New Creative Science Book 9

(iv) Trachea
The trachea or windpipe is about five inch long tube made of C-shaped hyaline

cartilage rings. They are lined with ciliated columnar epithelium. The trachea connects
the larynx to the bronchi and allows air to pass through the neck and into the thorax.
The main function of the trachea is to provide a clear airway for air to enter and
exit the lungs. In addition, the epithelium lining of the trachea produces mucus. This
mucus traps dust and other contaminants and prevents it from reaching the lungs.

(v) Bronchi and Bronchioles

At the inferior end of the trachea, the airway splits into left and right branches
known as the primary bronchi. The left and right bronchi run into each lung before
branching off into smaller secondary bronchi. The secondary bronchi carry air into
the lobes of the lungs. The secondary bronchi in turn splits into many smaller tertiary
bronchi within each lobe called bronchioles. They spread throughout the lungs. Each
bronchiole further splits into many smaller branches less than a millimeter in diameter
called terminal bronchioles. Finally, the millions of tiny terminal bronchioles conduct
air to the alveoli of the lungs.

(vi) Lungs

The lungs are a pair of large and spongy organs found in the thorax lateral to the
heart and superior to the diaphragm. The left and right lungs are slightly different in
size and shape due to the heart pointing to the left side of the body. The left lung is
therefore slightly smaller than the right lung and is made up of 2 lobes while the right
lung has 3 lobes.

The interior of the lungs is made up of spongy tissues containing many capillaries
and around 30 million tiny sacs known as alveoli. Alveoli end into small blood
capillaries. It is the site for exchange of oxygen and carbon dioxide.

Respiration Process
The diaphragm is the main respiratory muscle that contracts and relaxes to allow

air into the lungs. The muscles of respiration contract thereby expanding the chest
cavity. This causes a negative pressure within the pleural cavity (where the lungs are
housed) which forces the lungs to expand. The expansion of the lungs reduces the
air pressure in the lungs. This draws air from the environment which is at a higher
pressure. Air will flow from an area of high pressure to the low pressure. Air is drawn
through the nose. It gets ‘filtered’ and heated in the nasal cavity. It then passes down
the throat and enters into the trachea where it rushes into the bronchi. The bronchi
divide the air flow between the two lungs. The air then passes into smaller air tubes
known as bronchioles. The air enters the tiny air sacs within the lungs, called alveoli,
where oxygen crosses into the blood and carbon dioxide empties into the lung. The
respiratory muscles relax and the chest cavity contracts. The elastic lungs recoil and
push air out through the air passages where it is emptied into the environment.

New Creative Science, Class 9 | 297

However, this does not occur in isolation. The blood carries the oxygen to the
tissues by binding it to haemoglobin in the red blood cells. The heart pumps this
blood throughout the body ensuring that oxygen reaches all the cells. Simultaneously,
carbon dioxide is carried away by red blood cells towards the lungs where it can be
expelled. Cellular respiration takes place in the cells to release energy. Normally, an
adult person breathes 18-20 times in a minute.

Excretory System

All living organisms need energy to run their daily living activities. This energy
comes from the food. No life is possible without food. In the body of living beings,
food produces energy along with various by-products. The examples of by-products
are urine, stool, carbon dioxide, etc. Most of these by-products are useless as well as
harmful in the body. It is necessary to remove these by-products from the body. This
process is called excretion. Therefore, the process of removing waste and harmful
materials form the body is called excretion. The process of excretion is carried out by
the group of organs called excretory organs.

The excretory system is a system of organs that removes waste products from
the body. When cells in the body break down proteins, they produce wastes such as
urea. When cells break down carbohydrates, they produce water and carbon dioxide
as waste products. If these useless waste products are allowed to accumulate in the
body, they would become dangerous to the health. So, these useless waste products
are removed by a group of organs called excretory system. Therefore, the system of
the body which helps in excretion is called excretory system and the organs which
are present in the excretory system are called excretory organs. The kidneys are
considered the main excretory organs in the human body. They eliminate water, urea,
and other waste products from the body in the form of urine. The waste-containing
liquid that remains in the nephrons is called urine. Urine is 95 percent water, in which
the waste products are dissolved.

The kidneys are bean-shaped organs. They are located at the back near the spinal
column. The left kidney sits slightly higher than the right one. The size of an adult
kidney is approximately 4 inches (10 centimeters) long and 2 inches (5 centimeters)
wide. To maintain human life, it is necessary for at least one of the kidneys to function
properly.

Blood carries waste products to the kidneys via the renal artery. Inside each
kidney, blood is transported to 1.2 million filtering units called nephrons. The cells
in nephrons take in the liquid portion of the blood and filter out impurities lime urea,

298 | System

mineral salts, and other toxins. Necessary substances such as certain salts, water,
sugar, and other nutrients are returned to the blood stream via the renal vein.

A pair of tubes called ureters carries urine from the kidneys to the urinary
bladder. Each ureter is about 40 to 45 centimeters long. The urinary bladder is a
hollow muscular sac. It is located in the pelvis. It is collapsed when empty but pear-
shaped and expanded when full. The bladder in an adult can hold more than 0.6 liters
of urine. The bladder discharges urine into the urethra, a duct leading to outside the
body. In males, the urethra is about 20 centimeters long. In females, it is less than 5
centimeters long. A sphincter muscle around the urethra at the base of the bladder
controls the flow of urine.

Abdominal aorta Inferior Vena cava
Right Kidney Renal Artery

Left Kidney

Renal Vein Ureter

Urinary Bladder
Urethra

Urinary System

Other organs and systems in the body also play a part in excretion. They are
briefly described below.

Lungs

The respiratory systems including lungs, nose, and mouth eliminate water
vapour and carbon dioxide through exhalation (the process of breathing out).

Liver

Liver is an important organ excretion. It converts toxic ammonia into urea. It also
converts old and broken red blood cells into bile pigment.

Digestive System

The digestive system removes feces, undigested food, etc. by a process called
defecation or elimination. The organs involved in this process are large intestine,
rectum, anus, etc.

New Creative Science, Class 9 | 299

Skin

The skin also acts as an organ of excretion. It removes water, small amounts of
urea and salts as a sweat.

Importance of the excretory system
i. Excretory system helps to remove nitrogenous waste products like urea,
uric acid, etc.
ii. The waste products which are produced in the cells are carried out up to the
excretory organs through blood. After that, they are eliminated out.
iii. The metabolic by-products such as urea, carbon dioxide, etc. are removed
out through excretory organs.
iv. The kidneys are the main excretory organs. They play very important role to
remove useless materials through the body and they also return the useful
materials into the blood after filtering.

Transpiration

The loss of water in the form of vapour from the exposed parts of a plant is
called transpiration. The loss of water due to transpiration is quite high in plants. It is
2 litres per day in Sunflower, 36-45 litres in Apple and up to 1 tonne per day in Elm
tree. Rather 98-99% of the water absorbed by a plant is lost in transpiration. Hardly
0.2% is used in photosynthesis while the remaining is retained in the plant during
their growth. Most of the transpiration occurs through foliar surface or surface of the
leaves. It is known as foliar transpiration. Foliar transpiration accounts for over 90%
of the total transpiration. Young stems, flowers, fruits, etc. also transpire a lot. Mature
stems transpire very little.

ACTIVITY

Take 2 potted plants. Cover the shoot of one potted plant by using transparent polythene. Place
both of the plants in the sunlight for about few hours. After few hours you can observe some water
vapour or water droplets in inside surface of the polythene. This is due to transpiration in plants.

Types of transpiration

Depending upon the plant surface transpiration is of the following four types.

1. Stomatal Transpiration
It is the most important type of transpiration. Stomatal transpiration constitutes

about 50-97% of the total transpiration. It occurs through the stomata. The stomata
are found mostly on the leaves. A few of them occur on the young stems, flowers and
fruits. The stomata expose the wet interior of the plant to the atmosphere. More water

300 | System

evaporates from the internal cells to replace the outgoing water vapour. The stomatal
transpiration continues till the stomata are kept open. In most of the plants the stomata
remain closed at night. Therefore, plants do not transpire during the night.

2. Cuticular Transpiration
It occurs through the cuticle or epidermal cells of the leaves and other exposed

parts of the plant. In common land plants cuticular transpiration is only 3-10% of the
total transpiration. In herbaceous plants the cuticular transpiration may be up to 50%
of the total. Cuticular transpiration continues throughout day and night.

3. Lenticular transpiration
It is found only in the woody branches of the trees where lenticels occur. The

lenticular transpiration is only 0.1% of the total transpiration. It, however, continues
day and night because lenticels have no mechanism of closing and opening.

4. Bark transpiration
This type of transpiration occurs through corky covering of the stems. Bark

transpiration is very little but its rate is often more than lenticular transpiration due
to larger area. Like cuticular and lenticular types of transpiration, bark transpiration
occurs continuously during the day and night.

Importance of transpiration

i) Photosynthesis
It provides water for photosynthesis in the leaves.

ii) Cooling
Transpiration involves the evaporation of water. The cells in the leaves are
exposed to direct sunlight. Energy from the sunlight can be transferred from the
plant cells to the water causing it to evaporate. This causes the plant cells to cool
down and prevents direct sunlight from damaging the delicate cells.

iii) Support
The cells in a plant absorb water by osmosis and swell up. As a result of this it
creates turgor pressure and the cells are said to be turgid. Turgid cells are firm
and give support to the plant.

iv) Movement of Minerals
The water transported upward from the roots to the leaves also contains dissolved
mineral salts. They are used to produce a variety of substances such as proteins
in the plant.

