily, I don’t
have HIV
AIDS.

Premarital sex and abortion
▪ We should have responsible sexual relationships to avoid
unwanted pregnancies and infections. As we grow up, we will be
exposed to many different ideas and values. We should think
about our own values and feelings to make wise decisions for
ourselves. Only then can we be responsible in our sexual
relationship with our partner in this way, we prevent unnecessary
problems from occurring.

Abortion
▪ Abortion is the termination of a pregnancy. During an abortion, a
doctor surgically removes the embryo or foetus from the uterus.
Abortion is usually carried out within the first 12 weeks of
pregnancy.

Birth Control Means
▪ Couples who are not ready to have a child need to use some form
of birth control. Birth control methods are used to prevent
pregnancies.

Contents
▪ Flow of Electricity
▪ Effects of an Electric Current
▪ Household Electricity

Flow of Electricity – Electric current (I)
▪ For an electrical appliance to work, electricity must flow through it.
The flow of electricity is called an electric current. An electric
current is measured by the amount of electric charge moving per
unit time past any point in the circuit. The SI unit is ampere (A).
One ampere of current means that one unit of charge flows in a
second.
My washing
machine, alarm
clock and mobile
phone are all
electrical
appliances.

Electric current (I)
▪ In a closed electric circuit, current flows from the positive terminal
of a battery to the negative terminal. This is known as the
conventional current. After electrons were discovered, it became
known that electron flow actually takes place from the negative
terminal to the positive terminal. Hence, the direction of
conventional current flow is opposite to the direction of electron
flow.

Electric circuits
▪ An electric current flows through a path that is set up by an electric
circuit.
The energy source provides
energy for electric current to
flow in the circuit.
Wires connect the various
components together. This
provides a complete path
for the current to flow.
The bulb converts electrical
energy into light and heat.
A switch turns the current
on or off.

Electric circuits
▪ When we connect various electrical components together, we form
an electric circuit. In order for a circuit to work, all the components
of the circuit must be connected correctly. We can draw a circuit
diagram to help us see if the electrical components are connected
correctly.

Drawing circuit diagrams
▪ We use the common symbols below when drawing circuit
diagrams.
Component Symbol Component Symbol

Drawing circuit diagrams
▪ An example of a simple circuit diagram is shown below.

Series and Parallel Circuits
▪ There are two types of electric circuits – series circuit and parallel
circuit.

Measuring current
▪ We measure current using an ammeter. The terminals of an
ammeter are marked with + and - signs.

Potential difference (V)
▪ Electric charges need energy to push them along a circuit. Water
always flows from higher to lower ground. Similarly, a positive
electric charge always flows from a point of higher potential to a
point of lower potential. An electric current can flow only when
there is a potential difference (V) or p.d. The potential difference
between any two points is the amount of energy needed to move
one unit of electric charge from one point to the other.

Potential difference (V)
▪ The SI unit of potential difference is the volt (V). One volt of
potential differences means that one joule of energy is needed to
move one unit of charge. The more energy needed to move charge
between two points in a circuit, the greater the potential difference
between the two points.l

Measuring potential difference
▪ We measure potential difference using a voltmeter. The teminals
of a voltmeter are also marked with + and - signs. Since a
voltmeter measures the p.d. of a component, the voltmeter must
be connected in parallel to the circuit component.

Resistance (R)
▪ An electrical component resists or hinders the flow of electric
charges when it is connecter in a circuit. In a circuit component,
the resistance to the flow of charge is similar to how a narrow
channel resists the flow of water.

OPTIONAL FOR NA: How the arrangement of
circuit components affects resistance
▪ If a circuit contains only fixed resistors, we can adjust the
resistance of the circuit by connecting fixed resistors in different
arrangements. When connected in series, the light becomes
dimmer. When connected in parallel, the light becomes brighter.
Normal
Academic
must know!

OPTIONAL FOR NA: Variable resistors (rheostats)
▪ We can adjust the resistance in a circuit over a range of values.
One way to do this is to use a variable resistor or rheostat. A
rheostat is a resistor whose resistance can be adjusted easily.
Rheostats are used to adjust the sound volume of radios and the
brightness of light bulbs.
Normal
Academic
must know!

Effects of an electric current.
▪ A mobile phone makes use of an electric current to produce light.
At the same time, the sound produced by the phone depends on
the magnetic effect of an electric current. We rely on the effects of
electric currents every day. These effects are:
▪ Chemical effect;
▪ Heating effect;
▪ Magnetic effect;
▪ Lighting effect;
My mobile
phone is an
old one.

Chemical effect of an electric current
▪ When an electric current is passed through certain liquids, a
chemical change can be observed. This chemical effect is made
use of in electrolysis and extraction of metals.

Extraction of metals
▪ Electricity can be used to break down compounds into its
elements. This process is called electrolysis

Electroplating
▪ Many objects around uis, such as the audio jack connector are
coated with a metal by immersing the object in a liquid and then
passing an electric current through the liquid. This method of
coating metals on objects is called electroplating.

Magnetic effect of an electric current
▪ An electric current has an effect on magnets. We can see this
effect when an electric current flows near a compass.

▪ The magnetic effect can be increased by making current flow in a
coil of wire called a solenoid. This has many useful applications.

▪ Electromagnets are used in the motors of electric fans and DVD
drives. A strong magnet in the motor in each appliance interacts
with the electromagnet. This causes the blades to rotate.

Telephones
▪ In telephones, a changing magnetic effect causes a thin sheet of
metal to vibrate. The diaphragm is made of a metal that can be
attracted to magnets.

Heating effect of an electric current
▪ When an electric current passes through a wire, the electrical
energy is converted to heat. In heating appliances, the heating
element is made of materials with high melting points. An
example of such material is nichrome.

Heating effect of an electric current
▪ The heating effect of a current can lead to the lighting effect.

Household Electricity
▪ We use electrical energy at home everyday. The amount of energy
we use depends on the appliances we use and the duration they
are switched on for.
I keep using
electronic
appliances
everyday.

Power
▪ An electric fan is an example of a household appliance that we use
everyday. An electric fan that blows strongly can be said to be
powerful because it converts electrical energy quickly into the
energy of moving air.

Power
▪ The SI unit of power is the watt (W). One watt of power means that
in one second, one joule of electrical energy is converted to other
forms of energy. Some household appliances convert electrical
energy more quickly than others. The power rating of an appliance
tells us how quickly an appliance converts electrical energy into
other forms of energy. The power rating is usually printed on a
label at the back or under the appliance.
My car produces
515 000W of
power. This is
equivalent to
690
horsepower.

Power
▪ Most household appliances use a large amount of energy in one
second. Hence, their electrical power is usually measured in
kilowatts instead of watts.

Electrical energy usage in a home
▪ We can measure the amount of electrical energy using the
formula Energy = Power x Time where power is measured in
kilowatt, and time is measured in hours. If an appliance has a
power rating of 1 Kw, and is used for 1h, then the electrical energy
converted by the appliance is 1 kWh. This amount of energy is
called the kilowatt hour (kWh). This is the most common unit we
use to calculate the cost of using electrical energy at home.
Normal
Academic
must know!

Hazards of electricity
▪ Electrical appliances safely convert electrical energy into useful
energy only if they are not damaged. If we used damaged
appliances, hazards such as electrical fires and electrocution may
occur.

