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SUBHAS PUBLISHING HOUSE, BANGALORE
GOVERNMENT OF KARNATAKA
Directorate of Text Books
SC0ENCE
PART II
REPRINT
2000
EIGHTH STANDARD
SUBHAS PUBLISHING HOUSE
No. 116, 5th Main, 6th Cross, (Near Ram Mandir Bus Stop)
Chamarajpet, Bangalore - 560 018.
VIII STD TEXT BOOK PREPARATION COMMITTEE
1.
Dr. K. N. Tantry.
Rtd Reader. R.C.E
Mysore
Chairman.
Dr. C. K. Chandrasekhar
Asst. Professor of Psychiatry
NIMHANS, Bangalore - 29
Member
Dr. C Madhukar
Rtd. Principal, R. V. Teachers Collage
Bangalore
Member
Sri A. B. Katti
Asst. Master. Sheshadripuram H. S.
Bangalore
Member
5.
Sri V. Ramalingaiah
Asst. Master, Govt. P. U. College for Girls
Channapatna
Member
6.
Sri C. G. Nagaraj
Head Master. D. M. High Scool, Mysore-6
7.
Sri R. Bheema Rao
Lecturer, Govt. P. U. College, Bellary
Scrutinizer
8.
Sri H. N. Raja Rao
Head Master, Gnanamitra High School,
Bank Colony Bangalore.
Scrutinizer
9.
Sri M. H. Kavishetty, Bijapur
Artist
10.
Sri H. N. Chitragar, Raichur
Artist
11.
Sri A. N. Shashidhar
Translator
12.
Sri M. N. Suresh Asst. Master
Acharya pata shala Boys High School
N. R. Colony Bangalore
Editor
13.
B. S. Nagesha Rao
Asst. Director (Text Books)
Co-ordinator
2.
3.
4.
FOREWORD
This text book is prepared as per the syllabus
framed based on National Policy on Education 1986.
The Core Elements and Human values that are
stressed in the National Policy on Education are
addressed at length in developing lessons.
The Directorate is grateful to all those who have
participated in the production of this book.
The Text Books are reprinted after editing and
making necessary corrections. The Directorate
welcomes suggestions for further improvement of the
book.
Bangalore.
Dated 22-2-2000
(M. Jalaja Bai)
Director
Directorate of Text .Books
Bangalore - 4.
1. Title
: Science -Part ll-VIII Std.
2. Copyright holder
: Director
Directorate of Text Books,
DSERT, B.P.Wadia Road,
Basavanagidi,
Bangalore - 560 004.
3. Edited Version
: 1997
4. Reprint
: 2000
5. Publisher
: Subhash Publishing House
No. 116, 5th Main, 6th Cross,
(Near Ram Mandir Bus Stop)
Chamarajpet,
Bangalore - 560 018
6. Printing papei used
: 60 gsm, M.P.M. Paper
7. Number of copies printed : 80,000
8. Price of the Text Book
: Rs. 3.55
9. Typeset by
: Laser Line Graphics
Lalbagh Rd, Bangalore - 560 027.
: Soundari Printers
Srirampuram, Bangalore-21.
9. Printed at
Contents
CHAPTERS
Pg. No.
1.
The world of Micro-Organisms
1
2.
Adaptation and Organic Evolution
30
3.
Useful Animals and Plants
43
4.
Conservation of Natural Resources
49
Chapter 1
THE WORLD OF MICRO-ORGANISMS
There are hundreds of varieties of living organisms
around us in our world. The shapes and sizes of these
organisms are different. Some are larger in size than human
beings and some others are much smaller. Some cannot be seen
by the human eye. The size of these small organisrhs is one
micron or even less. [1/1000 th part of a millimeter is called one
micron]. Hence such small organisms are called "microbes" or
"micro-organisms". You will find it surprising to know that
these organisms live in the soil, in water, in air, on the objects
that we use, on our body and even inside our body.
Activity 1:1 Take water in a beaker and put a few pieces of hay
into it. Expose it to air. Observe it after four days. You will not find
any living thing in the beaker if you see by your naked eye. Put a
drop of the water front the beaker on a slide and cover it by a cover
slip [Take care that air bubbles are avoided]. Observe the slide
through a microscope in your school. What do you see?
Or
Take a drop oj water on a slide and allow it to dry. Add five drops of
gentian violet. Dry it again. Add a drop of cedar wood oil or liquid
paraffin oil on the dried, coloured water drop. Observe the drop
through the oil immersion objective of microscope. What do you see?