New Creative Science, Class 9 | 301

v) Effect on water movement
The absorbed water is transported from roots to leaves through the xylem
vessels. This process is greatly influenced by the transpiration pull. Water loss
due to transpiration results in the development of low water potential in the leaf
tissues. Thus, water moves from the xylem vessels to the leaf cells and helps in
the ascent of sap.

vi) Development of mechanical tissues
Greater amount of transpiration helps in the development of mechanical tissues
in plants. The plants become healthier. As a result, plants become able to resist
the attack of fungi and bacteria.

vii) Increasing taste of fruits
The solutes inside the cells become more concentrated when transpiration is rapid.
The concentration of sugar solution in the cells of fruits increases the taste of fruits.
Transpiration is also known as a necessary evil because large amount of absorbed
water is lost during transpiration. It is harmful to plants. Also, unnecessary
wastage of energy takes place during the process of water absorption which is
lost due to transpiration. When the rate of transpiration is high in plants growing
in soil deficient in water, an internal water deficit develops in plants which may
also affect metabolic process.

ANSWER WRITING SKILLS

1. The cell is the structural and functional unit of life. Why?
Ü Living organisms are composed of cells. All the metabolic activities of the living

beings are performed inside a single cell. So, is the cell called the structural and
functional unit of life.

2. A bone dipped into acid becomes softer. Why?
Ü The bone is composed of the minerals like calcium, phosphorous, magnesium,

etc. They are supposed to make the bones hard. When a bone is dipped into the
acid, the minerals get dissolved into the acid making the bones porous and hence
become soft.

3. Why is the pelvis of a woman wider than that of a man?
Ü The pelvis of a woman is wider than that of a man to give space to keep the baby

during pregnancy and to make easy to pass the baby at the time of its birth.

4. The height of the plant doesn’t increase if its tip is cut. Why?
Ü The tip of the plant consists of apical meristem. By the division of these cells a

plant grows. When the tip is cut, the apical meristem is cut itself and hence the

302 | System

plant cannot grow.

5. Transpiration is also known as a necessary evil. Why?
Ü It is because the large amount of absorbed water is lost during transpiration.

It is harmful to plants. Also, unnecessary wastage of energy takes place. But,
transpiration is a biological process. It helps plants in many ways. If transpiration
does not occur in plants, the biological process gets affected badly.

SUMMARY

” The cell is the structural and functional unit of life.
” A tissue is the group of cells performing a specialized function.
” Plant tissues are divided as meristematic tissues and permanent tissues.
” Meristematic tissues have the capacity to divide and permanent tissues do not

have the capacity to divide.
” Meristematic tissues are again divided into various types according to their

origin, position, plane of division and function.
” Xylem and phloem are complex permanent tissues. They are also called

vascular tissues.
” Secretory and glandular tissues are special tissues.
” Bones are the hardest connective tissues of our body.
” The human skeleton consists of 213 bones in infants which get fused in adults

to form 206 bones.
” The human skeleton is divided into two types viz. axial skeleton and

appendicular skeleton.
” The bones of the skull, the vertebral column and thoracic cage constitute the

axial skeleton. It consists of 80 bones.
” The bones of the pectoral girdle, pelvic girdle, forelimbs and hind limbs

constitute the appendicular skeleton. It consists of 126 bones.
” The femur is the longest and strongest bone of the human skeleton.
” Digestion is a catabolic process or the process of breaking down of complex

food materials into simple forms which can be directly absorbed by the body.
” Most of the vertebrate animals have hard and bony structures in their mouth

which are called teeth.
” Respiration is the complex process of oxidizing the digested food materials in

the cells to release energy and carbon dioxide.

” The loss of water in the form of vapour from the exposed parts of a plant is
called transpiration.

New Creative Science, Class 9 | 303

EXERCISE

1. Define a cell, a tissue and an organ.

2. What are the functions and location of the following tissues?

(a) Apical meristematic tissue (b) An intercalary meristematic tissue

(c) Xylem (d) Phloem

(e) Parenchyma

3. Plant cells can prepare their own food. Why?

4. Label the different tissues of the given figures. Also, mention the function of these
tissues.

5. Define skeleton. Write its three functions.

6. What is a bone? Write its three functions?

7. Name the types of skeletons present in the human body.

8. What is digestion? Describe the human digestive system with a well-labeled diagram.

9. What is dentition? Describe the different types of teeth present in the human mouth.

10. What is respiration? Describe the respiratory system of the human body with a well-
labeled diagram.

11. Describe the respiratory process in a human body.

12. What is transpiration? Describe different kinds of transpiration.

13. Explain the importance of transpiration.

14. Mention the number of following bones in a human body.

(b) Bones of cranium (c) Bones of facial region

304 | System

(d) Bones of vertebral column (e) Bones of forelimbs
(f) Bones of hind limbs

15. Write the functions of: (c) Vertebral column
(b) Thoracic cage (e) Forelimbs
(d) Femur
(f) Skull

16. Give reasons:

(b) Bone dipped into HCl becomes soft (c) Joint ache occurs in old age.

17. Define:

(b) Transpiration (c) Digestion (d) Assimilation (e) Dentation

18. Write down one main difference between:

(b) Maxilla and mandible (c) Femur and humerus

(d) Carpals and tarsals (e) Digestion and respiration

A

B GLOSSARY
C

Voluntary : working according to our will
Straited : structure with bands
Articulate : communicative
Proximal : located towards the centre of the body
Distal : located away from the centre of the body
Stomata : the small pores present in the leaves of plant
Lypase : lipid digestive enzyme
Atlas: the rst vertebra of the backbone

New Creative Science, Class 9 | 305

UNIT

19 SENSE ORGANS

About the Inner Ear Introduction

The internal ear is made up We see the things around us and enjoy natural beauty.
of three parts: We hear sounds produced by different bodies. We feel
 Vestibule touch, pain, hotness, coldness, etc. We identify different
 Semicircular canals odours and taste which have different flavours. How
 Cochlea could these be possible? What are the parts in our body
Vestibule is the small, which are making aware us about the surrounding? The
rounded expanded and organs which detect and help to identify the changes in the
the central part which environment are called sense organs. The human body has
transmits the vibration five sense organs namely,
(sound waves) to the lower
part of the internal ear. (a) Eyes (b) Ears (c) Nose (d) Tongue (e) Skin
Semicircular canals are
three in number and they (a) Eyes (The organs of sight)
are arranged mutually
perpendicular to each other. A pair of eyes present in the orbital cavity of our skull
They are also concerned to are the organs of sight or vision in the human body. The
balance the body. eyes enable us to see around us and enjoy the pleasure of
Cochlea is a helix-shaped nature’s beauty.
structure. It has three
canals among which its The eyes are provided with photoreceptor cells which
middle canal is provided receive the visible light. The light stimulates the visual
with the hearing apparatus pigments present in the retina. It helps to form the image
called the organ of carti. of the object on the retina.
This organ sends the sound
impulse to the brain as it is Our eyes are protected from external injury, dust,
with the auditory nerves. insects, etc. with the help of eyelids and eyelashes. There
are also the tear glands or lacrimal glands at the upper
306 | Sense Organs side of each orbit towards its outer corner. It secretes the
salty and antiseptic fluid or the tears which keeps the eyes
moist, soft and make it free from bacteria and germs.

The human eyeball consists of three layers i.e.
i. Outer coat (sclerotic layer)
ii. Middle coat (choroid)
iii. Inner coat (retina)

i. Outer coat (sclerotic layer)
It is the outermost covering of the eyeball made up of dense connective tissue

fibres. It gives the mechanical protection and shape to the eyes. It consists of two
regions; the posterior region is known as the sclera and the anterior region is called
the cornea. The sclera is an opaque and white part. It gives shape to the eyeball and
protects the inner parts.

Similarly, the cornea is a small, thin and transparent layer which is covered by a
thin transparent membrane known as conjunctiva. The conjunctiva is supplied with
free nerve endings and blood capillaries. Sometimes, the conjunctiva turns red due to
the viral infection called conjunctivitis.

MEMORY TIPS

The cornea is not supplied with any blood vessels.

QUESTIONS >>
# Why are our eyes supplied with tear glands? What are the functions of tear?

ii. Middle coat (choroids)
It is the middle layer of the eye made up of thin layer of connective tissues. It

again consists of three parts i.e. choroids, ciliary body and iris.
The choroid lies in the posterior region of the sclera and in the frontal region it

forms the ciliary body. It is a pigmented and highly vascularized with blood vessels.
It helps in the total absorption of light due to its dark pigmentation. It also provides

New Creative Science, Class 9 | 307

nutrition to the retina.
The ciliary body consists of ciliary muscles by the contraction and relaxation

which helps in the adjustment in the focal length of the lens to produce a sharp image
on the retina.

The iris is the coloured pigmented thin muscular disc-shaped structure which
lies in the eyeball before the lens. The pupil regulates the amount of light entering
the eyes. In a bright light, the pupil becomes smaller to allow to enter only a small
amount of light whereas in a dim light, the pupil grows larger to allow maximum
amount of light for the proper visualization.

MEMORY TIPS

The iris gives colour to the eyes. Some people have black, some have brown, some
have green or blue eyes because of the pigmentation in iris.

QUESTIONS >>
# We cannot see at all for some time when we enter a dark room after staying in the bright

sunlight for some time. Why?

ACTIVITY

Ask your friend to show a glowing torchlight towards the pupil and ask him/her to observe the
change of the size of pupil of the eyes. Now repeat the same process in your friends’ eye and
observe the change in the size of the pupil of his/her eyes. What change do you see? Why?

Lens

Our eyes consist of a convex lens made up of proteins. The lens divides the
eyeball into two chambers. They are the aqueous chamber and the vitreous chamber.
The aqueous chamber is filled with aqueous humour which helps to refract the light
rays on the retina. Similarly, the vitreous chamber is filled with the vitreous humour
which gives the round shape to the eyes. The suspensory muscles present in the eyes
help in the contraction and relaxation of the lens to form the image of the objects
nearer or farther.

iii. Inner coat or Retina
It is a pigmented thick layer provided with many layers of nerve fibres or cells

known as photoreceptor cells. There are two types of photoreceptor cells i.e. rods
and cones. Rods are the rod-shaped photoreceptor cells which are sensitive to dim
light. So, they help us to see in the dim light. Similarly cones are the cone-shaped
photoreceptor cells which enable us to see in bright light.