Electrical fires
▪ Electrical appliances such as electric irons and kettles require
large currents to produce heat. The wires in most electrical
systems do not heat up because the components in the circuits
resist the flow of electric charge. This ensures that the current is
not large. Large currents can occur when electrical currents are
damaged, do not work properly, or misused. For example, if too
many plugs are inserted into the same power socket, this may
draw a large current. The large current generates heat, which may
melt the insulation and even cause a fire.

Electric shocks and electrocution
▪ Besides the danger of fire, large currents are dangerous when they
pass through a person’s body. When this happens, he or she will
experience an electric shock or electrocution. This usually results
in serious injury or death. This can happen in appliances with
metal casing or metallic parts on the outside.
I got an
electric shock
once when I
accidentally
touched a live
wire with my
wet hands.

Electric shocks and electrocution
▪ A large current can pass through our body even if we do not
directly touch a wire at a high electric potential. This can happen if
we do not switch off electrical appliances and pull out the plug
when cleaning them. We may accidentally touch the exposed
metallic parts that conduct electricity. To prevent electrocution, the
following precautions should be taken:

Safety features in the household electrical system
▪ The flow of a large current in wires or in our body is an electrical
hazard. To deal with large currents, three safety features are found
in all household circuits:
▪ Earth wire;
▪ Fuse;
▪ Circuit breaker.

Earth wire
▪ Three types of electrical wires are found in the household: The live
wire, the neutral wire, and the earth wire.

Fuse
▪ The fuse makes use of the heating effect of an electric current to
switch off a large current. A large current causes a short, thin wire
in the fuse to heat up and melt. A fuse is connected to the live wire
and is rated with the current that will melt the wire in it. When the
wire in a fuse melts, we say the fuse has blown. A blown fuse
should be replaced after an electrical fault has been rectified.

Circuit breakers
▪ Instead of a fuse, a device called a circuit breaker can also cut off
electric current. Unlike a fuse, a circuit breaker does not need to
be replaced. The circuit breaker in our home is found in a box
called the consumer unit. Each circuit breaker is a switch-like lever
connected to a different part of the household circuit. After fixing a
damaged appliance or damaged part of the circuit, the circuit can
be switched on again using the circuit breaker.

INTERACTIONS
INTERACTIONS THROUGH THE APPLICATION OF FORCES

Contents
▪ Types of Forces
▪ Measuring Force
▪ Effects of Forces
▪ What is Pressure?

Types of Forces
▪ A force may be described as a push or a pull. We interact with
forces whenever we grip the poles or hold hand straps in a bus. We
usually apply forces on an object by touching it with our body, or by
touching it with another object. However, forces can also act when
objects do not touch. In general, there are two types of forces:
contact forces and non-contact forces.

Contact forces
▪ Whenever an object is touched, contact forces act on it. For
example, the tires of a car rest on the road and exert a contact
force on the road. The contact force that acts on two materials
rubbing against each other is called friction.
When the car moves, however, another
contact force is applied on the road.
The rough rubber tires rub against the road
surface. Friction enables the tire to push
backwards against the road. This causes the
wheel to turn and the car to move forward.
My car is a
Lamborghini. I
nearly crashed
it while driving
at 200 mph.

Non-contact forces
▪ A force that acts on an object without touching it is called a non-
contact force. Gravitational force, electrostatic force and magnetic
force are three examples of non-contact forces.

Gravitational force
▪ Gravitational force is the force that attracts objects to planets. This
force affects the earth, the moon, and the planets in the Solar
system. We see the effects of this attractive force all around us.
Gravitational
force is
acting on me
right now.

Ocean tides
▪ We see the effect of gravitational force in the movement of high
and low tides in harbors, ports, and coastal areas. The tides on the
earth are caused partly by the moon’s gravity pulling on the waters
of the oceans.

Weight
▪ The force of gravity pulls paperweights down on loose sheets of
paper, preventing the paper from being blown away by wind. The
force of gravity also keeps us seated in our chairs.
Mass and weight
are two entirely
different things.
You will learn
about that later.

Electrostatic force
▪ We can feel electrostatic forces when we use a transparent sheet
of plastic to wrap a book. The hair on our arms and the dust on the
table are attracted to the plastic wrap because of electrostatic
forces. An electric charge can be positive (+) or negative (-).
You should
have learnt
electric
charge in
chapter 13.

Magnetic force
▪ Magnetic force, or magnetism, is the force exerted by a magnet on
magnetic materials such as iron and steel. Every magnet has a
north pole and south pole.

Measuring Force
▪ In everyday language, the weight of a person is measured in
kilograms. However, weight is in fact the force that the earth
exerts on objects. Therefore, weight should be measured as a
force. The SI unit of force is the newton.

Instruments for measuring force
▪ The spring balance is an instrument that is used to measure force.
There are two types of spring balance: the extension spring
balance and the compression spring balance. In both types, a
pointer attached to the spring indicates the amount of force acting
on the spring.

Mass and weight
▪ The force of gravity (weight) is different on different massive
objects like planets. The weight of a person is greater than his
weight on the moon. This is due to stronger gravity on earth.

Effects of Forces
▪ Although we cannot see forces, we can see their effects on
objects. Below are some examples on how we make use of forces
to help us do things.

Effects of forces on the size or shape of an object
▪ When we apply a force on an object, its physical dimensions may
change, like in this plasticine.

Effects of forces on the motion of an object
▪ During a hockey game, each player uses his/her stick to apply
forces on the ball. These forces affect the motion of the ball.

Speed
▪ We learnt that forces can cause an object to move faster or move
slower. In short, forces can change the speed of a moving object.
Speed is the distanced travelled per unit time. Speed can be
calculated using the formula: Speed= Distance travelled/Time
taken.
My car has a top
speed of 230
mph or 370
km/h. That’s
370 kilometers
in 1 hour!

Turning effect of forces on an object
▪ When we open the door, we apply a force on the door knob or
handle.

Levers
▪ Levers are tools that help us do things more easily. By applying a
force to one point of a lever, we overcome the turning effect of a
nother force.

Pressure
▪ Pressure is an effect of a force acting on an object. The amount of
pressure exerted depends on the amount of force and the area on
which the force acts. In our everyday life, we encounter pressure
exerted by many other objects and substances.

Factors affecting pressure
▪ If we measure the amount of force applied on a surface and the
area of the surface, we can calculate the pressure. Pressure is the
amount of force acting perpendicularly on a unit area. Pressure is
related to force and area by the formula Pressure=Force/Area
Normal
Academic
must know!

Pressure in everyday life
▪ The effects of pressure can be advantageous or disadvantageous
to us in our everyday life.

Atmospheric pressure
▪ The air around us exerts pressure on all objects that are exposed
to air. The pressure exerted by the air in the earth’s atmosphere is
called atmospheric pressure. Wed o many things that rely on
atmospheric pressure. Like for example, when we drink liquid
using a straw, we make use of atmospheric pressure to push water
up the tube.
Normal
Academic
must know!

Atmospheric pressure
▪ We make use of atmospheric pressure to hold suction hooks
securely on kitchen and bathroom tiles, and car windscreens.
Normal
Academic
must know!
My car has a
suction cup with
a phone holder.

Pressure in liquids
▪ When and object is immersed in a liquid, the liquid exerts the
pressure on it. The deeper the object is immersed, the greater the
liquid pressure.
Normal
Academic
must know!
Don Walsh and
Jacques Piccard
experienced
water pressure
in the trench.

Submarines
▪ Submarines dive to great depths underwater. The rigid metal body
of a submarine is built to withstand the very high pressure deep
underwater. If the submarine dives beyond a certain depth, the
pressure may become too high and damage the submarine.
Normal
Academic
must know!
My country’s
navy’s new
submarine is
powered by
lithium-ion
batteries.