The microbes that are visible to us in a microscope are
magnified several times. They live around us in all parts of our
planet. They can exist in very hot or cold climatic conditions.
Some microbes are helpful to us. For example, it is with the
assistance of microbes that milk turns into curds; wet ground
paste of idly and dosa get fermented and bread becomes soft.
The antibiotics or vaccines that protect us against infectious
diseases, are also gifts of these helpful microbes.
But not all microbes are helpful. Some microbes produce
fatal diseases, like tuberculosis, leprosy, cholera, typhoid,
dysentery, brain fever (meningitis) or flu (influenza) and so
1
Different types of Microbes:
There are different kinds of micro-organisms. They are:
Viruses, bacteria, unicellular organisms and some algae.
Of these, bacteria and algae are the oldest organisms on earth.
They have high capability to adjust to any environment. These
were the first organisms to live on land.
Viruses:
These are the smallest organisms. Their size varies from
0.01 to 0.3 microns. They have simple structure. They have
nucleic acid surrounded by a thin film of protein. They cannot
live independently. They can live and grow inside living cells.
Figure 1.2 Virus
The main characteristic of a virus is to enter a living cell,
make use of its complete mechanism for its survival and
reproduction. Viruses replicate rapidly and multiply within a
very short time. Viruses are the cause of many infectious
diseases such as common cold, small pox, Measles, Polio and
Meningitis (brain fever) and AIDS which trouble human
beings.
Algae:
They are found in lakes, rivers, oceans or at places which
are wet and moist. The largest proportion of photosynthetic
4
activity around the world is due to algae. This activity of the
algae facilitates reduction of the carbon dioxide content and
increase the oxygen content in the atmosphere. Algae consumed
as food by fish and other aquatic animals. There are different
kinds of algae:
blue green algae, brown and red algae, green algae, and
diatoms.
Figure 1.3 SPIROGYRA - An alga
Fungi:
Fungi grow on dead and decaying plants or animal matter.
Many of them do not have the ability to move. They obtain food
from plants or animals on which they grow and branch out to
further growth. Their spores are carried and spread by the wind
and are found deposited on edible food-stuffs, on leather goods
and also on uncleaned human body. Penicillin, the much useful
5
antibiotic, is a gift of the fungus. Yeast is another fungus which
is useful in the manufacture of alcohol. There are many fungi
which can cause diseases.
Figure 1.4 bread mold
(Rhizopus)
Figure 1.5 Yeast
(Saccharomyces)
Bacteria:
The size of bacteria varies from 0.4 to 1.5 microns. They are
of different shapes:
Round, rodlike and spiral. Sometimes, bacteria are found
clinging to one another. Many of them, can move by themselves,
and many are parasites. They live and propagate in different
parts of human and animal bodies.
Figure 1.6 Different kinds of bacteria
6
Bacteria are responsible for many serious and not so
serious diseases. For example: sore throat, sepsis (of wounds),
pneumonia,
cholera,
tuberculosis,
leprosy,
sexually
transmitted diseases, dysentery etc.
Unicellular organisms: (Protozoa).
Protozoa are the biggest in size among micro-organisms.
Their size varies from 2 to 100 microns. They are the most
primitive from of life.
Some of them live on dead animals and plants. But a
majority of them are parasites, living in different parts of
plants and animals. They inflict several diseases like malaria
and amoebic dysentery to human beings.
Activity 1:3 Visit a health centre or a hospital or a clinic near
your house. With the permission of the doctor talk to the patients and
find out about their sickness. Ascertain from the doctor, who among
the patients, got diseases caused by bacteria, viruses, fungi or
protozoa. Prepare a list of the diseases and micro-organisms
responsible for them. Find out what the doctor does to keep the
disease under check or to destroy the disease causing organisms.
Likewise go to a veterinary hospital at your place. Find out and list
the diseases which are inflicted by micro-organisams in animals.
Paramecium
Entamoeba
Euglena
Trypanasoma
Figure 1.7 Unicellular organisms
7
- AvVhen a healthy person uses this contaminated
^^•et infected by the micro-organisms easily. In this
=3us diseases spread like wildfire killing hundreds
stretch.
is a very dangerous disease because, when
we patient passes watery stools and vomits
^=tind uncontrolably. Within a few hours the patient
Ihydrated and dies.
leaded typhoid is also a water borne-disease caused
—eellatyphae. These microbes reach the intestine and
=mds and then they spread all over the body. In about
S; after infection, fever develops.
zmer dreaded disease causing microbe is Entamoeba
su (a protozoan) which causes amoebic dysentery.