Rods contain purple pigment known as rhodopsin (formed from vitamin ‘A’)
and cones contain violet pigment known as idiopsin (formed from vitamin ‘A’). So,
the deficiency of vitamin ‘A’ in rods causes night blindness and the deficiency of
vitamin ‘A’ in cones causes colour blindness.

308 | Sense Organs

In the retina, there are two points called a blind spot and a yellow spot. The blind
spot does not contain any photo receptor cells. So, no image is formed on it and thus if
the light from an object falls on the blind spot then we cannot see at all. But the yellow
spot contains only cones where shape of an image is formed.

MEMORY TIPS
 The yellow spot is also known as fovea.
 Colour blindness is a genetic disorder in which a person cannot distinguish

between red and green colours.

Working mechanism of human eye

When the light reflected through any object comes to our eyes, it passes through
the cornea and then enters the eyes through the pupil. The lens refracts the light so
that the rays meet on the retina and the real inverted and diminished image is formed
on the retina. The optic nerves present in the retina transfer these signals to the brain
and the brain interprets the signals and corrects the image to see the erect image of
the same size of the object.

Care of eyes

(i) We should wash our eyes with clean water regularly.
(ii) We should not give more stress to our eyes by reading and doing fire works in

the dim light.
(iii) We should not watch television from a nearer distance.
(iv) We should not rub our eyes and use an infected towel or handkerchiefs.
(v) In case of eye infection, we should consult doctors and use only the medicine

prescribed by them.
(vi) We should eat plenty of foods like fruits, vegetables, milk, fish, eggs, etc. to

supply vitamin ‘A’.
New Creative Science, Class 9 | 309

(b) Ears (the sense organs of hearing)

Ears are the sense organs which are concerned to the hearing sounds and
balancing our body. Ears are provided with two types of receptors i.e. phonoreceptor
(helps to hear) and stato receptors (helps in the balancing of the body). The human ear
can be divided into three parts:

i) External ear ii) Middle ear iii) Internal ear

Structure of ear

i) External ear
The external ear is the cartilaginous projection from the side of the head, which

consists of the pinnae and the external auditory canal.

The pinna is an expanded, funnel-shaped portion of the ear. It collects and directs
the sound waves to the external auditory canal.

The external auditory canal is a tube which leads to the ear drum or tympanum
or tympanic membrane. Its outer wall is hairy whereas the inner lining has ceruminous
glands which secrets earwax. It helps to direct the sound waves to the internal ear.

ii) Middle ear

It is also called the tympanic cavity,

which is connected to the pharynx

by an eustachian tube or the auditory

capsule. It consists of an eardrum or a

tympanum. The eardrum vibrates due

to the sound waves striking it. The Bones of the ear
middle ear also consists of three small

bones called ear ossicles. They are malleus, incus and stapes. The ear ossicles help to

increase the strength of sound waves and allow the vibration to the internal ear.

310 | Sense Organs

ii) Internal ear

The internal ear is made up of three parts:

• vestibule • semicircular canal and • cochlea

Bony labyrinth

Membranous labyrinth

Semicircular canals Ampulla of
semicircular canal

Anterior Utride
Posterior
Lateral Vestibule
Oval window
Saccule

LATERAL Cochlea
Ampulla of Cochlear duct
semicircular duct
Stapes in MEDIAL
oval window
Round window

The vestibule is the small, expanded and the central part, which transmits the
vibration (sound waves) to the lower part of the internal ear.

Semicircular canals are three in number and they are arranged mutually
perpendicular to each other. They are concerned to the balance of the body.

The cochlea is a helix-shaped structure. It has three canals, among which its
middle canal is provided with the hearing apparatus called the organ of corti. This
organ sends the sound impulse to the brain as it is with the auditory nerves.

Working mechanism of ear

When the pinnae receives the sound waves, it directs it to the auditory canal.
These sound waves now reach the middle ear where they vibrate the ear drum. Then
through the movement of ear ossicles, the sound reaches the cochlea, where the
waves create the fluid into motion. This stimulates the auditory nerve and impulse is
conducted to the brain. Then the brain interprets the sound.

Care of the ears

i. We should not insert sharp things like straw, keys, pencils, etc. inside the ears.
ii. For taking out earwax, it is necessary to make it moist by using glycerine

and use ear buds to take it out.
iii. We should consult an ear specialist if there is pain, bleeding or pus formation

inside the ears.
iv. We should protect our ears from the loud sound as it may rupture the

eardrum.

New Creative Science, Class 9 | 311

(c) Nose (the sense organ of smell)

The nose is the sense organ of smell. There is a nasal cavity inside the nose,
which is divided into two nostrils by a vertical septum. There are a large number
of chemoreceptors or olfactory nerves present in the inner lining of the nose, which
detect the various smells.

When the chemical with smell comes in contact with the olfactory nerves inside
the nasal chamber it stimulates the chemoreceptors or the olfactory nerves. The
stimuli are carried to the brain through these nerves, where the smell is recognized.

When a person gets cold, the chemicals cannot come in contact with the olfactory
nerves because the epithelium lining inside the nasal chamber is swollen so, he cannot
get the sense of smell.

QUESTIONS >>
# A person suffering from cold cannot recognize any smell. Why?

Care of our nose

i) We should not insert our fingers and sharp objects inside our nose.
ii) We should cover our nose during sneezing.
iii) In case of infection and wounds inside the nose, we should consult doctors.

(d) Tongue (the sense organ of taste)

The tongue is a muscular organ found inside the
mouth cavity, which gives the sensation of different
types of tastes. The tongue is provided with a number of
chemoreceptors (taste-buds).

There are special areas separated for different types
of tastes in our tongue.

i. The tip of our tongue is provided with sweet
taste receptors.

ii. The tip and sides of our tongue are provided
with salty taste receptors.

iii. The sour taste receptors are at the sides of
tongue.

iv. The bitter taste receptors are at the back side of
the tongue.

Care of the tongue

i. We should regularly clean our tongue at the time of brushing our teeth.

ii. Very hot and very cold food should not be eaten.

312 | Sense Organs

Skin (the sense organ of touch)

Skin is the outermost covering layer of our body, which gives us the sensation of
touch, pain, cold, heat, pressure, etc. Our skin is a combination of three layers. They
are:

i) epidermis ii) dermis iii) sub-cutaneous

Dermal papillae Pore Hair
Cold receptor Epidermis

Heat receptor Dermis
Blood vessel
Connective tissue Subcutaneous layer
Arrector pili muscle
Nerve Sebaceous gland
Sweat gland Sweat gland

Epidermis is the outermost layer, which has hairs, pores, nails, etc. Dermis
has blood vessels, nerve endings, glands etc. The nerve endings are also called as
tangoreceptors. Similarly, sub- cutaneous is the layer of fat and blood.

The skin protects the organs against injuries. It regulates the body temperature
and gives us the sensation of touch, pain, pressure, heat, etc.

Care of skin

(i) We must keep our skin clean by regular cleaning and bathing.
(ii) We should wear comfortable and sweat absorbing clothes.
(iii) In case of skin allergy or infection, we should consult a doctor.
(iv) We should not expose our skin to the direct UV-rays of the sun.
(v) Wounds and cuts should be treated with antiseptic liquids to prevent them

from infection.

ANSWER WRITING SKILLS

1. When we enter a dark room after staying in the sunlight, we cannot see
anything for some times. Why?

Ü When we were staying in the sunlight, the size of our pupil had been reduced to
allow to enter only a small amount of light. As we enter inside the dark room,
the pupil takes some time to accommodate to a large size. Hence, we cannot see
anything for some time.

New Creative Science, Class 9 | 313

2. We are given chocolate to chew while travelling by an aeroplane. Why?
Ü When the aeroplane takes height suddenly then the atmospheric pressure

suddenly reduces outside the eardrum. At that time, swallowing opens the
eustachian tube and air can pass from pharynx into middle ear cavity which
equalizes the air pressure on the both sides of the eardrum. This prevents the
disturbance of the eardrum by the difference of pressure on both sides of it.
Thus, we are given chocolate to chew while travelling by an aeroplane.

3. Salty taste can be felt faster than the bitter taste. Why?
Ü The receptors of salty taste lie at the tip of the tongue whereas that of bitter taste

lie at the back of the tongue. So, salty taste is felt faster than the bitter taste.

4. When we are suffering from cold, we do not identify any smell. Why?
Ü When we are suffering from cold, the epithelium of our nose is swollen, due

to which the chemicals coming from the smelly substances can not reach the
olfactory nerves. So, they can not be identified.

5. We cannot get proper flavour of food when we are suffering from cold. Why?
Ü Flavour is the combination of taste and smell in which both senses i.e. gustatory

and olfactory receptors are stimulated at the same time. Therefore, we cannot
receive the proper flavour of food when we are suffering from cold.

6. If a strong odour is felt for some time, the sensation of smell of that substance
is weakened. Why?

Ü When we smell a strong odour at first, it reacts with the chemoreceptors of
our nose and thus, we can identify it but as it is felt for a long time then the
chemoreceptors become familiar with it and thus, we cannot further identify it.

7. The blind spot is devoid of vision. Why?
Ü The blind spot is the place in the retina, which doesn’t contain any nerve cells.

So, if the refracted rays through the lens even meet at it, it cannot transfer any
stimuli to the brain and hence is devoid of vision.

SUMMARY
” The organs which make us aware about the surrounding are called sense

organs.
” There are five sense organs in the human body i.e. (a) eyes (b) ears (c) nose (d)

tongue and (e) skin
” The eye gives us the sensation of vision. It has three layers: the outer sclera,

middle choroid and inner retina.
” The retina consists of two spots i.e. yellow spot and blind spot.
” Ears are sense organs responsible for hearing and balancing.
” The ear is divided into the external ear, the middle ear and the internal ear.
” The tongue is the sense organ of taste which has many taste receptors in it.

314 | Sense Organs

” The receptors of sweet and salt are at the tip, that of sour are at the sides and
that of bitter taste are at the backside of the tongue.

” The nose is the sense organ of smell which is provided with many olfactory nerves.

” Skin is the sense organ, which gives us the sensation of touch, pain, heat,
pressure, etc.