Water supply
▪ In most high-rise buildings in Singapore, water is delivered to and
stored in a tank at the top of the building. This causes water in the
pipes below the tank to be at a high pressure. The high pressure
ensures that water flows to the units below.
Normal
Academic
must know!
I don’t live in
Singapore. I live in
Japan. I live in a
traditional
Japanese house
with a pond and
tatami mats.

INTERACTIONS
ENERGY AND WORK DONE

Contents
▪ Energy and Work Done
▪ Energy Changes
▪ Sources of Energy

Energy and Work Done
▪ When we take the elevator or ride an escalator, a motor uses
electrical energy to do work. By moving our bodies up to a higher
floor, elevators and escalators convert electrical energy into useful
work. Without energy, machines and people are not able to do
work.

Energy and Work Done
▪ Energy is the ability to do work. The SI unit for energy and work
done is the joule (J). One joule of energy is needed to do one joule
of work. In order for work to be done on an object, two conditions
must be met:
▪ A force acts on an object;
▪ The object moves in the same direction as the force.
▪ If any of these two conditions is not met, no work is done. Work is
not always done when a force is applied.

Energy Changes
▪ When work is done on an object, energy is converted from one
form to another.

Energy Changes
▪ When work is done, we have seen that each form of energy
present was converted from another form of energy. This is
because energy cannot be created or destroyed. We say that
energy is conserved.

Energy Changes
▪ The energy of the swing continuously changes between kinetic and
potential energy. However, the total amount of energy remains
constant at all points during the swinging. The gravitational
potential energy lost is converted into kinetic energy. Energy can
be converted from one form to another, but it cannot be created or
destroyed. Hence, the swing continues to move to and from. This
motion will go on forever, assuming that no other conversion of the
energy takes place.

Sources of Energy
▪ Although energy cannot be created or destroyed, energy is not
always converted into useful forms. Many machines pollute the
environment and waste energy. Riding a bicycle wastes much less
energy than driving a car. Furthermore, the energy we use during
cycling is the same energy we use in walking.
I should stop
driving my car.

Sources of Energy
▪ We get energy from many sources. There are generally two types
of energy sources: renewable and non-renewable.

Non-renewable sources of energy
▪ Much of the energy we use such as in cars and motorcycles comes
from non-renewable sources. These sources of energy are limited
and will run out one day.
I use non-
renewable
energy.

Fossil fuels
▪ Most non-renewable sources of energy are produced from fossil
fuels. Fossil fuels are formed by the remains of dead plants and
animals. It takes millions of years for fossil fuels to form.
My car burns
oil, a type of
fossil fuel.

Fossil fuels
▪ An important type of fossil fuel is crude oil, which is a black liquid.
Other types of fossil fuels include natural gas and coal. In power
stations, the burning of fossil fuels involves an energy conversion
from Chemical Energy to heat energy to kinetic energy to electrical
energy.
In motor vehicles such as
cars and motorcycles like my
car, the energy conversion is
from chemical energy to
heat energy to kinetic
energy.

Uses of fossil fuels
▪ Petrol is a fuel for cars and motorcycles, while diesel is a fuel for
buses, taxis (although most taxis use petrol) and trucks. Kerosene
is a fuel for jets and also is stored as fuel for cooking along with
natural gas. Most power stations generate electrical energy by
burning coal or natural gas.
My current truck
uses petrol, unlike
my previous truck,
which uses diesel.
My car
originally, runs
on petrol, but I
added a hybrid
system to it.

Impact of the use of fossil fuels on the
environment
▪ When fossil fuels are burnt, the carbon dioxide gas produced traps
heat from the sun in the earth’s atmosphere. The heating up of the
atmosphere is causing the ice in the North and South poles to
melt, raising sea levels. Global warming also causes more
unpredictable and destructive weather patterns.
I should cut the
use of certain
things.

Renewable sources of energy
▪ Some sources of energy can be sustained or renewed indefinitely.
These sources are called renewable sources of energy. Unlimited
supplies or new growth of organisms allow us to use these sources
of energy continuously. Biofuels, geothermal energy, hydroelectric
energy, solar energy and wind energy are examples of renewable
sources of energy.

Biofuels
▪ Biofuels are fuels derived from animal and plant matter such as
water hyacinth and sugar cane. Biofuels, like fossil fuels, are burnt
to produce energy. Hence, the energy conversion for biofuels as an
energy source is the same as that for fossil fuels.

Uses of biofuels
▪ Ethanol derived from sugarcane and water hyacinth can be turned
into biodiesel.

Impact of the use of biofuels on the environment
▪ Carbon dioxide is produced when biofuels are burnt, contributing
to the heat trapped in the earth’s atmosphere. However, the plants
that produce these biofuels take in carbon dioxide during
photosynthesis. If these plants are grown as quickly as they are
burnt, it will partially offset the contribution of trapping heat in the
atmosphere.

Geothermal energy
▪ Geothermal energy is energy derived from hot rocks deep
underground in volcanic areas. By drilling deep into the earth,
water flowing through huge underground pipes is heated into
steam.

Uses of geothermal energy
▪ The steam from heated water in geothermal power stations can be
used to heat homes and buildings or generate electricity.

Impact of the use of geothermal energy on the
environment
▪ Some types of geothermal power stations extract poisonous
substances such as hydrogen sulfide or arsenic from deep
underground. Because material from underground is extracted, the
land around these geothermal power stations may sink, causing
damage to buildings and roads. The flow patterns of rainwater may
also be significantly affected.

Hydroelectric energy
▪ Hydroelectric power stations store water in a reservoir behind a
dam. The flow of water from the reservoir turns the blades of a
turbine to generate electrical energy.

Uses of Hydroelectric energy
▪ Hydroelectric power stations supply electrical energy to
households and factories.

Impact of the use of hydroelectric energy on the
environment
▪ Hydroelectric power stations do not produce pollutants. However,
during the construction of hydroelectric dams, the damming of the
river can cause extensive flooding in large areas of forest, wildlife
habitats and farmland. The dams also prevent the flow of
sediments and nutrients down rivers. The ecosystems around
hydroelectric power stations are therefore greatly affected.

Solar energy
▪ The energy in sunlight can be directly converted into electrical
energy by photovoltaic or solar cells.
I am too shy to
answer this.
Anyways, my car
has solar panels.

Uses of solar energy
▪ The energy in sunlight can be used to heat water. Some solar
heaters can channel the heated water (steam) to drive a turbine to
generate electrical energy. However solar PV cells can directly
convert sunlight in to electrical energy.
On hot summer days,
the solar panels on my
car provide energy to
the air conditioning
system to keep it nice
and cool.

Impacts of the use of solar energy on the
environment
▪ No harmful substances or pollutants are produced when solar cells
generate electricity.
Solar energy is
environmentally
friendly!

Wind energy
▪ Wind energy is an energy source that converts the energy of
moving air into electricity by rotating one or more turbines.
Back in my home
country, there are
wind turbines. This
here is a picture of
wind turbines in my
home country.

Uses of wind energy
▪ Wind energy provides electrical energy for households and
research stations, especially in remote areas.
Wind turbines are
surely very
powerful machines.

Impact of the use of wind energy on the
environment
▪ The wind blades of turbines may cause a significant number of
deaths of birds and bats. The rotating wind turbines produce some
low-frequency noise, including infrasound. Some people may feel
nauseous and experience headaches if they are exposed to
infrasound for long periods of time.
Oh my! If my pet
bird were there,
will she be killed?

