New Science Connection Textbook P.1-P.6 Sample Chapter

MarshallCoCpayvriegnhditsh1. The Human System

Did you know that the
different systems in our
body work together to

help keep us alive?

What happens to
the food that we eat?
How is the oxygen we
breathe in transported

in our body?

The Human System 1

Let’s Look at...

• the human digestive system
• the human respiratory system
• the human circulatory system
• how these three systems work together
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Cells make up the entire human body. Cells can be
grouped together to form a tissue which performs a
single function. Examples of tissues include connective
tissue, muscle tissue and nervous tissue.

Several different tissues that are grouped together
to carry out a single function is known as an organ.
Your heart is an example of an organ. It comprises
connective, muscle and nervous tissues.

Different organs work together in an organ system.
They work together to perform functions such as
digesting food (digestive system) and moving the body
(muscular, nervous and skeletal systems). Let us look at
some of the various organ systems in our body.

Cells Tissues Organs

1.1 The digestive system

Food gives us energy and keeps us alive. Have you ever thought
about what happens to the food you eat? Does it remain in the
same form after it enters your body?

The food we eat must be broken down into simpler
substances called nutrients. The nutrients can then be
absorbed into the blood and used by our body.

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The breaking down of food into simpler substances is called digestion. It is a complex
process that involves more than one organ. It is carried out by the digestive system.

Look at the diagram of the digestive system WOW!
and identify all the parts you know.

Mouth Salivary Did you know that if the entire
Tongue glands digestive system was stretched
out, it would be almost seven
Gullet metres long?
(oesophagus) This extremely long digestive
system can fit into your body
because the long intestines
are coiled to save space.
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Liver Stomach
Gall bladder Pancreas

Small Large
intestine intestine

Our digestive system Rectum
Anus

The human digestive system is made up of different organs connected together to
form a long passage. This passage begins at the mouth and ends at the anus.

The main parts of the digestive system are the mouth, gullet, stomach, small intestine,
large intestine and anus.

Mouth Canine

The digestion process begins in the mouth. In the
mouth, knife-like teeth called incisors in the front of the
mouth cut and slice the food into small pieces.

The premolars and molars help to grind the food into Molars
small pieces of food. Premolars

Saliva helps to soften and digest the food. Incisors

The tongue mixes the food with the saliva and rolls
it into small balls to be swallowed.

The Human System 3

Have you ever wondered why we have a sweet taste in our mouth after eating
certain food like rice and bread?

Some of the food we eat is not only broken down into smaller pieces but also
digested in the mouth. The saliva contains enzymes. Enzymes are special substances
in our bodies that help to break down bigger nutrients into smaller ones. For example,
in the mouth, some of the starch nutrients in the food we eat like rice and bread,
are not only broken down into smaller rice and bread pieces but also into smaller
nutrients like simpler sugars.
MarshallCoCpayvriegnhditsh
Going Further

Besides helping to mix the Sweet Salty Sour Bitter
food in our mouth with saliva,
our tongue also allows us to
taste food. The tongue has
several thousands of taste
buds on its surface to allow
tasting of sweet, sour, salty
and bitter food.

Taste areas on the human tongue

Gullet

When we swallow food, the small balls of food are pushed down a narrow muscular
tube called the gullet. This tube connects the mouth to the stomach.

Space Food
inside the Stomach
oesophagus
(gullet) Food moving down the oesophagus (gullet)

Muscles contract
and relax, pushing
the food forward

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MarshallCoCpayvriegnhditsh Put on Your Thinking Cap

The gullet pushes food down by muscular
contractions. When we are standing
upright, gravity also helps to pull the food
down. Can the food move down the gullet
into the stomach if there is no gravity?
How do astronauts eat in space where
there is no gravity?

Try This!

Try hanging upside down and
eating a small piece of bread.
Can you do it? Must you be
standing straight up to be able
to swallow the bread?

The Human System 5

Stomach

In the stomach, food is churned into
smaller pieces and mixed with digestive
juices. Digestive juices contain enzymes
that break down bigger nutrients into
smaller nutrients so that they can easily
dissolve in water. After two to five hours,
the solid food is changed into a liquid
form. The diagram below shows how
the stomach looks like on the inside.
MarshallCoCpayvriegnhditsh
The partly digested food then Food
leaves the stomach and enters
the small intestine.

Going Further

Stomach ulcers can Stomach
sometimes form in the
stomachs of people. The
digestive juices produced by
the stomach are very acidic.
The acid can weaken the
lining of the stomach, allowing
bacteria to attack the walls of
the stomach. This results in the
formation of a stomach ulcer.