■otozoa attack the intestine, causing wounds which
■into ulcers and produce loose motions. There will be
clhese microbes in the faeces. A patient suffering from
;:ase may discharge 5 crores of cysts in the excreta
. single day.
can protect ourselves from water borne microbes by
»ure water and also by remembering the following
■ should not drink the contaminated water from lakes,
nds, wells, streams or rivers. - We must boil and cool
it water before we drink.
: must prefer borewell or tap water if available, to drink
to cook food.
2 must wash raw vegetables and fruits before
nsuming them.
e must not drink water from a river, lake or pond which
found to be contaminated, even on religious grounds.
e must seek advice from a doctor regarding nursing and
re of patients suffering from cholera, typhoid and
'sentery.
le following precautions must be taken in order to
it contamination of nearby water sources by microbes.
9
Transmission of microbes from one to another
The disease causing microbes are parasites. In order to
live, grow and multiply, they need a host (an animal or a
human body or any organism). Microbes cannot move very far
by themselves. To move from one body to another, they use
media like, wind, water and soil. They use even animals and
human beings to get transported.
Transmission through wind:
Remember when you or your relative in your house had a
common cold. Cough and sneezing are common symptoms
when somebody suffers from cold. When he coughs or
sneezes, millions of infecting microbes are thrown out into the
wind. When this contaminated wind is inhaled by somebody
else, then that person also catches cold. Now, this is how if one
in the family catches flu, then the others and neighbours also
catch flu.
Similarly, when a patient suffering from pulmonary or
lung tuberculosis, coughs or spits, millions of microbes enter
the air. When the contaminated air is inhaled by healthy
people, they may also get infected. This illustrates as to why it
is necessary to cover your mouth with a handkerchief while
coughing or sneezing if you are suffering from cold; flu, or
tuberculosis. The towel or handkerchief used in cleaning your
nose and mouth, must be dipped in boiling’water, washed and
dried in sunlight.
Transmission through water:
The microbes spread more efficiently through water than by
air and infect thousands of people, for example, the microbes of
cholera, dysentery, and typhoid spread through water.
Microbes which cause cholera can live in stagnant water
for 5 to 10 days. The area on both the banks of the rivers,
Ganga, Brahmaputra, Yamuna, Cauvery etc are cholera-prone.
The micro-organisms which are living in affected persons
pollute the river water when they bathe, wash, urinate in the
8
river water. When a healthy person uses this contaminated
water, they get infected by the micro-organisms easily. In this
way, dangerous diseases spread like wildfire killing hundreds
of people at a stretch.
Cholera is a very dangerous disease because, when
infected, the patient passes watery stools and vomits
repeatedly and uncontrolably. Within a few hours the patient
becomes dehydrated and dies.
The dreaded typhoid is also a water borne-disease caused
by Salmonellatyphae. These microbes reach the intestine and
lymph glands and then they spread all over the body. In about
7 or 8 days after infection, fever develops.
Another dreaded disease causing microbe is Entamoeba
histolytica (a protozoan) which causes amoebic dysentery.
These protozoa attack the intestine, causing wounds which
develop into ulcers and produce loose motions. There will be
cysts of these microbes in the faeces. A patient suffering from
this disease may discharge 5 crores of cysts in the excreta
during a single day.
We can protect ourselves from water borne microbes by
using pure water and also by remembering the following
points.
1. We should not drink the contaminated water from lakes,
ponds, wells, streams or rivers. - We must boil and cool
that water before we drink.
2. We must prefer borewell or tap water if available, to drink
or to cook food.
3. We must wash raw vegetables and fruits before
consuming them.
4. We must not drink water from a river, lake or pond which
is found to be contaminated, even on religious grounds.
5. We must seek advice from a doctor regarding nursing and
care of patients suffering from cholera, typhoid and
dysentery.
The following precautions must be taken in order to
prevent contamination of nearby water sources by microbes.
9
Defecating near the water sources (well, pond or river)
should be avoided.
2. One must build hygienic lavatories for this purpose. If this
is not possible sanitary pits can be dug.
These pits should be covered with fresh soil after use.
3. One should not wash soiled clothes in ponds, streams or
rivers.
4. We must ensure that sewage or contaminated water does
not mix with wells, river, stream or pond etc.
Activity 1:4 Make a list of additional measures by which
pollution of our water resources can be prevented?
1.