INTERACTIONS
TRANSFER OF SOUND ENERGY THROUGH VIBRATIONS

Contents
▪ What Causes Sound?
▪ How We Hear Sound
▪ How Does Sound Vary?
▪ Sound and Society

What causes Sound?
▪ Sound is all around us. The movement of objects create sound.
Sound must travel through a medium like gas liquid or solid. The
ringing of a bell goes silent if air is absent. This is because the
vibrations of the ringing bell are not passed onto surrounding
molecules.

How sound travels
▪ Sound is caused by vibrations of matter. The vibration of the
speaker diaphragm causes the air molecules next to it to also
move from side to side in a regular pattern. This helps to carry the
sound energy away in a moving pattern. Sound produced is shown
as ripples moving away from the source. Each ripple shows where
the molecules are bunched up.

How sound travels in different media
▪ Sound travels at different speeds in different media.

Speed of sound in a solid
▪ We are disturbed by the sound of drilling in neighboring houses.
When molecules at one end start to vibrate, energy is transferred
from the neighboring molecules very rapidly. This is because the
molecules are packed very closely together. Hence, the speed of
sound is the fastest in solids from 5000 to 6000 m/s.
I sometimes
hear drilling
noises.

Speed of sound in a liquid
▪ Scuba divers sometimes draw the attention of others by tapping a
metal pointer on their metallic air tanks. When molecules at one
end start to vibrate, energy is transferred to the neighboring
molecules less rapidly. This is because the molecules of a liquid
are not packed as closely together as those of a solid. Hence, the
speed of sound is slower in liquids at 1500m/s.
I never scuba
dive.

Speed of sound in a gas
▪ We hear public announcements through megaphones of PA
systems. When molecules at one end start to vibrate, energy is
transferred to the neighboring molecules slowly. This occurs within
a gas as the molecules are far apart from one another. Hence the
speed of sound is the slowest in gases at 330 m/s.
In Japan, my
country, these
PA
megaphones
play a tune at
5 PM every
day.

How We Hear Sound
▪ Communication is important in our daily lives. It requires hearing
the sounds made by others during conversations. Technology such
as hearing aids can be used to improve our sense of hearing. This
helps people with hearing loss – such as the deaf – communicate
with others.

How We Hear Sound
▪ Sound occurs when a vibrating object disrupts the air around it.
The vibrating air molecules, in turn, cause structures within the
ears to vibrate. The vibrations pass the sound energy to our earws.
The brain translates the vibrations into information. For the deaf, a
hearing aid increases the loudness of sounds by producing greater
vibrations of air molecules.
I am not deaf
as my ears are
working very
well.

How Does Sound Vary?
▪ We can identify sounds according to how they differ. Sounds can
differ in pitch and loudness.

Pitch
▪ We hear and produce sounds of different pitch. When you sing the
tune do-re-mi, you are singing notes of increasing pitch.
My euphonium
can play in the
middle.
Normal
Academic
must know!
My voice is
high pitched,
but I have a
tuba at home.
It produces a
low pitch.

Sounds of different pitch
▪ Here are some examples of pitch:
▪ Examples of sounds of low pitch are a cow mooing and the sounds
made by a bass guitar or a large drum.
▪ Examples of sounds of high pitch are ta dentist’s drill at high speed
and the squeaking of a mouse.
▪ Larger musical instruments like the tuba generally produce sounds of
lower pitch.
▪ Smaller musical instruments like the trumpet produce sounds of
higher pitch.
I have a
tuba. I call
it Tuba-
cabra.
I have a
trumpet.

Frequency of sound
▪ When a musical instrument produces sounds at the wrong pitch, it
needs to be tuned. A tuning fork can help a musician check that an
instrument produces sounds of the correct pitch. A tuning fork will
produce a pure note that has only one pitch. Different tuning forks
produce different musical notes.
I tune my
euphonium to
make sure my
euphonium is
the correct
pitch.

Frequency fo sound
▪ The number of cycles per second made by the vibrating source of
sound is called the frequency of the sound. The higher the
frequency, the higher the pitch. The unit of frequency is one hertz
(Hz). One hertz is one cycle per second. We can hear and detect
sound ranging from 20 Hz to 20,000 Hz. However, this range may
vary slightly with each individual.
My
euphonium’s
musical range
is around 82
Hz and 311 Hz.

Loudness
▪ By moving its ears, a rabbit can make the sound it hears louder.
However, the source itself can also produce louder sounds. The
loudness of sound depends on how big the vibrations in the
medium are. Greater vibrations with greater energy produce louder
sounds. For example, beating a drum harder produces larger
vibrations that create louder sounds.
My
trumpet is
very loud.

Sound and Society
▪ Humans and animals alike use sound as a main means of
communication. Without sound, we will be isolated from one
another and the world around us.
This is more
evident in the
deaf, they
would be
isolated from
one another
and the world
around us.

Uses of sound
▪ We rely on sounds for a variety of reasons.
▪ Warning of danger
▪ Entertainment
▪ Communication
Sometimes, I
get annoyed
by sound.

Warning of danger
▪ Sound can be used as an alarm. We shout to warn or alert others
of a disaster. Loud sirens warn people of approaching danger (e.g.
air raid) or alert people to give way to an emergency vehicle (e.g.
ambulance). Animals growl to warn others to avoid them or as a
signal before attacking.
An example of an
emergency vehicle is
an ambulance. I
sometimes ride in
ambulances. I usually
spend time in the
hospital because I’m a
nurse, of course.

Entertainment
▪ Sound can also be used for our listening pleasure. These sounds
are pleasant to our ears. People may pay to enjoy the sounds that
please them. For example, some people invest in a sound system
to listen to music at home.
My favorite
song is Bruno
Mars: Count on
Me.

Communication
▪ We talk in order to communicate with one another. Even animals
make distinct sounds to communicate danger, give
encouragement or alert others to available food.
I always talk
to my friends.
I vow not to
keep a wolf as
a pet.

Sonar
▪ Reflected sounds (echoes) from the ocean floor can provide
information about underwater conditions as well as objects
surrounding the ship. Ships use sonar to detect shoals of fish and
large whales. Sonar is a technique that uses sound to gather
information about the environment.
Submarines
also use a
sonar, but
underwater.

Ultrasound and technology
▪ Ultrasound is used in hospitals to observe the internal body
without the need for an operation. It is defined as sound with
frequencies above 20000 Hz, which cannot be heard by the
human ear. For example, ultrasound allows doctors to observe
fetuses in pregnant mothers, detect cancers and observe tumors
within the body. It is also used to monitor blood flow in the veins
and abnormalities within the heart. Doctors also use ultrasound to
break up kidney stones into small pieces so that they can be
passed out of the body easily, thus avoiding surgical operation.
I have gone
through
ultrasound
scanning
before.

Noise
▪ While sounds such as music may be pleasing to our ears, some
sounds are unpleasant to our ears. Noise is a collection of notes
that is unpleasant and may be even harmful. While we love the
sound of music, we feel differently about noise. Examples of noise
are chalk scratching the blackboard, dishes breaking and cats
yowling loudly at night.
I am allergic to cats.
But, I am always careful
when handling dishes.