” Skin is divided into three layers i.e. epidermis, dermis and sub-cutaneous layer.

” We should take good care of all our sense organs.

EXERCISE

1. What do you mean by sense organs? Name the sense organs found in the human body.

2. Describe the morphology of the eye with a neat and clear diagram.

3. Why does a person suffer from night blindness and colour blindness?

4. What are the visual pigments of rods and cones?

5. The blind spot is devoid of vision. Why?

6. What are the functions of the aqueous humour and the vitreous humour?

7. Name the parts of the middle ear with their functions.

8. One feels dizziness after spinning for a while. Why

9. Name the ear ossicles.

10. Why is salty taste felt faster than bitter taste?

11. What do you mean by taste buds?

12. When a person goes to bright sunlight from a dark room, his eyes dazzle. Why?

13. Write the functions of skin.

14. Write three methods of caring:

(a) eyes (b) nose (c) ears

15. Draw a neat diagram of a human tongue showing various zones of taste.

A

B GLOSSARY
C

Colour blindness : a genetic disorder in which the person cannot distinguish between red and

green colours

Receptors : organ that receives the sense

Lacrimal gland : tear gland

Optical nerves : the nerves of the eye which connect to the brain

Cone cells : the cells of the eye which are responsible to see in bright light.

Rod cells : the cells of the eye which are responsible to see in dim light



New Creative Science, Class 9 | 315

UNIT

20 EVOLUTION

About the Scientist Introduction

Gregor Johann Mendel The earth is the only planet in the solar system in
(1822-1884) which there is the existence of living things. The earth is
the habitat of millions of living things from unicellular,
Gregor Johann Mendel (1822- microscopic organisms to the gigantic species. Whenever
1884) was born into a peasant we see any living thing, we may wonder how such things
family of Maravia. Due to might have originated on the earth. Were they originated
poverty, he became a monk in in their present forms or were they different from their
1843 and later in 1847, was made present day forms? Were all the living organisms originated
an abbot (head) of Augustinian at the same time or were they originated one by one?
monastery of St. Thomas at
Brunn, Austria (now Bruna in According to the scientists, life was originated on the
Czech Republic). From here, he earth about 2000 millions years ago in its marine water.
went in 1851 to the University of Then, slowly they evolved into more developed and
Vienna, where he studied natural complex forms to the present day forms. Thus, evolution
history and mathematics for two is defined as the gradual and continuous change of living
years. He also became interested organisms from simpler forms to the higher and more
in the process of hybridization. complex forms. The process of evolution is so slow that we
Mendel returned to the monastery cannot feel it even in our lifetime.
in 1853 and also worked as a
teacher in a school. From 1856 to There are many hypotheses propounded by many
1865, Mendel conducted breeding scientists about the origin of the creatures on the earth but
experiments on garden pea plants none of them are fully satisfactory. The hypotheses can be
(Pisum sativum) in the garden of grouped into the following three groups.
his monastery. He published his
findings in 1866 in the ‘Annual (1) Theory of special creation
Proceedings of the Natural (2) Theory of spontaneous generation
History society of Brunn’. His (3) Theory of organic evolution
findings remained unknown
until these were rediscovered by (1) Theory of special creation
three biologists namely Hugo
Devries of Netherland, Karl This hypothesis says that all living creatures are
Correns of Germany and Erich created on the earth due to a supernatural power or God’s
Van Tshermak of Austria grace. Different religious books have mentioned it in their
independently in 1900. The work own way. However, due to the lack of proper evidence this
of Mendel was published in 1901. hypothesis has been already rejected.
Mendel’s findings formed the
basis of the science of genetics
and he is credited as the father of
genetics.

316 | Evolution

(2) Theory of spontaneous generation

This theory states that living things were originated from non-living substances
by spontaneous generation.

This theory was given by Anixamandex (611-547 B.C.) and Aristotle (384-3322
B.C.). They thought that fish and frogs originated from mud; rats came from garbage,
insects from plant sap, ants from sugar and micro-organisms from air and water
spontaneously.

Von Helmont in the 16th century did an experiment and concluded that when
wheat bran was kept with a dirty stinky and sweaty shirt for twenty one days, it
gave rise to rats. Later, this theory was rejected by some scientists like Louis Pasteur,
Francesco Redi performing various experiments.

(3) Modern concept of origin of life

This was given by Russian scientist. A.I Oparin (1923 AD) and was later
supported by his contemporary English co-worker, J.B.S. Haldane (1928 AD). It states
that life was originated from non-living substances slowly by the chemical evolution
followed by the biological evolution.

At first, macromolecules like protein, carbohydrate, fat, ammonia, etc. were
formed from the micro molecules like carbon, hydrogen, nitrogen, oxygen, etc. Then
they formed protoplasm i.e. The first living basis of life. Thus, the process of forming
living substances from non-living substances is termed as abiogenesis. Then, the cells
became more and more complex leading to the evolution.

The evidence shows that the evolution has taken place. So, this hypothesis has
been accepted to some extent.

MEMORY TIPS

Richter (1865 AD) had propounded that the first life on the earth had come from
another planet in the form of seeds, spores or pollen grains.

Evidences of evolution

The major evidences of evolution are:
i) Evidence from the study of fossils or palaeontology.
ii) Evidence from comparative morphology and anatomy. (Homologous

organs and analogous organs)
iii) Embryological evidences.
iv) Evidence from the study of vestigial organs.
v) Evidence from the geographical distribution of organisms.
vi) Evidence from the connecting links.

New Creative Science, Class 9 | 317

i) Evidence from fossils or palaeontological evidence

Fossils are the trace or the remnants of dead
plants and animals preserved on the earth’s crust.
A fossil is a relic of the past life. The study of fossils
is called paleontology. Fossils are the strongest
evidence of the evolution because scientists have
been able to trace the phylogeny of animals like
horses, camels, dogs, elephants, etc.

The fossils of simple and primitive organisms Fossil of archaeopteryx

are found on the lower strata of rocks whereas fossils of advanced and recent

organisms are found on the upper strata of the rocks. This shows that lower and

simpler organisms were originated before complex organisms. Not only this, but the

study of fossils also gives us the following information supporting evolution:

i) The organisms that existed in the past were different from the present day

forms.

ii) Some animals like dinosaurs, which have already been extinct existed in the

past.

iii) The study of fossils shows the gradual and continuous progress of organisms

from simpler to the complex forms.

iv) It also shows that new types of species appeared in one period and became

abundant in the next period, and gradually disappeared in the later periods.

ii) Evidence from comparative morphology and anatomy

When the morphological and anatomical structures of different organisms are
compared, they also give the evidence of evolution. It can be studied under the
following two headings.

(a) Homologous organs (b) Analogous organs

(a) Homologous organs

The organs in different organisms which
have the same origin and basic structure but
have different functions are called homologous
organs, e.g. forelimbs of humans, flippers of
whales, wings of birds, forelimbs of horses,
patagium of bats, etc. have the same structure
as all of them comprise of humerus, radius,
ulna, carpals, metacarpals, and phalanges.
But, they have different functions like the
flippers of whales are used to swim, the wings

318 | Evolution

of birds are used to fly and we use our hands for catching, grasping, holding, etc. The
presence of homologous organs in different organisms suggests that these animals
are evolved from the same ancestors.

(b) Analogous organs Analogous =

The organs in different organisms Insect
which have the different origin and basic
structure but have the same functions are
called analogous organs, e.g. wings of birds,
bats, insects, etc.

Thus, the study of analogous organs

tells us that insects and birds are evolved

from two different ancestral blocks. It also Pterodactyl Bird Bat

suggests that living beings modify their body structure according to the habitat and

condition where they live. Thus, it shows the mechanism of evolution.

QUESTIONS >>
# How do homologous and analogous organs support evolution?
# What is the similarity of the wings of birds, bats and insects?

iii) Evidence from embryo or embryological evidence

An embryo is a developed zygote. It is a very small and primitive structure. It is
obtained from the mitosis cell division of a zygote. It gives rise to a new young one.

When, the embryos of different organisms like fishes, amphibians, birds, reptiles
and mammals were studied, they showed many similarities in their structures. It
again shows that they have a common ancestor and thus evolution has taken place.

Fish Salamander Tortoise Chick Rabbit Human
Evidence from emgryo or embryological evidence

New Creative Science, Class 9 | 319

iv) Evidence from the geographical distribution of organisms

The earth has many geographical structures like oceans, rivers, mountains,
deserts, etc. When an organism grows in a new place with different climatic conditions
then it acquires new features in their body, which are inherited from generation to
generation, and finally this leads to origin of a entirely different species.

It suggests us that the organisms found in the similar climatic condition may be
different if they have a different origin. Also, the organisms of the same origin reach
different places with climatic diversity, they may change themselves and become
different from each other.

v) Evidence from the study of vestigial organs

The organs which are found in the body in rudimentary or functionless forms
are called vestigial organs. For example, vermiform appendix, tail vertebrae (coccyx),
nictitating membrane, the segmental muscles of the abdomen, the muscles of external
ears, hairs on human body, right lungs of snakes, halters of flies, hind limb of
python, etc.

In lower organisms, these organs are present in developed forms but they are
developed rudimentary forms in higher animals. It suggests the evolution process.

vi) Evidence from the connecting links

There were some organisms which come into existence on the earth, it serves
as a connecting group between two different groups of organisms. Such animals are
called connecting links. The study of fossils of these organisms proves this fact.
(a) Archaeopteryx is a connecting link or bridge animal between birds and reptiles.

It has wings, a beak and a body covered with feathers like those of birds but has
teeth and claws like those of reptiles.
320 | Evolution

(b) A duck billed platypus is the connecting link between mammals and birds as it
has a beak and oviparous like those of birds but has mammary glands and body
covered with fur like those of mammals.

It suggests that amphibians are evolved from pisces, birds from reptiles and
mammals from birds.

Archaeopteryx Euglena Virus

MEMORY TIPS
A duck billed platypus is a living animal which is found only in Australia.

QUESTIONS >>
# How do bridge animals support evolution?