Solid food is changed

Small intestine into a liquid form

The small intestine connects Small intestine

the stomach to the large intestine.

The small intestine is about 4 to 6 m

long and about 2.5 cm to 4 cm wide.

The small intestine is coiled so that it can
fit inside the abdomen.

In the small intestine, more digestive juices
are added to the food to complete the digestion process. Digestive juices in the
intestine contain enzymes that break down larger nutrients like starch, protein and
fats into simpler forms.

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The walls of the small intestine have a large surface area
to absorb nutrients. The nutrients pass through the walls
of the small intestine into the bloodstream. The blood
carries the digested food substances around the body.

Large intestine and anus

Food that is undigested in the small intestine
enters the large intestine. In the large
intestine, water and vitamins are absorbed.
The remains are temporarily stored in the
lower part of the large intestine called the
rectum.

The remains, also known as faeces, are
passed out from the body through the anus.
MarshallCoCpayvriegnhditsh Large
intestine

Undigested
food

Rectum
Anus

Large intestine

Key Ideas Digestive system
is made up of

mouth gullet stomach small large anus
where where where intestine intestine where

wwhheerree where

food is food passes food is digestion is water and faeces
cut into from the churned completed vitamins passes
smaller and nutrients out of
pieces and mouth to the and are absorbed are the body
digested stomach digested absorbed

Go to WB Activities 2.1 & 2.2

The Human System 7

1.2 The respiratory system

The human respiratory system is made up of several different organs working
together to enable us to breathe.

We breathe in and out through
the nose.

There are fine hairs in the
nose to trap dust in the air that
we breathe in. The mucus
produced by the nose also
helps to trap dust and bacteria.

The nose also contains smell
receptors to allow us to
recognise various scents.
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The windpipe is one of the air tubes that We have a pair of lungs. In a fully grown
carry air around the respiratory system. adult, each lung can hold about three litres
The windpipe connects the back of the of air.
mouth and nose to the lungs.
The windpipe branches into two separate In the lungs, oxygen from the air we breathe
pipes, one to each lung. The windpipe is in is absorbed into the bloodstream. Carbon
also lined with fine hairs to trap dust. dioxide produced by the body moves into the
lungs to be removed from the body.
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Put on Your Thinking Cap

Why is it more advisable to breathe through your nose
than your mouth when you are in a dusty environment?

MarshallCoCpayvriegnhditshWOW! sugar (glucose)
The oxygen that is taken in
The air we by the respiratory system +
breathe in is required for converting
contains about digested food into energy. oxygen
21% oxygen, This process takes place in
while the air all the cells and is known as carbon dioxide
we breathe out aerobic respiration.
contains 16% +
oxygen. We do
not use all the water
oxygen we take
in for each breath. +

energy

The Human System 9

Going Further

The lungs are made up of many tiny air sacs known as
alveoli (singular: alveolus). These air sacs help to increase
the surface area to volume ratio for more efficient
exchange of gases.

It is estimated that when the air sacs are spread out in
a single layer, they could easily cover a tennis court.
MarshallCoCpayvriegnhditsh
Trachea

Lung Capillary
network Alveolus

Bronchiole

Aorta

Superior
vena cava

Heart Pulmonary Alveoli Oxygen enters
artery alveoli
Key Ideas Carbon dioxide
leaves veins

Respiratory system
is made up of

nose windpipe lungs
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Go to WB Activity 2.3

1.3 The circulatory system

Our body has an efficient transport network to carry nutrients, digested food, oxygen,
carbon dioxide, water and other materials to where they are needed or removed.
This transport network in humans is called the circulatory system.

The circulatory system is also called the cardiovascular system. The word ‘cardio’
means ‘heart’, and ‘vascular’ means ‘tube’.
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Blood vessels
Blood vessels are tubes that carry blood
from the heart to the rest of the body and
back to the heart again.

Capillaries

Artery

Vein

The circulatory system is made up of the blood, blood vessels and heart. An important
function of the circulatory system is to pump freshly oxygenated blood throughout
the body.

The Human System 11

Blood

Blood flows around the body in the blood vessels.

Blood carries oxygen, digested food, water and
nutrients needed by our body. It also carries waste
materials such as carbon dioxide. Blood is made up
of four main components, namely the plasma, red
blood cells, white blood cells and platelets.

White blood cells are involved
in the defense of the body
against foreign invaders such
as bacteria and viruses.
MarshallCoCpayvriegnhditsh
Plasma makes up the bulk of
the liquid portion of the blood.
Nutrients, digested food and
carbon dioxide are transported
in the plasma.