Range of noise pollution
▪ Noise pollution is excessive noise that may come from humans,
animals or machines. It may cause annoyance as well as health
problems. The loudness of sound is measured in decibels (dB).
Sounds should be kept within acceptable limits as high sound
levels can have negative health consequences. For example,
extremely loud sounds can lead to hearing impairment due to
burst eardrums.
Soundwaves
become
shockwaves
My trumpet
can reach a
loudness of
110-120dB.

INTERACTIONS
EFFECTS OF HEAT AND ITS TRANSMISSION

Contents
▪ Expansion and Contraction of Matter
▪ Effects of Expansion and Contraction
▪ Movement of Heat

Expansion and Contraction of Matter
▪ The degree of hotness or coldness of an object is measured by the
object’s temperature. A common unit for temperature is the
degree Celsius. The SI unit for temperature is the Kelvin. When
heat is applied to a substance, it increases in volume. We say the
substance expands. We call this process expansion. When a
substance is cooled, contraction occurs and the substance
contracts.
37 degrees
Celsius is also
equal to 310
Kelvin.

Expansion and contraction in solids
▪ When we pour boiling water too quickly in a cup made of thick
glass, the glass sometimes cracks. The solid glass on the inside
expands more quickly than the outside when heated. For this
reason, the walls of the glass containers for hot liquids are usually
thin.
I am not going
to pour hot
water quickly
in my glass
drink again.

Expansion and contraction in liquids
▪ In mercury thermometers, the liquid mercury responds quickly to
heat. The mercury level changes when the liquid is heated or
cooled. This occurs when the volume of the mercury changes.
When I’m sick,
I use a
thermometer
to check my
temperature.

Expansion and contraction in gases
▪ When we bake a loaf of bread, the bread dough rises. This is partly
because the air bubbles trapped in the dough expand when
heated.
I like to eat
bread.

Effects of Expansion and Contraction
▪ When a body expands or contracts, large forces may be set up.
This can either help or hinder us.

Many things
expand and
contract. If
telephone
wires break, I
cannot call.

Movement of Heat
▪ Heat is an important part of our life. If we fail to consider the
effects of heat, disasters can occur. We can make our lives easer
and safer by considering the movement of heat in different
objects. Heat flows from a region of higher temperature to a region
of lower temperature. For example, when stirring a hot drink, the
spoon used to stir the drink becomes warm. If the drink is left to
stand on the table for some time, the drink eventually cools.
I always stir
coffee before
drinking it.

Movement of Heat
▪ The movement of heat occurs through one or more of the following
processes:
▪ Conduction
▪ Convection
▪ Radiation

Conduction
▪ Conduction is the process of heat transfer through a medium or
material without any movement of the medium or material. Such
material is called a conductor. Bad conductors are called
insulators. At room temperature, certain objects feel warmer to
the touch than others. This is because some objects are better
conductors of heat than others.
Looks like my
euphonium is a
heat conductor
because it is
made of brass,
which conducts
heat.

Good and bad conductors of heat
▪ Most metals are good conductors of heat. However, some metals
conduct heat better than others. However, materials such as wood,
rubber, asbestos, plastic, glass, water and air are bad conductors
of heat. They are used to reduce the amount of heat from being
transmitted from one place to another. Most liquids are bad
conductors of heat, except for mercury.
When I touch
my euphonium,
it is cold
because it is a
good heat
conductor.

Uses of heat conductors
▪ Good conductors are used whenever heat has to be quickly
transferred from one place to another. Good conductors are found
in items such as cooking utensils, radiators, miners’ lamps, and
boilers.
I have a
radiator in my
house because I
live in a cold
temperate
climate, which
gets very cold
in winter.

Uses of heat insulators
▪ Bad conductors are used to reduce the amount of heat transfer.
They are found in walls of buildings and in items such as the
handles of cooking utensils.

Convection
▪ Convection is the transfer of heat from one place to another
through the movement of fluids. A fluid of lower density rises in a
fluid of higher density. A fluid will sink when its in a fluid of lower
density. Convection takes place due to the expansion of a fluid.
When a fluid is hot, its volume increases. This means its density
decreases. The less dense fluid then rises while the denser fluid
flows in to take its place.

Convection in liquids
▪ When a pot of water is heated, the hot, less dense water at the
bottom rises to the top. This is replaced by cold denser water from
the top moving down. Heat is carried from one place to another by
the movement of the water itself.
I always boil
water when
making Milo.

Convection in gases
▪ Convection also occurs in gases. For example, in the past, coal
mines were ventilated by vertical shafts sunk into the mines.
These were joined by horizontal passages. A fire is lit at the bottom
of one shaft. This causes hot, less dense air to rise from the shaft
and cold, denser air to enter the other shafts.
Those coal
mines were
where many
power plants
got their coal
from.

Applications of convection
▪ Household Ventilation
▪ This is used to cool a house. Because of its lower density than cool air,
hot air rises and collects under the ceiling. A cool room has features
that let hot air out and cool air in. For Example, a high ceiling with air
vents allows hot air to rise and escape, while doors and windows allow
cool air to enter. In modern homes, the ceilings do not have air vents.
Instead, they use air conditioning to keep the room cool.
My house does
not use air
conditioning.
This is to save
the world.

▪ Electric kettle
▪ Convection currents play an important part in heating water quickly in
an electric kettle.
I don’t use an electric
kettle, but I use a
regular kettle. You
know that scene from
Thomas and the Magic
Railroad? Diesel 10
exclaimed “TIN
KETTLE!!!” when he
fell off the bridge!!!
It is so funny!!!

▪ Car radiator
▪ A car radiator gets rid of heat mainly by conduction and convection.
My car has a
powerful
radiator to
make sure the
engine is
cooled when
travelling very
fast.

▪ Land and sea breezes
▪ Land and sea breezes are caused by convection.
I’m not going
to the sea.

Radiation
▪ Radiation, the transfer of heat in the form of waves from one place
to another without a medium for transmission, is a method of heat
transfer that does not require the presence of matter. This means
that heat can radiate across empty space or a vacuum. For
example, heat from the sun radiates across millions of kilometers
of empty space to reach earth.
I’m not
exposing
myself to the
sun for long
periods of
time because I
might get skin
cancer.

How a body radiates heat
▪ Not all objects radiate or absorb heat at the same rate. It depends
on:
▪ The nature of the surface of the body,
▪ Total surface area of the body,
▪ Temperature of the body.
Even humans,
like me,
radiate heat.

Uses of good and bad radiators of heat
▪ Good and bad radiators of heat can depend on the color of the
object. When it’s white, it’s a bad radiator of heat. When it’s black,
it’s a good radiator of heat.
I usually wear
these clothes.
When doing
presentation, I
wear my school
uniform. Problem
is, most of my
usual clothes is
black, which
absorbs heat.

Applications of heat transfer
▪ There are many applications of heat transfer around us. In each
application, all three processes of heat transfer – conduction,
convection and radiation – are involved.

Design of spacesuits
▪ Living conditions in space are very harsh. Not only is there no air
for humans to breathe, but temperatures can be very high in some
places and very low in others. Astronauts on space shuttle
missions usually have to work outside their shuttle. Thus, it is not
important that the astronauts’ spacesuits are able to keep the
temperature at a comfortable level.
I’m not going
to space.

Vacuum flasks
▪ A hot liquid in a vacuum flask stays hot because the vacuum flask
is designed to reduce heat loss from the liquid by conduction,
convection and radiation. The different parts of the flask work
together to keep a liquid hot. It is also effective in preventing heat
from entering the flask. A cold liquid in a vacuum flask stays cold
for the same reasons that a hot liquid stays hot.
I use vacuum
flasks because
the weather in
my country is
cold.