Theories of evolution

Many theories of evolution have been put forth by different scientists at different
times supporting evolution. Among them, the popular theories of evolution are:

(1) Lamark’s theory of evolution or Lamarkism
(2) Darwin’s theory of evolution or Darwinism
(3) Theory of mutations

(1) Lamark’s theory of evolution or Lamarkism

This theory was proposed by a French biologist, Jean Baptiste
de Lamarck (1744-1829 AD). His theories are popularly known as
Lamarckism, which can be described in the following three points.

i) Direct environmental effect
ii) Use and disuse of organs
iii) Inheritance of acquired characters

i) Direct environmental effect Lamarck

According to Lamarck, environmental factors affect directly the mode of life

in an organism. Due to the change in the environmental conditions, living things

need changes for adjustment. These changes are inherited, and finally a completely

different organism is originated.

New Creative Science, Class 9 | 321

ii) Use and disuse of organs
According to Lamarck, when organs are used continuously then they become

more developed and their size increases, whereas if they are not used completely then
they slowly reduce in size and finally disappear. For example, long necked giraffe
developed from the short necked giraffe because of continuous stretching of their
neck. Similarly, snakes lost their limbs because they didn’t use it during crawling.

iii) Inheritance of acquired characters
The characters gained by living beings during their life-time are called acquired

characters, e.g. wrestlers and athletes make their body strong due to the continuous
exercises. People learning to sing, dance, swim, etc. in their lifetime are the acquired
characters. According to Lamarck, these acquired characters are transferred from
generation to generation until a completely different species is produced.

Objections of Lamarckism

Lamarckism was an incomplete theory. Later, it was criticized by many scientists.
The criticisms of Lamarckism are as follows:

(i) All acquired characters may not be inherited like the knowledge and skill of
parents. Biceps and triceps muscles of wrestlers are not inherited to the next
generation.

(ii) It is wrong that the organisms can modify their organs according to their
need.

(iii) Weismann cut the tail of rats and bred. This experiment was repeated
for more than 20 generations, but still the rats were born with tails. Thus,
Lamarck could not experimentally prove that the use and disuse of organs
can modify them.

MEMORY TIPS
Lamarck is known as the father of evolution.

322 | Evolution

QUESTIONS >>
# What are the criticisms of Lamarckism?

Darwinism

This theory was given by English naturalist, Charles Darwin in 1857 AD.
Darwinism is also called Theory of natural selection. He wrote a book Origin of
Species in 1859 AD, in which he explained the following points:

i) Enormous fertility or over production
ii) Struggle for existence
iii) Variations and heredity
iv) Natural selection
v) Origin of species

i) Enormous fertility or over production

All the living organisms have tremendous capacity to produce a large number of
offspring. This is called the Biotic potential.

A pair of housefly can produce more than 5 trillion offspring in a year. Similarly,
a slow breeding elephant can produce about 50 million offspring after 900 years. The
population increases at the geometric ratio.

ii) Struggle for existence

After coming to the earth, organisms should compete for many factors like food,
shelter, environmental conditions, etc. for their existence. The competition of food
and shelter may be intraspecific or interspecific. An intraspecific competition occurs
among the members of the same species like deer with deer, leopards with leopards
but the interspecific competition is between two different species like deer with
leopards, etc.

Not only for food, organisms must struggle with the environment and nature for
their survival.

iii) Variations and heredity

The changes occurring in living organisms are termed as variations. Some
variations are suited to the environment and others are not. The useful variations
are inherited from generation to generation. After a long interval, these variations
become their own characteristics to give rise new species.

New Creative Science, Class 9 | 323

iv) Natural selection
Nature selects the suitable species to allow them to survive. At the time of natural

selection, only these organisms survive which have favourable or suitable variation
and others die. So, it is also known as the survival of the fittest one.
v) Origin of species

In the course of variation, natural selection and inheritance, the organisms go
on becoming different from their parents continuously and ultimately a new type of
species is formed. This is called the origin of new species.

According to Darwinism, in the past there were both the long-necked giraffes
and short-necked giraffes. When there was lack of grass in the ground only the long-
necked giraffes could survive by eating the leaves of trees and the short-necked
giraffes died. Then, the long neck of a giraffe is inherited. It lead to the present day
long-necked giraffes.

MEMORY TIPS
Neo-Darwinism is formed by the combination of two different theories of the
evolution like the mutation theory and Darwinism.

Objection of Darwinism

i) It doesn’t explain how variations occur.
ii) It doesn’t explain the occurrence of vestigial organs in the body of living

organisms.
iii) Only the useful variations are not selected.
iv) Only the natural selection is not the cause of speciation but mutation may

also lead to the origin of new species.

324 | Evolution

Mutation Theory

This theory was propounded by a Dutch scientist Hugo De Vries in 1901 AD. It
states that, appearing the large number of variations suddenly and spontaneously in
the offspring is the causes of evolution.

Thus, the mutation is defined as the sudden and heritable change in the hereditary
constitution of organisms.

An organism affected by mutation is called a mutant and the causes of mutation
(like radiations and chemicals) are called mutagens. An example of mutation are six-
fingered limbs, disability of persons by birth, cut on the lip, etc.

MEMORY TIPS

Atavism is the sudden appearance of certain characters that are absent in present
forms but were present in our ancestors, e.g. presence of long hairs on the body or
face, or the presence of a small tail at the birth of a person, etc.

ANSWER WRITING SKILLS

1. Archaeopteryx is known as the connecting link between reptiles and birds. Why?
Ü Archaeopteryx has both the characters of reptiles and birds. So, it is known as the

connecting link between reptiles and birds.

Reptilian characters Bird-like characters

Presence of teeth, claws, scales on the Presence of wings, a beak and a body

body and tail vertebrae. covered with feathers.

2. Why is the vermiform appendix in a human body called a vestigial organ?
Ü The vermiform appendix in the human body is a functionless and reduced organ.

It is in the a well-developed form in herbivores. So, it is called a vestigial organ.

3. How does the evolution of the long-necked giraffe take place according to the
Lamarkism?

Ü According to the Lamarkism, the present long-necked giraffe has evolved from
the ancestral short-necked giraffes. When there was the lack of food in the ground,
the giraffes tried to survive by eating the foliage of trees by the continuous
stretching of their neck. Due to this, in the next generation, the giraffes were
produced with a long neck. This continuous use of their organ and inheritance of
the variation lead finally to the giraffes with long necks.

New Creative Science, Class 9 | 325

4. How do the homologous organs support the evolution?
Ü Homologous organs are the organs in the different organisms which have

the same basic structures and origin but different functions. For example, the
forelimbs of humans, the wings of bird, the forelimbs of horses, etc. The same
basic structure of these organs shows that the birds, humans and horses were
evolved from the common ancestors and hence this supports evolution.

5. Fossils are the strongest evidence of evolution. How?
Ü Fossils give information on the past organisms that came into existence on the

earth as the fossils are the remnants of them. New, technologies like carbon
dating and uranium dating help to know their age too. Thus, we can also find
out the time when they existed, the climatic condition of that period, etc. By
studying fossils, scientists have traced the evolutionary history of animals like
horses, dogs, cats, camels and human beings, too. So, fossils are the strongest
evidence of the evolution.

SUMMARY
” The gradual and continuous change of living organisms from simpler forms to

higher and more complex forms is called evolution.
” The hypotheses given about the origin of life on the earth are:

• Theory of special creation
• Theory of spontaneous generation
• Modern concept of origin of life
” There is ample evidence of evolution of life on the earth.
” Evidence from fossils is the strongest evidence of evolution.
” The organs having the same basic structures and origin but different functions
are called homologous organs.
” The organs having the same function but different origin and basic structure
are called analogous organs.
” Vestigial organs are the organs found in the reduced and functionless form in
our body.
” Archaeopteryx, platypus and euglena are the bridge animals.
” The theory given by Lamark is called Lamarkism.
” The theory of evolution given by Darwin is called Darwinism.
” Mutation is a sudden change in an organism due to the chromosomal disorder.

326 | Evolution

EXERCISE

1. What do you mean by organic evolution? Give the evidence which support the evolution.
2. What do you mean by Palentological evidence? How does it support evolution?
3. Describe how the homologous organs and analogous organs support evolution.
4. What are vestigial organs? Give four examples which are present in a human body.
5. What do you mean by a connecting link? Why is a platypus known as a connecting link

between mammals and birds?
6. How does embryological evidence support evolution?

7. Write short note on: (b) Natural selection
(a) Use and disuse of organs (d) Struggle for existence
(c) Survival of the fittest one

8. Write the criticism of Lamarkism and Darwinism.

9. What are mutation, mutagen and mutant? Give two examples of mutation.

A

B GLOSSARY
C

Enormous : very high

Variation : the changes found in the organisms

Micro-molecules : small molecules

Macro-molecules : large molecules

Evolution : slow and continuous change from the simpler form to the complex form

Mutation : sudden and discontinuous variation



New Creative Science, Class 9 | 327

UNIT

21 NATURE AND ENVIRONMENT

About the Scientist Introduction

Ernst Heinrich Philipp The earth is made up of soil, rocks, rivers, lakes,
August Haeckel ponds, seas, oceans, etc. The surface of the earth is covered
with a thick layer of atmosphere. All the living organisms
Ernst Heinrich Philipp are present on the earth. These living organisms fulfil their
needs from their surroundings. They get air, water, food
August Haeckel (February and shelter from the same environment. Ecology is the
science of study of organisms of their habitat in the native
16, 1834 – August 9, 1919), environment. An individual cannot survive in isolation in
nature. It should associate with both living and non-living
also written von Haeckel, components present in the nature.

was an eminent German The interaction of living (biological) and non-living
(physical) components of the environment constitute an
biologist, naturalist, ecosystem. The ecosystem may be a small as an aquarium
and as big as an ocean. The term ecosystem was first
philosopher, physician, proposed by a British ecologist A.G. Tansley in 1935 A.D.

professor and artist, who Ecosystem is a delicate and dynamic balance existing
between the living and non-living components of the
discovered, described and environment.

named thousands of The population of the same species forms the
community, and the community along with the abiotic
new species, mapped a factors constitutes an ecosystem in any place. And the
entire ecosystem taken together in an area of the same type
genealogical tree relating of climate is called a biome.

among all life forms, and Factors influencing plants and animals

coined many terms in All kinds of living organisms fulfil their needs from
their surroundings. They get air, water, food and shelter
biology, including phylum, from the same environment. These environmental factors
directly or indirectly affect living organisms. There is a
phylogeny, ecology and the close relationship between living organisms and non-
living components of the environment. It is a permanent
kingdom Protista. Haeckel cyclic process. This relationship is called ecosystem.

promoted and popularized

Charles Darwin’s work in

Germany and developed the

controversial recapitulation

theory (“ontogeny

recapitulates phylogeny”)

claiming that an individual

organism’s biological

development, or ontogeny,

parallels and summarizes its

species’ entire evolutionary

development, or phylogeny.