Transmission through soil:
Tetanus is a fatal disease caused by the microbe
"Clostridium tetani". A person affected by tetanus will first feel
that it is difficult fo open his jaws. It is because of the stiffening
of muscles. The stiffening of muscles spreads to the face, neck
and throat. Swallowing becomes difficult. With the spread of
the disease, the body bends like a bow and the person dies.
These bacteria live in the intestine of the herbivorous animals.
Spores of these bacteria get into the soil through faeces dropped
by these animals. Then, they enter the human body through
cuts or wounds. By understanding this mode of transmission,
steps can be taken to prevent the spread of the disease by the
following measures.
1. If you get injured by a fall or an accident or when
wounded by a sharp blade or knife, first wash the wound
with clean water thoroughly and ensure that the soil or
dust particles are removed.
2. Ensure that dirt, dust or cowdung does not come in
contact with the wound. Do not wipe the wound with the
dirty cloth.
3. Do not use rusted blades, knives or other material left
unused for a long time.
4. Seek doctor's advice. Get vaccinated against tetanus and
act as per his advice.
10
Transmission through insects:
Mosquitoes, flies, bed bugs, cockroaches and fleas are the
common carriers of disease causing microbes or germs The
microbes stick to the legs of flies or cockroaches while they
feed or walk over dirt or faeces. When such insects sit or walk
over or come into contact with the food that we eat, the germs
contaminate them and gain entry into our body.
The wounds caused by injuries get infected and will be
filled with pus. Insects like flies which are carriers of microbes
are the cause of health hazards like vomiting, loose motion,
pus formation in wounds (sepsis), worms in the intestine etc.
Biting insects like mosquitoes, bed bugs and fleas, bite a
sick person first, and pass on this infection to a healthy person
next, when they bite him to suck blood.
The mosquito and malaria:
Malaria is caused by a protozoan called 'Plasmodium'.
They gain entry to the human blood stream through the bite of
female Anopheles mosquito. They reach the liver and multiply
in its cells. They destroy and break open these cells in great
numbers and attack red blood corpuscles in the blood and gain
entry into them.
They grow, multiply and destroy the red blood corpuscles.
Forming male and female Gametocytes, they travel in the
blood stream to cause shivering and fever in victims. These are
symptoms of malaria.
When the female Anopheles mosquito sucks the blood of a
malaria patient to feed, these male and female gametocytes
reach its stomach. Here they unite and reproduce. These young
ones so formed reach the salivary glands of the mosquito. At
this stage, if the mosquito bites a healthy person, young ones
enter into the human body and the life cycle is repeated. Thus,
the protozoa causing malaria reproduce or multiply asexually
in the human body. .
They reproduce sexually in the mosquitoes. Thus in
11
malaria control, it is very important to destroy the mosquitoes
which are the carries of the causative agent. As stagnant water
is necessary for the growth of mosquitoes, care must be
exercised to see that water is not allowed to stagnate near the
places where we live. We must cooperate with the health
authorities when they visit to spray malathion and other
insecticides.
We must fix wired mesh to the windows and doors so as
to prevent mosquitoes from entering our house. We must use
mosquito curtains to protect us from them.
Activity 1:5 Observe where mosquitoes and flies are plentiful
around your house. Ascertain what conditions are necessary for their
growth and development. Are your surroundings and your house
clean? If not, try to keep them clean. Consult the health authorities
regarding the insecticides and the plan of action to destroy
mosquitoes. Educate your family members and your neighbours on
the importance of maintaining their surroundings clean and healthy.
Life Cycle and reproduction of the mosquito and the fly:
Figure 1.9 Life Cycle of Anopheles mosquito
12
The female mosquito is capable of laying about 100 to 1000
eggs at a time in stagnant water. The eggs of the anopheles
mosquito are boat like in shape. These eggs develop into worm
shaped larvae within a couple of days. They float on water and
feed on algae, bacteria and plants. After about 6 or 7 days, they
reach the pupa stage. They stay inactive and take rest without
taking any food during this period. In a day or two the adult
mosquito emerges out of this. This transformation from the
egg to an adult mosquito takes about 7 to 10 days.
Figure 1.10 Life Cycle of a Housefly
Flies develop in four stages. The female fly lays about 120
to 250 eggs at a time, on decaying organic matter, like animal
or human faeces, manure pits, rubbish heaps etc. The larvae
come out of the eggs within a short time of 3 to 24 hours. These
larvae do not have legs. They hide in rubbish or manure or
decaying organic matter. They cannot withstand light, but they
feed voraciously. They enter into the pupa stage by about 2 to
7 days and the adult fly emerges after 6 days. A pair of flies
(male and female) is capable of producing 325,200,000,000 flies
during a single summer!