Red blood cells
carry oxygen and
carbon dioxide.

Platelets are cell fragments which
are required for blood to clot.

Going Further

Do you know why blood is red in colour? This red colour is due
to the red blood cells. Red blood cells have a pigment called
haemoglobin. This pigment allows the red blood cells to
transport oxygen. When haemoglobin binds to oxygen, it forms
oxyhaemoglobin, which is a bright red colour.
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Blood vessels

Blood flows through all parts of our body through tubes called blood vessels.
There are three main types of blood vessels in our body. They are the artery, vein
and capillary.

Capillary

MarshallCoCpayvriegnhditshArtery Vein

Capillary

The arteries carry oxygen-rich blood away from the heart. They have thick, muscular
walls to withstand the high pressures.

Blood vessels further away from the heart have smaller,
thinner branches known as capillaries.

Capillaries supply blood to all parts of the body. The walls
of capillaries are only one-cell thick. This allows nutrients,
oxygen and carbon dioxide to pass through easily.

Blood from the capillaries flows to the veins. Veins carry
blood back to the heart. They are thinner and have less
muscular walls than arteries because blood pressure in the
veins is lower.

Capillary network in the eyeball

Going Further

What happens when you cut yourself? Do you notice that you
stop bleeding after a while? This is because the blood has clotted.
The process of blood clotting is known as coagulation.
Coagulation involves mainly platelets and other components
in the plasma. It helps to stop damaged blood vessels from
bleeding. If not, a person could bleed to death!

The Human System 13

Try This!

Place your fingers on your wrist and try to feel for a pulse.
The pulse you feel is actually the walls of the arteries
stretching during each heart beat. The blood from the heart
is pumped at great pressure out of the heart. This pressure
stretches the artery walls, giving rise to your pulse.
Using the thumb and index finger of your left hand, press the tip of your right index finger
and hold for two seconds. Release the pressure and observe the tip of your right index
finger. Do you notice that the tip of your right index finger appears to be white immediately
after the pressure is released? It then becomes pink again. This is because blood flow
through the capillaries was stopped for a while by the pressure, but resumed when the
pressure was released.
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Heart

The heart is a hollow muscular organ that lies in the chest. The heart pumps blood
through the blood vessels to all parts of the body.

The heart consists of four chambers. The top two chambers are called the atria
(singular: atrium) while the lower two chambers are called the ventricles
(singular: ventricle).

Put your hand on your chest and press lightly. Can you feel your heart pumping?

To lungs To rest of the body

Right atrium Left atrium

The right The left atrium
atrium receives receives oxygenated
deoxygenated blood blood from the lungs.
from around the body. When the left atrium
When the right atrium contracts, it pushes
contracts, it pushes the blood into the
the blood into the left ventricle. The
right ventricle. The left ventricle then
right ventricle then contracts to pump
contracts to pump oxygenated blood to
blood towards the the rest of the body.
lungs for it to be
reoxygenated. Right ventricle Left ventricle

With each squeeze, one ventricle pushes about 70 ml of blood into the blood vessels.
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Put on Your Thinking Cap

The heart is unlike any other muscle in the
body. Unlike skeletal muscles which you can
control, the heart muscles cannot be voluntarily
controlled. The heart also does not stop beating
once it is formed in the foetus. Why is this so?

MarshallCoCpayvriegnhditsh Go to WB Activity 2.4

Key Ideas

Circulatory system
has the

following parts

blood blood vessels heart

carries nutrients and pumps blood through
wastes around the body the blood vessels

arteries veins capillaries

The Human System 15

Review Questions

1. In which part of the digestive system does digestion of food begin?
2. “The circulatory system is the only system required to transport oxygen around

the body.” Explain why this statement is wrong.
3. Name the three different types of blood vessels in the circulatory system.

Experiment Time!

Where are the taste buds for the various tastes located?

Process skills
observing, inferring, predicting, analysing, evaluating, investigating
What you need
Sugar, salt, lime, bittergourd, blindfold, spoon
Procedure and observations
1. Blindfold yourself and stick out your tongue.
2. Your friend will place small samples of food, one at a time, at the tip of your tongue.
3. Try to identify the sample of food placed on your tongue.
4. Repeat the experiment with food placed at different positions of the tongue.
Conclusion
Can you identify all the different food samples correctly when they are placed at the tip or
centre of the tongue? Explain your answer.
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Go to WB Revision Worksheet 1

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