328 | Nature and Environment

Components of the ecosystem

The components of an ecosystem can be broadly categorized into two major
groups. They are:

(1) Abiotic components
(2) Biotic components

(1) Abiotic components

The non-living or the physical components of the ecosystem are called its abiotic
components. The physical components are:

(a) soil (b) water (c) air (d) temperature
(e) pressure (f) rainfall (g) humidity

(a) Soil

Soil is one of the chief abiotic factors which forms the surface of the earth. Plants
are the main sources of food for all living organisms and soil is the substratum of
these plants. Soil is also the habitat of many organisms.

Soil is composed of minerals, water, air and organic matters. Plants take these
materials from soil to produce their own food. All animals are dependent on these
plants directly or indirectly for their food. Soil is also the habitat of millions of
organisms. The type of soil determines the number of creatures living on it.

(b) Water

Water is the basic need of all the living creatures on the earth. So, it is also said
that water is life as no life is possible without water. From the water collected in a
small ditch to the vast ocean, water is also the habitat of millions of creatures in the
world. Thus, water is also an essential abiotic factor of the ecosystem.

(c) Air

Air is the mixture of different gases. Organisms may survive without food and
water for many days but without air or oxygen no creature can survive even for a
few minutes. Thus, oxygen is the basic need of all living organisms. Besides oxygen,
carbon dioxide of the air is used by plants for photosynthesis to prepare food for
themselves and all other creatures. So, nitrogen is used by plants to make protein.
Thus, air is the vital abiotic factor of the ecosystem.

(d) Sunlight

Solar energy is the main and ultimate source of energy of all living organisms.
The sun is the main source of heat and light not only on the earth but in all the
members of the solar system. The chlorophyll of green plants traps sunlight, which is

New Creative Science, Class 9 | 329

used by them to prepare their food. We know plants are the main sources of food for
all the living creatures. All the climatic factors depend upon sunlight. It determines
the climatic diversity, which directly influences the distribution of living creatures on
the earth.

QUESTIONS >>
# What are the chief abiotic factors of the ecosystem?
# Write the role of abiotic factors in the ecosystem.

(2) Biotic components

All the living creatures (from a unicellular microscopic organism to the gigantic
multicellular organisms) come under the biotic components of the ecosystem. On the
basis of their nutritional relationship, they can be classified into three main groups.
They are,

a) Producers b) Consumers c) Decomposers

a) Producers

Producers are the organisms which can prepare their own food by using the
various abiotic components of the ecosystem. They are also known as autotrophs.
All the green plants are the autotrophs or producers which may be phytoplanktons,
herbs, shrubs and trees. Green plants take in carbon dioxide, water and sunlight
through various processes and synthesize food or starch from them. They are the
primary sources of food for all the living creatures in the world. Plants also balance
the amount of gases in the atmosphere.

b) Consumers

The organisms which depend upon others for their food are called consumers.
They are also known as heterotrophs. Consumers are divided into the following
categories.

i) Primary consumers ii) Secondary consumers

iii) Tertiary consumers

i) Primary consumers

These are the organisms which directly feed on green plants or producers. They
are herbivores. Protozoan, crustaceans, zooplankton, etc. are the examples of the
primary consumers of an aquatic ecosystem. Similarly grasshoppers, rabbits, deers,
goats, etc. are the primary consumers of the terrestrial ecosystem.

330 | Nature and Environment

ii) Secondary consumers

These are the organisms which feed on primary consumers. They are the
carnivores. For example, dogs, cats, fox, frogs, snakes, wild cats, birds, fishes, etc.

iii) Tertiary consumers

These are the consumers which feed on the secondary and primary consumers.
They cannot be preyed upon further by other organisms. So, they are also known as
top consumers, e.g. lions, tigers, crocodiles, whales, etc.

(c) Decomposers

These are the microscopic organisms which break down complex organic
compounds into simpler compounds so that simpler compounds can be reused by
plants for synthesizing their food. These are saprophytic organisms, e.g. bacteria,
fungi and some other microbes. They help to maintain the ecosystem stable and
dynamic.

MEMORY TIPS
 Herbivores feed only on plants.
 Carnivores feed on the flesh of other animals.
 Omnivores feed on both plants and animals.
 Saprophytes feed on dead and decayed organic matters.
 Parasites feed on their hosts and also harm their hosts.

Interrelationship between the biotic and abiotic components
of the ecosystem

Producers, consumers and decomposers are the biotic components of the
ecosystem. They are interrelated with each other to form the ecosystem. The producers
use abiotic components to make or synthesize their food. Herbivores or primary
consumers feed on green plants. Similarly, carnivores feed on herbivores. When these
living components die, the complex organic matter is converted into simpler forms
and is mixed up in the soil. This process is done by decomposers. The producers again
absorb these inorganic substances for their growth and development. In this way,
there exists a very close relationship among the abiotic factors, producers, consumers
and decomposers of the ecosystem.

Autotrophic organisms

Autotrophs are the organisms which can prepare their own food by using the
various abiotic components of the ecosystem. They are also known as producers.
All green plants are called autotrophs or producers. They may be phytoplankton,
herbs, shrubs or trees. Green plants take carbon dioxide, water and sunlight through

New Creative Science, Class 9 | 331

various processes and synthesize their food. This process is called photosynthesis. The
process by which green plants convert inorganic compounds into organic compounds
is called autotropism. They are the primary sources of food for all the living creatures
in the world. Plants also balance the amount of gases in the atmosphere.

Heterotrophic organisms

Organisms that cannot produce their own food by themselves and therefore
depend upon other organisms for their food are called heterotrophic organisms.
Plants without chlorophyll in them and animals are the examples of heterotrophic
organisms. Heterotrophic organisms directly or indirectly depend upon producers
for their food. So, they are also known as consumers. Heterotrophic organisms have
different modes of nutrition. They may be parasitic, saprophytic or holozoic.

Parasitic nutrition

Organisms that completely depend upon the bodies of other living organisms
for their food are called parasites. The mode of nutrition taken by parasites is called
parasitic nutrition. The organism that is infected by parasites is called a host. The
examples of parasites are round worms, tapeworms, E. coli, Entamoeba, leeches, liver
flukes, bed bugs, lice, etc. Roundworms suck the nutrients from the intestine of the
human body.

Saprophytic nutrition

Organisms that obtain their food from dead and decayed organic matters are
called saprophytic organisms (saprophytes). The mode of nutrition of saprophytic
organisms is called saprophytic nutrition. Mushroom, molds, mucor, orchids and
certain bacteria are the examples of saprophytes.

Holozoic nutrition

Those organisms that are capable of obtaining food from different kinds of
animals and plants are called holozoic organisms. Holozoic organisms use different
kinds of organic matters in their food. They digest these foods to obtain nutrients.
The undigested product is excreted by their body. The mode of nutrition shown by
holozoic organisms is called holozoic nutrition. A large group of animals including
humans shows such types of nutrition.

Differences between autotrophs and heterotrophs

Autotrophs Heterotrophs

i) They can synthesize their own i) They depend upon autotrophs for their

food. food.

ii) They have chlorophyll. ii) They do not have chlorophyll.

Examples, all green plants. Examples, humans, cows, bear, deer,
etc.

332 | Nature and Environment

MEMORY TIPS

Mosquitoes, roundworms, tapeworms, leeches, liver flukes are the parasitic animals
and Puccinia (rust) and Ustilago (smut) are the parasitic plants.

Types of ecosystems

There are mainly two types of ecosystems. They are:

A) Terrestrial ecosystem ii) Grassland ecosystem
i) Forest ecosystem

iii) Desert ecosystem

B) Aquatic ecosystem
i) Pond ecosystem

ii) Sea and ocean ecosystem

Forest ecosystem

The ecosystem which is present in the forest is called the forest ecosystem. In the
forest ecosystem there are different abiotic and biotic components. They are given
below:

A) Abiotic components: Air, water, soil, sunlight, etc.
B) Biotic components: They are divided into following sub-groups.

i) Producers: Grass, bushes, trees, etc.
ii) Primary consumers: Deer, ghorals, zebras, etc.
iii) Secondary consumers: Jackals, foxes, etc.
iv) Tertiary consumers: Lions, tigers, etc.
Decomposers: Micro-organisms like, bacteria, fungi, molds, etc.

Pond ecosystem

New Creative Science, Class 9 | 333

The ecosystem which is present in the

pond is called the pond ecosystem. In the

pond ecosystem there are different abiotic

and biotic components. They are given

below:

A) Abiotic components: Air, water, soil,

sunlight, etc.

B) Biotic components: They are

divided into following sub-groups.

i) Producers: Hydrilla, algae,

phytoplankton, etc.

ii) Primary consumers: Small fish, tadpoles, dragonflies, larvae of mosquitoes,

zooplankton, etc.

iii) Secondary consumers: Frogs, big fishes, etc.

Decomposers: Micro-organisms like, bacteria, fungi, molds, etc.

Energy circulation in an ecosystem

The energy circulates in an ecosystem in the form of food which is unidirectional.
The solar energy is the main source of energy in an ecosystem. It is used by green
plants. The food prepared by green plants is circulated through primary consumers,
secondary consumers, tertiary consumers, decomposers and finally to the soil. In this
process, food chain and food web are formed.