Keeping buildings cool
▪ In hot countries, the buildings are designed to keep the people
comfortable and cool.
The hottest
temperature
my country,
Japan,
experienced
was 41.1°C in
Shizuoka
Prefecture.

Contents
▪ Chemical Changes as a Result of Interactions
▪ Types of Chemical Changes
▪ Types of Chemical Changes – Interactions between Matter
▪ Movement of Atoms during Chemical Reactions
▪ Effects of Chemical Changes – Friends or Foes?

Chemical Changes as a Result of Interactions
▪ Changes take place around us all the time. Changes can be
classified as physical changes or chemical changes. Example of
physical changes are dissolving of sugar or salts in water and
evaporation. Physical changes are reversible. They do not involve
the formation of new substances.
Another physical
change that
happens is when I
accidentally tear
my bow tie, which
is that red thing
you see on my
school uniform.
My euphonium is
made of brass, an
alloy which is the
product of a
physical change.

▪ Chemical changes are usually irreversible. Chemical changes are a
result of chemical interactions. When matter interacts with heat,
light or electricity, chemical changes occur. Chemical changes also
occur when two or more different kinds of matter interact. Usually,
during a chemical change, energy in the form of heat or light may
be taken in or given out. Chemical changes can be represented
with word equations which takes the following form: Reactant ->
Condition -> Product.
A chemical
change I see is
when I am
baking cakes.
Brass is not
the product
of a
chemical
change.

▪ An example of a chemical reaction is the burning of charcoal
during a barbeque.
I don’t like
barbeque,
though.

▪ The products of a chemical reaction have different properties from
that of the reactants. Chemical energy stored in the charcoal is
converted to heat and light energy. Another example of a chemical
change is the formation of plastic from various war materials such
as crude oil. Plastic is found in objects that we use every day. Thus,
chemical changes occur all around us.
I use plastics
everyday. My
bottle is made
of plastic.

Types of Chemical Changes
▪ During occasions such as NDP, 4th of July, etc., light sticks are
often used. The changes within the light stick is an example of a
chemical change that is produced when mixing substances.
I only use light
sticks when I
am in USA or
Singapore on 4
July or 9
August.

Interactions between matter when mixed
▪ Mixing substances also produce other chemical changes. For
example, baking soda produces chemical changes when it is
mixed with some substances. Baking soda is used on several
objects because of its reaction with the substances. We can clean
coffee or tea-stained cups by using baking soda paste.
I’d use that if
I were British
and I were to
drink tea. I am
Japanese, so I
don’t drink
tea, I eat rice
and sushi.

Interactions between matter when mixed
▪ Many chemical changes, such as those, help us to improve our
lives.
I like
chemistry.

Interactions between matter and heat
▪ When we cook an egg, a chemical change occurs.
I love
cholesterol!

Interactions between matter and heat
▪ This process is a chemical change as the reaction is irreversible.
Heat interacts with different substances to bring about many
different kinds of changes.

Thermal decomposition
▪ Traditionally, we make candy by heating sugar until it melts.
However, if we heat sugar for too long, the sugar breaks down to
form black carbon and water vapor. This process is known as
thermal decomposition. Thermal decomposition is an example of
a chemical change brought about by heat. Thermal decomposition,
a process in which a substance is broken down into two ore more
simpler substances by the effect of heat, is a chemical change as
new substances are formed.
Diabetes is a
result of too
much sugar in
the body.

Thermal decomposition
▪ In the production of glass, thermal decomposition of limestone is
an important process. Limestone is mainly made up of calcium
carbonate. When heated, calcium carbonate in limestone breaks
down to form calcium oxide and carbon dioxide. This process is a
chemical change as calcium carbonate has interacted with heat to
form new products.
The windows of
my house are
made of glass.
But, the windows
of my car are
made of
plexiglass to
reduce weight.

Interactions between matter and oxygen
▪ Besides interacting with heat, matter can also interact with
oxygen. When we expose objects such as bicycles and chains to
the environment for long periods of time, parts of these objects
may turn rusty as they are made of iron or steel. Such objects
become rusty when the iron or steel reacts with oxygen in the
presence of water or moisture. Rusting is an oxidation process.
My car doesn’t
rust because it
is made of
titanium, which
is lighter than
iron or steel.

Interactions between matter and oxygen
▪ Oxidation refers to a process in which a substance reacts with
oxygen, causing chemical changes. These types of chemical
changes are oxidation reactions. They can also occur during
combustion and cellular respiration.

Combustion
▪ When we cook, natural gas burns in oxygen to release a lot of
heat, which is used to cook the food. The combination of natural
gas with oxygen is an example of combustion, which refers to the
combination of a substance with oxygen in the presence of heat.
One or more new substances may be produced. Many processes
around us involve combustion. Some examples of combustion
include the burning of fuels such as coal, natural gas, petrol and
diesel. Combustion usually releases high amounts of energy. The
energy released can be used for cooking, transport, producing heat
and generating electrical energy in power stations.
Even my car
needs
combustion. And
can you please
excuse me? I
need to go to
the toilet.

Combustion
▪ Complete combustion occurs when there is an abundant supply of
oxygen. For example, in car engines, petrol burns in oxygen to
produce carbon dioxide and water vapor. Chemical energy stored
in the petrol is converted to heat engine.
My car’s engine is a
large displacement
V12 quad turbo engine
called the L1078, a
huge improvement
from the L539, the
stock engine for my
car. Please!!! I need to
go to the toilet!!!

Combustion
▪ Besides the burning of fuels, other examples of combustion
include the burning of carbon and sulfur. In the burning of carbon,
carbon reacts with oxygen to produce Carbon Dioxide.
I NEED TO GO
TO THE
TOILET!!!!

Combustion
▪ Combustion of sulfur occurs in power stations and factories. Coal
and oil, which naturally contain sulfur, are burnt at these places.
The burning of sulfur in air produces a colorless and pungent gas
with a choking smell. This gas is sulfur dioxide. Sulfur dioxide can
contribute to acid rain.
Uh oh, I should
have gone to the
toilet earlier.
Anyways, sulfur is
very disgusting.
Please, don’t
breathe in sulfur.
And can I change
my clothes?

Cellular respiration
▪ We need energy for movement and survival. In order to get energy
from the food we eat, our body cells need to carry out cellular
respiration. Cellular respiration, the process in which living cells of
plants and animals take in oxygen to release the energy stored in
glucose, is a very important oxidation reaction that takes place in
the cells of living things.

Cellular respiration
▪ In cellular respiration, glucose and oxygen react in the cell to form
carbon dioxide and water with the release of energy. Hence,
cellular respiration is a chemical change. Chemical energy stored
in the glucose is converted into other different forms of stored
energy.
I have
finished
changing. I
also need
cellular
respiration.

Interactions between matter and light
▪ Light interacts with matter around us to cause chemical changes
to take place. Chemical changes are found in photosynthesis and
X-ray film.

Photosynthesis
▪ Photosynthesis, the process in which green plants make food in
the presence of light, is very important in that it ensures the
survival of living things on earth. During photosynthesis, green
plants use the energy from sunlight to make food in leaves.
Photosynthesis is a chemical change as the reactants, carbon
dioxide and water, react in the presence of sunlight and chlorophyll
to form the products, glucose and oxygen.
I have lots of
plants in my
garden.