13
Transmission through animals:
The animals we bring up as pets or the animals we rear
like the cow, buffalo, goat, sheep, cat, dog, pig etc. also spread
many microbes. These animals may themselves get infected
and become sick or may take part in the transmission of a
certain disease without getting sick themselves. For example, a
person drinking milk without boiling, or eating curds, ghee
and other milk products of a cow affected by tuberculosis, may
also get the disease.
The dreaded JE (Japanese Encephalitis) virus that causes
brain fever which results in physical and mental disabilities in
children, have domestic animals or birds as their host. When
their number increases enormously, they attack the human
beings. The affected child develops high fever, inflammation of
the brain because of meningitis or encephalitis, loses normal
consciousness.
Rabies or what is commonly known as mad dog bite
disease, is a viral disease. In the beginning the symptoms are
fever, headache, and fatigue etc. The victim suffers severe
muscular contractions. The victim's distress increases with
light and noise. Soon the victim starts shedding tears
profusely. He develops unreasonable anger, fear, especially
fear of water (Hydrophobia), difficulty in swallowing,
unconsciousness and finally end in death. These viruses are
usually found in dogs and cats. They multiply in them and
cause sickness to it. Even the saliva of these animals are found
to be contaminated with the viruses. When a human being is
bitten by a sick dog or cat, or even when a wound on his body
is licked by them, viruses enter the body.
Infectious diseases in animals caused by micro-organisms:
Micro-organisms cause a number of infectious diseases in
animals. If our pet animals and livestock are infected by these
diseases, we not only suffer losses but we may also be infected
and suffer heavily. For example: rabies, tuberculosis, brain
fever etc.
14
Anthrax: Goat, sheep, pig and cattle suffer from a disease
called anthrax which is caused by 'Bacillus anthrosis'. When an
animal gets infected and fall ill, fluids ooze from the eyes
which tym deep red. The animal will become inactive and
stands without touching its food or chewing the cud. Its
stomach bulges out due to constipation. It may also collapse
and die all of a sudden. At the time of such death, black
coloured blood oozes out from the natural opening like eyes,
mouth, anus, etc., of its body. Infection spreads to other
animals which come into contact with this contageous blood.
Since these bacteria can continue to remain alive in the skin
and hairs of the dead animals for years, the carcass of the
animal together with any other infected material made use of
by it must be burnt, or hurried in a deep pit away from water
1 sources. As a precaution, other animals must be immunised.
Foot and mouth disease:
Foot and mouth disease afflicts split-hoofed animals and is
caused by viruses. Blisters appear in the cleft of their hooves.
The sick ‘animals start shaking their legs continuously while
standing. Blisters appear in their mouth causing them a lot of
pain. They are unable to eat and secrete saliva profusely. The
blisters break down in three or four days to form ulcers. This
disease usually occurs during summer. The disease causing
viruses can be found in the milk of the sick animals. If children
drink contaminated milk without boiling they may also get
blisters and diarrhoea. It is beneficial ‘to immunise the cattle
before the commencement of every summer.
Diseases of the plant:
Fungi, viruses and bacteria are responsible for a variety of
diseases and destruction among many types of plants.
Fungal diseases: Yellow, red, brown, grey or white specks
appear on leaves, stem and other parts of the plant. The
diseased part dries up and looks as if they are burnt. The plant
sags and withers. Example: The disease which decays the root
15
Transmission through animals:
The animals we bring up as pets or the animals we rear
like the cow, buffalo, goat, sheep, cat, dog, pig etc. also spread
many microbes. These animals may themselves get infected
and become sick or may take part in the transmission of a
certain disease without getting sick themselves. For example, a
person drinking milk without boiling, or eating curds, ghee
and other milk products of a cow affected by tuberculosis, may
also get the disease.
The dreaded JE (Japanese Encephalitis) virus that causes
brain fever which results in physical and mental disabilities in
children, have domestic animals or birds as their host. When
their number increases enormously, they attack the human
beings. The affected child develops high fever, inflammation of
the brain because of meningitis or encephalitis, loses normal
consciousness.
Rabies or what is commonly known as mad dog bite
disease, is a viral disease. In the beginning the symptoms are
fever, headache, and fatigue etc. The victim suffers severe
muscular contractions. The victim's distress increases with
light and noise. Soon the victim starts shedding tears
profusely. He develops unreasonable anger, fear, especially
fear of water (Hydrophobia), difficulty in swallowing,
unconsciousness and finally end in death. These viruses are
usually found in dogs and cats. They multiply in them and
cause sickness to it. Even the saliva of these animals are found
to be contaminated with the viruses. When a human being is
bitten by a sick dog or cat, or even when a wound on his body
is licked by them, viruses enter the body.