Food chain

The transfer of energy and
food from one trophic level to
another level of an ecosystem
by the process of eating and
being eaten is known as food
chain.

Green plants or producers
are the first trophic level, which
are eaten by the second trophic
level or herbivores. They are
again eaten by secondary
consumers and the secondary
consumers are eaten by tertiary
consumers. Finally, when the
entire organisms die, they are

334 | Nature and Environment

converted into simpler organic matter by decomposers. In this way, all the organisms
in an ecosystem are linked by a sort of food chain.

The arrangement of producers and consumers in an ecosystem is called trophic
structure and the position occupied by an organism in a food chain is called level.

Types of food chain

There are mainly three types of food chain. They are:
1) Grazing food chain
2) Detritus food chain
3) Parasitic food chain

1) Grazing food chain

In this food chain, green plants or producers are the first trophic level. The
herbivores feeding on producers form the second trophic level and carnivores are the
third trophic level i.e.

Producers → Herbivores → Carnivores

First trophic level Second trophic Third trophic level

Grass Deer Tiger

2) Detritus food chain

In this food chain, dead and decayed organic matters are the first trophic level.
The primary consumers are detritivores which include protozoan, bacteria, fungi,
etc. The detritivores are eaten by secondary consumers which include insects, larvae,
nematodes, etc. This food chain is shorter than the grazing food chain.

3) Parasitic food chain

In this food chain, the food transfers from hosts to parasites.

i.e. Hosts → Parasites
Second trophic level
First trophic level

QUESTIONS >>
# What do you mean by food chain? What are its types?

New Creative Science, Class 9 | 335

Food Web

In an ecosystem, it is not
always the case that plants
should be eaten always by
rabbits or grasshoppers.
Instead, grass can also be eaten
by deer or zebras. Similarly,
grasshoppers should not
always be eaten by snakes. It
can also be eaten by the frog.
Thus, we can say that the
trophic relationship between
organisms is not always in
a simple chain but forms a
complicated network.

The network of food chains interconnected with various trophic levels is called a
food web. The food web provides the alternative pathways of food availability.

Basic requirements of human beings

When we say about the basic needs of human beings, it is always food, cloth and
shelter.

(1) Food: Food is the most vital requirement for plants and animals. Human
beings cultivate different cereals, fruits, vegetables and rare animals for the
consumption of their food. Since, the time immemorial, human beings have been
using different types of sea and land animals for their food.

(2) Shelter: Human beings build houses and buildings for their own shelter. The
raw materials of construction come from the environment. The woods, cement,
concrete, stones, etc. are all derived from the environment directly or indirectly.

(3) Cloth: To protect the body from the extreme climatic condition and other injuries,
we should wear clothes. The raw materials for making clothes also come from
the nature. Cotton seeds, silkworm, leather-like raw materials come from the
environment.

Effects of Climate Change

Climate is the average weather in a place over many years. The weather can
change in just a few hours. Climate takes hundreds, thousands, even millions
of years to change. Due to various human activities there occurs mixing of excess
greenhouse gases like carbon dioxide, methane, nitrogen oxides, sulphur oxides, etc.

336 | Nature and Environment

in the atmosphere. It causes climate change. Human beings are mainly responsible to
accelerate climate change. Thus, climate change is simply a long-term change in the
average atmospheric condition of a place. Climate change causes significant effects to
humans, animals and the environment.

a) Effects on human health

The first major health impact of climate
change is the rise in the rate of diseases and
mortality. The increasing rate of mortality is
due to floods, droughts, tsunamis, heat-waves
and other disasters. They kill thousands of
people in both developed and developing
countries. High temperature induces major
health risk to older people and children. Many
fatal diseases, including malaria, jaundice,
hepatitis, cholera, etc. are more violent in high
temperature.

b) Effects on agriculture

Agriculture is one of the major sectors which is affected by climate change. It is
directly dependent on the temperature and precipitation. Change is precipitation and
temperature directly affects the agricultural practices and food production. Erratic
and unpredictable heat waves and cold waves also affect crops. Change in climate
of a place also changes the frequency of the occurrence and the types of pests and
diseases that affects crops. Change in atmospheric carbon dioxide and ground-level
ozone concentration changes in the nutritional quality of some foods. The increase
in sea level also decreases agricultural land areas. Due to change in temperature and
precipitation, there is change in availability of water. Wetter areas become drier,
and drier areas become wetter. The problem of droughts will rise. It decreases crop
production. There will be a problem of irrigation, which also affects the crop yielding.

c) Effects on water resources

The water resources sector is also a susceptible sector with regard to the effect
of climate change. Climate change results in high and erratic rainfall trends in
future. This causes less infiltration of water into the ground and high surface run-
off. This increases the amount of water in rivers but only for a short duration. The
ground water becomes scarce and water scarcity is likely to occur in the near future.
Apart from this, increase in temperature increases the rate of meting of glaciers and
mountains ice caps. This finally melts all the snow from our mountains and depletes
all water resources. It finally can cause the disappearance of snow-fed streams and
rivers. Many streams, springs, lakes and ponds of Nepal have already dried up. This
can cause the scarcity of water for drinking, domestic use, irrigation and hydropower
production.

New Creative Science, Class 9 | 337

d) Effects on human habitation

Climate change has started to displace people from one area to another. The
people on the seashore areas are at high risk of different climatic hazards including
tsunami. People from the mountainous regions and in downstream of the glaciers are
also at risk of Glacial Lake Outburst Flood (GLOF). Many islands and lands lying just
above the sea level can disappear in the near future if the rate of sea level rising due to
climate change goes like this many people from many hilly parts of Nepal have been
displaced to other areas due to drying up of water sources like springs and streams.

e) Effects on infrastructure

Due to climate change, rising sea level, flowing storm, heavy rainfall, etc.
take place. They increase damage to infrastructure including roads, buildings and
industrial facilities. Flooding along rivers, lakes due to heavy monsoons, prolonged
rains, and rapid melting of snowpack is exceeding the limits of flood protection
infrastructure designed for historical conditions. Extreme heat is damaging
transportation infrastructure such as roads, rail lines, airport runways, etc. Power
plants, roads, bridges, etc. are damaged during these extreme events. Our historical
and architectural heritages like temples, monuments, museums, etc. get damaged
due to unpredicted events like landslides, rainfalls, floods, etc.

f) Increase in global temperature

Scientists are convinced that our globe
is warming day to day. The earth’s average
temperature has risen by about 0.8°C (1.4°F)
over the past 100 years. The earth is warming
but all the places are not heating up at the
same rate. The Arctic region is warming
more than other regions. The land areas are
warming more than ocean areas. But a few
places are actually cooling. In the case of
Nepal, a study shows that the average temperature of Nepal has increased from 0.6
to 0.980°C over the last 30 years. Another study shows that under the same condition,
the temperature of Nepal will increase to 1.4 0°C in 2030 and 1.70°C in 2050.

g) Effect in biodiversity and ecosystem

Biodiversity means the variability in living forms of the earth. Our earth contains
diverse groups of organisms from terrestrial ecosystems, freshwater ecosystems and
marine ecosystems. A study shows that increase in global warming means increase
in temperature. Increase in temperature around 4°C by 2100 AD would lead to the

338 | Nature and Environment

major extinctions of the terrestrial vegetation. With very high confidence, the study
shows that warming of 2°C above 1990 would also result in mass mortality of coral
reefs globally. Except the loss of biodiversity, plants and animals are also expected
to adapt to the changing environment by changing their habit and life cycles. These
adaptations may affect the interactions between living things and their habitats.

Ecosystem services

The services that are provided by ecosystem are called ecosystem services. A
brief description of the services provided by the ecosystem is mentioned below.

1. Provisioning Services

The services provided by ecosystem in the form of supply of ecosystem products
are called provisioning services. The major provisional services of ecosystem are:

i) Food and fiber: Plants and animals from ecosystem are the sources of food
for humans. They also provide fibres for humans in the form of silk, cotton,
jute, feathers, wool, leathers, etc.

ii) Fresh water: A healthy ecosystem yields fresh water for humans.

iii) Fuel: Ecosystem provides us fuel in the form of firewood, dried organic
matters, dungs, etc. Hydropower and other biomass energy come from a
healthy ecosystem.

iv) Medicinal and genetic resources: Ecosystem provides plants and animals
high medicinal value for humans. Apart from them, ecosystem is the pool of
a wide variety of genetic resources for the utilization of humans.

2. Regulating Services

The services provided by the regular functioning of the ecosystem process are
called regulating services. Some of the important regulating services are:

i) Climate regulation: Ecosystem process like photosynthesis and transpiration
from plants and respiration from plants and animals check the amount of
concentration of carbon dioxide and water in the atmosphere. This regulates
the temperature and precipitation locally.

ii) Water purification: Different plant species absorb nutrients and toxic
materials from water. Also, plants retain the moisture in the soil and help
natural infiltration and percolation.

iii) Pest and disease control: The natural process of maintaining stability in the
ecosystem also controls pests and disease causing organisms. This causes
humans and their crops less risk to various kinds of diseases.

iv) Landslide and erosion control: Grasslands and the lands covered with
plants are at less risk to erosion. Similarly, plants also check landslides.

New Creative Science, Class 9 | 339

3. Cultural services and recreational services

The service provided by ecosystem as non-material benefits for people is called
cultural service. It includes spiritual enrichment, cognitive development, reflection,
recreation, and aesthetic experiences. Dense and dark forest, pure water bodies,
wild flora and faunas are considered to be of religious importance in many cultures.
Ecosystems and water bodies are the natural heritages and are the sources for
ecotourism and recreational activities. They are also the centers for education and
research.

4. Supporting services

Those ecosystem services that are necessary for the production of all other
ecosystem services are called supporting services. These include services such as
nutrient recycling, primary production and soil formation. These services make it
possible for the ecosystems to provide services such as food supply, flood regulation
and water purification. These services help the ecosystem to live as a single entity
supporting innumerous entities in it.