X-ray film
▪ X-ray films, which consist of chemicals containing silver bromide
crystals, which are converted into silver by x-rays and light, that are
coated on a thin plastic base, are sensitive to x-rays, which are very
similar to light rays. They are used to observe the internal
structures such as bones, of a person’s body. This process is a
chemical change as silver bromide has interacted with x-ray and
light to form new products.
I have gone
for an x-ray
screening
before.

Interactions between matter and electricity
▪ Passing an electric current through a substance also produces
some chemical changes, which are produced during electrolysis
and electroplating.
You should
have learnt
about
electrolysis
and
electroplating
in Chapter 13.

Electrolysis
▪ When an electric current passes through some substances, the
substances are broken down into simpler substances through a
process known as electrolysis, the chemical decomposition of
substances with the passage of an electric current.

Electroplating
▪ Coins and trophies are sometimes covered with a very thin layer of
metal to make them more attractive. The metal layer may also
prevent the coins and trophies from rusting. This is done through
the process of electroplating. It is irreversible and is considered a
chemical change.
I got a trophy
before.

Types of Chemical Changes – Interactions
between Matter
▪ A group of substances, acids and alkalis, undergo chemical
changes when mixed with other substances.

Acids
▪ Acids are found in many things around us. Some acids can be
found naturally in living things like citrus fruits, which taste sour
because they contain citric acids. Other acids are made in
industries and are used daily for various purposes.
My car’s
battery uses
acid. I do not
like to eat
lemons. Yuck!

Acids react with some metals
▪ Decorative patterns can be carved onto metal objects using a
technique called acid etching. This technique relies on the reaction
of acids with metals such as copper, zinc or steel, which reacts
with acid to produce a salt and hydrogen gas.
I’m not trying
that.

Acids react with carbonates
▪ During food preparation, we also make use of the reaction of acids
with substances. An example of this takes place during bread-
making, in which a dilute acid reacts with a carbonate to produce
a salt, carbon dioxide and water.
I eat rice, not
bread.

Alkalis
▪ Alkalis are also found in many things around us. The presence of
an alkali causes solutions to taste bitter and has a slippery feel. It
is commonly found in soaps and liquid detergents. They react with
other substances to produce chemical changes,
I always use
soap to clean
myself.

Neutralization
▪ Acid is formed when bacteria feed on the food particles present on
our teeth. This may lead to tooth decay. To prevent tooth decay, we
must brush our teeth with toothpaste regularly. When alkalis react
with acids, a chemical reaction called neutralization occurs. Many
neutralization reactions can benefit us.
I always brush
my teeth.

Indicators
▪ Most acids and alkalis are colorless solutions. We can tell whether
they are acidic or alkaline by using an indicator, a substance which
changes color depending or whether the solution being tested is
acidic or alkaline. They usually exist as solutions, but they can also
be used in the form of indicator papers, which are prepared by
soaking filter paper in the solutions of the indicators.

Indicators
▪ Common indicators include red and blue litmus papers, and the
Universal Indicator.

Litmus paper
▪ Litmus paper is used to test if a solution is acidic or alkaline. The
effects of different types of solutions on blue and red litmus
papers are shown below.

Universal Indicator
▪ The Universal Indicator indicates the strength of acids through a
color change.

Movement of Atoms during Chemical Reactions
Atoms are neither created nor destroyed
▪ When a product is formed during a chemical reaction, its mass
remains the same as the mass of the reactants. Chemical
reactions involve the rearrangement of atoms that make up the
reactions and it can lead to the formation of new products.

▪ In Carbon Dioxide, the number of atoms remains unchanged after
the chemical reaction. The oxygen molecule is split up and
rearranged so that each oxygen atom now combines with the
sulfur atom to form a molecule of sulfur dioxide.

▪ In such changes, atoms are rearranged and not destroyed during
the chemical reaction. Hence, the mass of products in a chemical
reaction is equal to the mass of reactants in the same reaction.

Effects of Chemical Changes – Friends or Foes?
▪ Chemical changes affect our lives all the time and these effects
can be beneficial or harmful to us.

Benefits of chemical changes
▪ Many important processes around us are the result of chemical
changes. Natural processes such as decomposition,
photosynthesis, digestion, respiration, growth and reproduction are
all based on chemical reactions.

Harmful effects of chemical changes
▪ Chemical reactions may also bring harm to our health and the
environment.

Burning
▪ Burning and combustion in cars and factories release air
pollutants, such as soot and toxic gases, into the atmosphere.
I should be
placing a
catalytic
converter on
my car.

Rusting
▪ When iron rusts, structures such as bridges become corroded and
unsafe. These structures need to be repaired and replaced for
safety reasons. Rusting causes the loss of finite natural resources.
My car doesn’t
rust because
it is made of
titanium.

Decomposition
▪ Decomposition leads to wastage of food supply and resources.
Styrofoam
also
decomposes.

Effects of Chemical Changes – Friends or Foes?
▪ Understanding chemical changes has allowed humans to control
and make better use of them to improve the quality of life. This
has also influenced the way humans interact with the
environment. However, abuse of science and technology may lead
to problems such as acid rain which harms the environment.
I should make
my car hybrid
to reduce
emissions.

INTERACTIONS
INTERACTIONS WITHIN ECOSYSTEMS

Contents
▪ Ecosystems
▪ Energy Flow in an Ecosystem
▪ Decomposers
▪ Conserving the Environment
Back because of
Biology

Ecosystems
▪ In any habitat, we usually find more than one kind of organism. A
group of organisms of the same kind is called a population. The
different populations living together in the same habitat form a
community. All organisms interact with other organisms and with
their environment. When different communities of organisms
interact with one another and with their environment, an
ecosystem is formed. The environment of an organism can be
classified into two categories – the physical environment and the
biotic environment.
I am an
individual.
The
population is
my hometown.

Physical environment
▪ The place where an organism lives is its habitat. Every habitat has
its own unique physical environment. The physical environment is
determined by light, temperature, water, air, mineral salts and
salinity, and ph levels.
My habitat is
my house.

Physical environment
▪ The physical environment of each habitat determines the kinds of
organisms that live there. Some organisms have special features
or behave in certain ways to help them survive in their habitat. We
say that these organisms adapt to their environment.
Fact: The Asian Tiger
Snake is both Venomous
and Poisonous. It has
venom in its fangs for
killing its prey to eat, and
poison for defending itself
against predators. It gets
its poison from the toads it
eats. It then secretes its
toxins from glands on its
neck.

Light
▪ Plants need light to make food through photosynthesis. Most
plants are adapted to receive as much sunlight as possible.
However, some plants such as mosses and ferns grow better in
moist shaded areas. The amount of light available determines the
kinds of plants and hence, the kinds of animals found in a habitat.
Us humans also
need light
because in the
dark, we cannot
see things. Plus,
I need to go to
the toilet.

Temperature
▪ Temperature affects the activities of all organisms. In plants, low
temperatures slow down the rate of photosynthesis. Hence, the
growth of the plant is stunted. In animals, low temperatures slow
down blood circulation. Hence, the animal becomes sluggish. Most
plants and animals can survive in temperatures between 0 and 45
degrees Celsius. Some organisms, however, adapt to survive under
more extreme temperatures.
We have a body
temperature of
37 degrees
Celsius. And can
you excuse me?
I need to go to
the toilet.

Water
▪ All organisms need water to survive. The amount of water in any
place depends on the amount of rainfall it receives throughout the
year. In general, more organisms can be found where water is
available. Some organisms, however, adapt to survive in habitats
where there is a limited supply of water. One such habitat is the
desert.
I’m Back. What
a relief. I’ve
been to the
Sahara desert
before. I was
sweating a lot. I
was so thirsty.