Infectious diseases in animals caused by micro-organisms:
Micro-organisms cause a number of infectious diseases in
animals. If our pet animals and livestock are infected by these
diseases, we not only suffer losses but we may also be infected
and suffer heavily. For example: rabies, tuberculosis, brain
fever etc.
14
Anthrax: Goat, sheep, pig and cattle suffer from a disease
called anthrax which is caused by 'Bacillus anthrosis'. When an
animal gets infected and fall ill, fluids ooze from the eyes
which tyrn deep red. The animal will become inactive and
stands without touching its food or chewing the cud. Its
stomach bulges out due to constipation. It may also collapse
and die all of a sudden. At the time of such death, black
coloured blood oozes out from the natural opening like eyes,
mouth, anus, etc., of its body. Infection spreads to other
animals which come into contact with this contageous blood.
Since these bacteria can continue to remain alive in the skin
and hairs of the dead animals for years, the carcass of the
animal together w’ith any other infected material made use of
by it must be burnt, or burried in a deep pit away from water
sources. As a precaution, other animals must be immunised.
Foot and mouth disease:
Foot and mouth disease afflicts split-hoofed animals and is
caused by viruses. Blisters appear in the cleft of their hooves.
The sick ’animals start shaking their legs continuously while
standing. Blisters appear in their mouth causing them a lot of
pain. They are unable to eat and secrete saliva profusely. The
blisters break down in three or four days to form ulcers. This
disease usually occurs during summer. The disease causing
viruses can be found in the milk of the sick animals. If children
drink contaminated milk without boiling they may also get
blisters and diarrhoea. It is beneficial ’to immunise the cattle
before the commencement of every summer.
Diseases of the plant:
Fungi, viruses and bacteria are responsible for a variety of
diseases and destruction among many types of plants.
Fungal diseases: Yellow, red, brown, grey or white specks
appear on leaves, stem and other parts of the plant. The
diseased part dries up and looks as if they are burnt. The plant
sags and withers. Example: The disease which decays the root
15
portions of paddy and ragi crop is the blast disease. The field
affected by this disease appears as if it is burnt. The disease hits
the plants at all stages of growth and about 50 to 80% of the
crop is lost. Leaves of the paddy crop are covered by grey
spots due to a disease called 'sheath-blight disease' resulting in
the decay of the leaf sheath. In advanced stages, the grain
becomes hollow causing heavy losses to the farmer. Similarly,
grapes are affected by a disease due to fungus called 'powdery
mildew'.
Viral diseases: A number of plants wither losing their
vigour and brightness due to viral diseases. The green
coloured leaves and stem turn yellow. Some times parts of the
plant or the whole plant may rot. The diseases occurring in
chillies, ragi, maize, grape wines (yellow mosaic virus disease
and pear disease) are due to viruses. Sometimes the infected
plant may not show any signs of sickness. Such a plant spreads
infection to neighbouring plants without the knowledge of the
farmer. For example: Cucumber plant.
Bacterial diseases: The disease 'Late blight of potato' is
caused by the bacterium 'Pseudomonas'. The affected part
turns brown. When a piece of affected stem is dipped in water,
we can observe the bacterial mass emerging out like a white
thread. The bacterium 'Ervinis' causes the rotting of stems.
Agro bacterium Rhigogen is responsible for the formation of
hair like roots in affected apples.
Control of disease: There are several measures to control
the spread of diseases that affect plants.
1. Healthy seeds must be used for sowing.
2. The plot or land must be tilled well, cleaned and all the
unnecessary weeds must be removed.
3. The sick or diseased parts must be removed and burnt.
4. Fungicides and pesticides should be used as prescribed.
For example, sulphur, dithane, copper sulphate,
streptocyclin.
5. Insecticides that destroy insects which assist transmission
of microbes should be used.
16
Example: organophosphorus and similar compounds.
Activity 1:6 Visit a garden near your house or school. Observe
closely the shrubs, plants and trees that grow there. Search for
diseased leaves, fruits, flowers, stem or other parts of plants. Show
those collected diseased parts to an expert (An agricultural officer or
' a botanist). Learn from him about the affecting diseases, their causes
and methods of prevention. After a good understanding, write an
essay about the same.