Ecosystem services

Provisional Regulating services Cultural services Supporting
services services
Climate regulation Spiritual and
Food Water regulation religious Nutrient cycling
Fresh water Water purification Recreation Evolution
Fibres Pests and diseases Aesthetic Soil formation
Fuels control Ecotourism Spatial structure
Biochemicals Pollination Educational Primary
Genetic resources Landslide and Inspirational production
erosion control Sense of place
Flood control Cultural heritage

ANSWER WRITING SKILLS
1. Why are plants called producers?
Ü Plants are called producers because they can synthesize their own food by using

the raw materials from the environment like air, water and sunlight.

2. Why is a cow called a heterotroph?
Ü A cow cannot prepare its own food and depends upon producers for its food. So,

a cow is a heterotroph.

3. Why is a mushroom called a saprophyte?
Ü A mushroom feeds upon dead and decayed organic matters. So, it is called a

saprophyte.

340 | Nature and Environment

4. What is detritus food chain?
Ü In detritus food chain, dead and decayed organic matters are the first trophic

level. The primary consumers are detritivores, which include protozoan, bacteria,
fungi, etc. The detritivores are eaten by secondary consumers, which include
insects, larvae, nematodes, etc.

SUMMARY

” Ecosystem is a delicate and dynamic balance existing between the living and
non-living components of the environment.

” An ecosystem contains two factors. They are abiotic factors and biotic factors.
” Abiotic factors are the non-living components of the environment such as air,

water, sunlight soil, etc.
” The biotic factors of the ecosystem include producers, consumers and

decomposers.
” Producers are the green plants which can synthesize their food by using the

abiotic components of the ecosystem.
” Consumers are the organisms which feed on producers directly or indirectly.
” Decomposers are the micro-organisms which change the complex food

materials into simpler forms.
” Consumers are of three types viz. primary consumers, secondary consumers

and tertiary consumers.
” Food chain is the transfer of energy in the form of food from one trophic level

to another.
” Food chain is of three types:

• Grazing food chain
• Saprophytic food chain
• Parasitic food chain
” A food web is the network of various interconnected food chains.
” Climate is the average weather in a place over many years.
” Climate change is simply a long-term change in the average atmospheric
condition of a place.
” Biodiversity means the variability in living forms of the earth.
” The services that are provided by ecosystem are called ecosystem services.
” The services provided by ecosystem in the form of supply of ecosystem
products are called provisioning services.
” The service provided by the regular functioning of the ecosystem process are
called regulating services.

New Creative Science, Class 9 | 341

EXERCISE

1. What do you mean by ecosystem?

2. What are the components of ecosystem? Name them.

3. What are the roles of abiotic factors in an ecosystem. Explain abiotic factors in short.

4. What do you mean by producers? Why are producers called autotrophs?
5. What are consumers? Give three examples.

6. What do you mean by decomposers? What is their role in an ecosystem?

7. Define food chain. What are the types of food chain?

8. What do you mean by food web?

9. Differentiate between:
(a) Autotrophs and heterotrophs
(b) Producers and consumers
(c) Food chain and food web

10. What will happen if all the decomposers of the ecosystem are destroyed?

11. Define autotrophic organisms, heterotrophic organisms, parasites, saprophytes and
holozoic.

12. What are ecosystem services? Write ecosystem services in points.
13. What is climate change? Describe climate change in brief.

A

B GLOSSARY
C

Parasite: which absorbs or sucks food from others

Saprophyte: which depend upon dead matter for their food

Detritus: dead and decayed organic matter

Ecology: study of the environment

Photosynthesis: the process of making food by the green plants

Food chain: the transfer of food in di erent tropic level

Food web: the interlinked food chains



342 | Nature and Environment

UNIT

22 NATURAL HAZARDS

About the Natural Introduction
Disaster
The earth is our common home. It gives us food,
In the mid-night around 3 shelter and fulfils our different needs. Different kinds of
o' clock in 2071 Shravan positive and negative incidents occur in the earth. Among
16 a fearful landslide them, some of the natural incidents balance the nature
occurred in Mankha, Jure whereas some of them create an imbalance. Thus, those
of Sindhupalchok district. natural incidents which cause destruction to lives and
It closed the flowing of property are called natural hazards. Natural hazards are
the Sunkoshi river. In also called natural disasters. Example, floods, landslides,
this disaster, around 100 earthquakes, volcanic eruptions, cyclones, etc.
people died, more than two
dozen people were lost and In the different parts of the earth, natural hazards
39 people were injured. occur in different time. In Nepal, we are suffering from
Around 11 districts were different types of hazards at different time. For example,
affected. the massive earthquake of 2072 BS caused huge loss of
life and property. The landslide of Jure in Sindhuplachok
district in 2071 BS, the flood in the terai region, etc. are
some of the natural disasters which occurred recently.

In this unit, we will discuss about natural hazards,
their effects and methods to control and their management.

Hazards

Those incidents which cause destruction to lives and
property are called hazards. There is probability of different
types of hazards in nature. Some of them are less dangerous
and some are more. Earthquakes, volcanic eruptions,
landslide, floods, cyclones, etc. are more dangerous. They
cause loss to lives and property. These natural events
occur naturally but we human beings are also responsible
to promote them. For example, deforestation, unplanned
urbanization, unscientific research, etc. promote some of
the disasters. We cannot completely control the natural
disasters but we can minimize their risk. Similarly, we can
be prepared for such natural disasters which may prevent

New Creative Science, Class 9 | 343

us from huge loss of lives and property. Hazards can be divided into two types. They
are natural hazards and man-made hazards.

Natural Hazards
Those incidents which occur randomly by nature itself and cause huge destruction

of lives and property are called natural hazards. For example, floods, landslides,
earthquakes, volcanic eruptions, cyclones, etc.

Management of natural hazards
To manage natural hazards the following methods can be applied.
i) People should be aware about natural disasters. They should be informed
by different medias like the radio, television, newspapers, etc.
ii) After disasters, the rescue operation should be carried out immediately after
the disasters.
iii) The government should operate all the national forces to rescue the victims
and to save the property.
iv) Sanitation awareness program should be launched in disaster areas and
people should be migrated to safe places.
v) To minimize some natural disasters like floods, landslides, etc. and
afforestation programs should be carried out in the bare land.
vi) Well-planned urbanization may reduce the risk of danger.

Man-made Hazards
Some hazards do not occur naturally but

human beings are responsible. Such hazards
are called man-made hazards. Such hazards are
occurring due to human activities against the
nature. For example, road accidents, epidemics,
droughts, nuclear radiations, chemical effects, etc.

We cannot stop natural hazards completely
but we can minimize their effects to some extent.
We can be prepared for such natural hazards. If
we become pre-prepared for such disasters we can
minimize the loss of life and property. If essential steps are taken immediately after
disasters many lives can be saved.

344 | Natural Hazards

Management of man-made hazards
i) There should be age bar for a driving licence.
ii) The government should be aware about the effects of nuclear energy
power plant.
iii) Sanitation programs should be carried out in communities.
iv) Afforestation programs should be carried out in the bare land.
v) Local television and radio should be mobilized for awareness programs.
vi) Earthing should be done in the home.

Preparedness of disasters

The following methods can be applied to be prepared for disasters.

We can anticipate disasters, its effects and preparedness. There should be
sufficient storage of disaster relief materials and well managed communication
systems.

Methods to minimize the effects of disasters

i) Helping each other during and after the disasters.
ii) Rescue operations should be carried out immediately after the disaster.
iii) Well-trained manpower should be mobilized for rescue operation.
iv) Clean drinking water, dry and fast food should be distributed in the affected area.
v) Temporary shelter, cloths, temporary toilets, etc. should be managed

immediately for the victims.
vi) Essential primary health service should be provided immediately to the

victims.
vii) Different types of disaster relief programs should be lunched in the

affected area.

Glacier flood

Nepal is a Himalayan country.
We have many high mountains. In the
Himalayan region, a huge amount of snow is
accumulated. Due to the rise in temperature,
the snow slowly starts melting. Due to the
melting of snow, the glacier lakes are formed.
In our country, we have many glacier lakes.
Some glacier lakes are ready to burst and
some are in danger of bursting. Due to the
outburst of glacier lakes there will be huge
damage to life and property. Thus, the overflow of water due to the glacier outburst
is called a glacier flood. In our country, some rivers are originated from the Himalaya

New Creative Science, Class 9 | 345

region. For example, Sunkoshi, Dudhkoshi, Trishuhli, etc. We have been suffering
from glacier floods in such rivers. Our country is a Himalayan country. So, we have
always danger of glacier floods and glacier lake outbursts.

Causes of glacier floods
i) Climatic change due to pollution
ii) Increase in the earth’s temperature
iii) Earthquake
iv) Due to human activities
v) Global warming

Effects of glacier floods
i) Flood occurs in rivers.
ii) Due to the flood in snow fed rivers, it may cause loss of life and property.
iii) Natural and cultural heritages may be damaged.
iv) Loss of agricultural land and crops.

Some controlling measures of glacier floods
i) The government should study the current situation of glacier lakes.
ii) People should be aware about the environment and climatic change.
iii) Precautions should be taken if some glacier lakes are about to burst.
iv) If some glacier lakes are about to burst, the human settlement area near the
lake should be evacuated.
v) Proper education should be given to the concerned people about glacier
lake outbursts and glacier floods.
vi) After glacier floods, the affected people should be rescued as soon as
possible.
vii) The victims should be provided with essential food, temporary shelter,
clothes, medical health care, etc. as soon as possible.

Glacier lake outbursts

Nepal is a Himalayan country. We have
many glacier lakes. The lakes which are found
in the Himalayan region are called Glacier
lakes. Glacier lakes occur both in solid and
liquid states. Some have frozen ice and some
have snow. Due to the global warming, the
temperature near the areas of glacier lakes has
been increasing day by day. There is danger
of outburst of such lakes due to the increasing
earth’s temperature and climatic change. Thus, the overflow of water from the glacier

346 | Natural Hazards