Air
▪ Air is made up of gases that organisms need to survive. Plants
need carbon dioxide to carry out photosynthesis. Most land
organisms need oxygen to carry out respiration. Land organisms
take in oxygen from the air, while most aquatic organisms take in
oxygen that is dissolved in the water. Polluted water usually
contains less dissolved oxygen than fresh, clean water. As a result,
many fishes die in polluted water due to lack of oxygen. However,
some organisms, such as certain bacteria, adapt to survive in low-
oxygen habitats.
Most people
think that
breathing and
respiration are
the same. But,
in reality, they
are two
different
processes.

Mineral salts and salinity
▪ Mineral salts are important in the production of many essential
substances such as proteins, vitamins and chlorophyll. Plants and
animals do not grow well if they lack mineral salts. Plants obtain
mineral salts through absorption of the soil. Animals obtain
mineral salts from the food they eat. The amount of mineral salts
dissolved in the water affects the salinity of the environment.
Some aquatic organisms adapt to live in very salty water such as
the sea. Others adapt to live in streams and freshwater ponds.
I even need
mineral salts. I
am a living thing
of course. I am
a human.

pH (acidity/alkalinity)
▪ Both land plants and aquatic organisms are sensitive to the Ph
level of their respective habitats. Most organisms cannot survive in
environments that are too acidic or too alkaline. Land plants
cannot absorb the mineral salts from the soil if the soil is too
acidic. Freshwater organisms can tolerate a pH of about 7, which is
neutral. Marine organisms can tolerate a pH about 8, which is
slightly alkaline. Aquatic plants can affect the Ph level of water
during different times of the day. In strong daylight, aquatic plants
use the dissolved carbon dioxide in water to carry out
photosynthesis. This makes the water more alkaline.
You can test the
acidity levels or
alkaline levels
with a strip.

Biotic enviornment
▪ In a habitat, the survival of an organism depends on the physical
environment as well as the biotic environment. The biotic
environment refers to all the organisms in a habitat. These
organisms cannot survive alone. Each organism interacts with
other organisms in various ways. Some organisms hunt others for
food. Others provide shelter and protection to other organisms. All
these organisms compete for resources such as light, water and
shelter. These interrelationships between the organisms keep the
balance in the habitat.
I am part of the
biotic
environment.

Parasitism
▪ Parasitism is a relationship between the two organisms in which
one benefits at the expense of the other. A parasite normally does
some harm to its host.
Some parasites
can even kill
their hosts.

Mutualism
▪ Mutualism is a relationship between two organisms in which both
organisms benefit from each other.
When I was in
the garden, I
saw a bee on a
flower. This is
an example of
mutualism.

Predator-prey relationship
▪ An animal that lives by killing and eating other animals is called a
predator. An animal that is killed and eaten by a predator is called
a prey.
Some animals
are both
predators and
prey. But for
humans like me,
we are at the
top of the food
chain.

Types of ecosystems
▪ There are many types of ecosystems in the world. Some examples
of ecosystems are tundras, grasslands, deserts, rainforests,
seashores, coral reefs, oceans, swamps, and ponds. The earth
itself can be regarded as one big ecosystem called the biosphere.
The nearest
ecosystem to
me is the woods.

Energy flow in an ecosystem
▪ All organisms need energy to carry out life processes. They obtain
this energy from the food they take in.
Even I need
energy.

▪ In natural ecosystems, complex food relationships called food
webs exist. A food web is made up of interlinked food chains. Each
plant and animal in a food web may be part of several food chains.
Humans are also
part of the food
web.

▪ A food chain shows the feeding relationship between organisms.
We humans are
also part of the
food chain.

Energy loss in food chains
▪ The amount of energy that flows through an ecosystem does not
remain constant. The total amount of energy decreases
continuously along the food chain. The energy present in each
level of the food chain can be expressed through a pyramid of
energy.
Humans like me
are also in the
energy pyramid.

Balance in an ecosystem
▪ The presence or absence of one kind of organism can affect the
physical and biotic environments of a habitat. In a balanced and
stable ecosystem, the population sizes of the predators and their
prey remain relatively unchanged. Any change in the relationship
between the organisms can affect other organisms directly or
indirectly.

Balance in an ecosystem
▪ The balance of an ecosystem can be upset in the following ways:
▪ Introduction of new animals and plants into the habitat.
▪ Disease outbreaks.
▪ Human activities such as deforestation and overfishing.
I should stop
fishing from
now because it
can save the
marine animals.

Respiration and photosynthesis
▪ Respiration and photosynthesis are important processes in the
flow of energy in any ecosystem. Respiration releases energy
stored in food. Photosynthesis, on the other hand, makes energy
from the sun available to the other organisms.
Photosynthesis
does not occur
in me, but
respiration
does.

Breathing
▪ The oxygen needed for aerobic respiration is taken in by an
organism. Organisms with lungs take in and give out gases
through the process of breathing.
If I don’t
breathe, I will
die.

Decomposers
▪ Aside from photosynthesis and respiration, the breaking down of
complex nutrients is another important process in an ecosystem.
Micro-organisms such as bacteria and fungi play a significant role
in this process of decomposing nutrients. Fungi and bacteria are
the most efficient decomposers on earth. Decomposers are
organisms that break down the complex nutrients in feces and
dead bodies of plants and animals.
Decomposers
also decompose
non living things.

Conserving the enivronment
▪ Diseases are effects of a polluted physical environment. All
organisms depend on the physical environment for air, water and
food. Thus, we must take care of our physical environment.
I sometimes get
sick.

Need for conservation
▪ Human activities such as deforestation, fishing and farming
benefit us and provide us with homes and food. However, these
activities can also harm the environment. As human activities
continue to harm the environment, it is now more urgent to protect
and preserve the environment. Protecting and preserving the
environment is called conservation. Conservation is important for
many reasons:
▪ Conservation reduces global warming and disruption of natural cycles.
▪ Conservation protects different kinds of plants and animals including
marine life.
▪ Conservation ensures the preservation of tropical rainforests.
I can
participate in
conservation
activities.

OPTIONAL FOR N(A) – Saving the environment
through sustainable living
▪ Around the world, many people are trying to achieve a better
standard of living without harming the environment. The idea of
this lifestyle is to meet our present needs without depleting the
resources of the environment. This is to ensure that these
resources will still be available to future generations.
Normal
Academic
must know!

Terrace farming
▪ Farmers in countries such as Thailand practice terrace farming.
Farmers plant crops in terraces or a series of step-like benches.
This prevents erosion as water run-off is slowed down in each level.
Farmers also avoid the use of pesticide. Instead they use
organisms that control the crop-destroying pests. By doing so, they
avoid polluting the soil with chemicals.
Normal
Academic
must know!
I saw lots of
terrace farms
in China.

Wind turbines
▪ In Denmark, wind turbines are used to produce electricity. Turbines
convert kinetic energy in wind to electricity. This method of
producing electricity does not release greenhouse gases. Wind
energy relies on wind, a source of renewable energy. Fossil fuels
such as coal and natural gas are not needed. Thus the harmful
effects of obtaining fossil fuels and converting them into energy
are avoided. These harmful effects include water pollution and
land degradation.
Normal
Academic
must know!
There are also
offshore wind
turbines.

The End!
SCIENCE IS FUN!
Mr Naszry’s guns (Mr Naszry
is my science teacher)
See you
next
time!

Secondary 2 science revision

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