Immunisation and Vaccines used in disease control
If weakened or attenuated microbes of certain diseases are
injected into animals or human beings, they bring about
immunity without causing that disease. The credit goes to
Louis Pasteur and Edward Jenner for the discovery of cholera
and small pox vaccines which are saving the lives of crores of
people.
There are two methods of Immunisation:
1. Active immunisation
2. Passive immunisation
Our body is capable of recognising immediately any
foreign body entering it. For example, protein substances that
enter our body encounter resistance from the body's defence
mechanism and produce antibodies. These antibodies in turn
destroy the foreign protein substances. These protein materials
which excite our body mechanism and generate antibodies are
named as antigens. Micro-organisms posses protein substances
that act as antigens. The antibodies develop due to these
antigens and fight against the invading microbes. In human
beings, spleen and the lymph glands are the organs where a
large amount of antibodies are produced. The antibodies
produced against the toxins of microbes are called
'Immunoglobulins'. The immunity of a human body depends
on the capability of the body to produce immunoglobulins,
and the presence of antibodies against antigens. This capability
is derived in humans from the following sources:
1. When in the womb, the infant gets immunoglobulins
17
through the placenta.
After birth, through the breast milk of themother.
When attacked by microbes.
When immunised.
It is very important that the infant is breast-fed right from
one day after delivery because mother's breast milk produced
during this period is rich in immunoglobulins as well as other
essential nutrients. People have a wrong notion that this milk is
not good for the child. This wrong notion must be changed.
In active immunisation, the antibody producing antigens
are introduced into the body system in order to produce
antibodies. This provides immunity for a certain period which
differs from disease to disease. Examples of this kind are B.C.G.
vaccination against tuberculosis, D.P.T. against diphtheria,
whooping cough and tetanus.
In passive immunisation, the antiserum containing
antibodies is administered to people.
Such vaccines give immunity against the disease for a
period of about six weeks. Examples of this kind are: Antiserum
used in the cases of diphtheria, tetanus, measles.
You might have observed vaccines are being given to
pregnant women and children by health personnel. They follow
the following table:
2.
3.
4.
Ideal Immunization Schedule
For pregnant women:
Early in Pregnancy
One month after T.T.l
Tetanus toxoid - T.T.l. (Injection)
T.T.2 or T.T. booster (injection)
For infant:
At 1 2 months
For tuberculosis
diphtheria
whooping cough
tetanus
for polio
At 21 months
18
B.C.G. (injection)
D.P.T. -1 (injection)
O.P.V -1 (dose)
DPT - 2 (injection)
O.P.V. - 2 (dose)
At 3 | months
At 9 months
for measles, mumps
and rubella
At 16-24 months
At 5-6 years
for diphtheria and
tetanus
for typhoid
At 10th year
At 16th year
DPT - 3 (injection)
O.P.V - 3 (dose)
M.M.R. injection
D.P.T. - 4 (booster
injection)
O.P.V. - 4 (dose)
diphtheria (injection),
T.T. (injection)
T.A.B. (injection, twice
with an interval of 4
weeks)
T.T. (injection)
T.T. (injection)
Even if late for an injection or immunization dose, one
must still get them, in consultation with health personnel.
Those preventive measures are very important for the life of an
infant, the young, as well as the old. By adopting these
beneficial measures, probable disabilities, that make a child
mentally retarded, due to brain damage etc. can be prevented.
The normal and regular physical and mental growth takes
place unhindered by decapacitating diseases and the child
develops, following a disease free growth pattern.
By the timely utilization of the benefits conferred by these
vaccines to all the children of the community, immunity of the
entire community will be taken care of and the catastrophic
striking power of these diseases is prevented.
Every individual must get himself suitably vaccinated
whenever an epidemic strikes. For ex: when a person gets
typhoid, the family must get vaccinated. When there is a case
of cholera, the entire village should be immunized against
cholera. Pilgrims and visitors to fairs and festivals should take
anticholera injections. If one gets wounded, antitetanus
injection is a must: Similarly, when bitten by a mad dog or a
street dog, antirabies injection is a must. One must not forget
the vaccination of the pet animals like dog, cat, cow and sheep
according to the advice of veterinary doctor from time to time.
19
Activity 1:7 Visit a general hospital and a veterinary hospital.
Ascertain from the staff regarding the vaccines to be given to human
beings as well as animals. To which diseases do they give protection?
Learn about the time gap of vaccinations, the number of times to be
given, etc.
Understand the sources of these antiserums and vaccines, their
preservation and how to maintain and protect their quality, their
effectiveness and the possible effects caused by them.
The cleanliness of the habitats where we live and bring up
our pet animals is also as important as getting immunized. We
should take care to see that our surroundings are kept clean,
free from dust, dirt, moisture, excreta, cowdung as well as
stagnant water. The flooring must be preferably of cement or
stone slabs, swept and washed every day. Disinfectants like
phenol could be sprinkled, often care also should be taken to
keep ourselves as well as animals clean. It is a healthy habit to
wash the body with clean water. Care must also be taken
regarding the grazing place of the animals. The advice of a
veterinary doctor may be taken before admitting a new animal
into the old lot.
Besides, if we and our pets eat nutritious food containing
proteins, vitamins, mineral salts etc immunity system of the
body will be further strengthened.
Preservation of food
Many of the foodstuffs get contaminated by microbes and
become stale. Such food stuffs are not fit for consumption. If
eaten it may result in vomiting, diarrhoea or sometimes even
death due to food poisoning. So, it is essential for the well
being of ourselves and pet animals, to store food in a scientific
way and protect it from microbes. There are different methods
to achieve this.
1. Heating and boiling:
By boiling the water and food that we consume, the
microbes present in them are destroyed. Do you now
20
understand, why soup or porridge which is kept unboiled get
spoiled and give bad smell?
Pasteurisation: The microbes that are naturally prevalent
in milk are Lacto bacillus, Lactis, strepto and staphylo cocci
mycobacterium tuberculosis and brucella. It is necessary to
heat the milk and kill the microbes. This is known as
pasteurisation. In some dairies, milk is heated by using steam
to about-l'40° to 160°C for a few seconds. By pasteurisation, the
microbes are destroyed and not the vitamin contents. The taste
of milk remains unchanged.
2. Removal of water content from food stuffs.
The reproduction rate of microbes increases in the
presence of moisture. If foodstuffs are absolutely dry and do
not have moisture, microbes cannot grow in them. Fruits are
dried from time immemorial, and preserved for use for a long
time. There are other examples . Raisin, dates, fish and meat in
dried condition can be preserved for a long time. While moist
cooked rice gets spoiled quite-soon, chapatis roasted on hot
charcoal or hot pan remain unspoiled for many days. Fungus
does not grow on the pieces of potato and mango fruit dried in
the sun.
3. Refrigeration
When the temperature in the surroundings is 5° C or less,
the growth and reproduction of the microbes is retarded. The
enzymes in them responsible for this activity become inactive
at low temperatures. That is why foodstuffs like vegetables,
fruits and other eatables kept in a fridge remains fresh for
several days. Have you now understood the advantages of
using refrigerators in dairies, vegetables, meat, fish stalls and
in medical stores?
4. Usage of sugar, salt and vinegar
From ancient times, salt has been used in preserving fish,
meat and pickles. Likewise sweets remain unspoiled when
21
they are kept in sugar syrup for a few days. Similarly 4% acetic
acid in vinegar preserves food items.
5. Chemical substances
There are certain chemical substances which do not harm
us but retard the growth of microbes. For example sodium
citrate, sodium benzoate, potassium-meta-bisulphate etc.
When sodium-benzoate is added to fruits juice and jams, they
remain fresh for a long time.
Activity 1:8 Visit a chemist's shop near your house. List out
the chemical substances used in preserving foodstuffs that are sold
there. Find out the details of their use. Visit a government food
godown. Collect information of the methods employed in the
preservation of food stuffs. Learn about the methods of preservation
from elders and your teachers. Discuss the principle behind these
methods.
Preservation of food grains
In olden days, villagers, used to preserve food grains in
underground vaults made of bamboos, mud and mortar. The
villagers took precautions to see that these Granaries were
moisture proof, thick walled, well protected and out of reach of
rodents. Even then, the so preserved grains were destroyed by
the attack of microbes. Nowadays, we have safe metal or
cement godowns wherein food grains can be stored. Chemicals
are used to prevent attack from microbes.
The following are the methods by which food grains can
be safely stocked and preserved:- Using cover lids to prevent
exposure to atmosphere, keeping away from insects, keeping
warm without moisture, usage of plastic bags which are non
absorbers of water, periodical spreading of the grains open in
the sunshine etc.
Preservation of cloth, leather and wooden materials
You must have observed that clothing material kept in
almirahs or in wooden boxes for a long time unused are found
22
tattered and eaten up by insects. You must have noticed your
mother removing costly silk clothes out of almirahs and
spreading them in sunshine. You may also be using moth balls
or napthalene balls to keep away cockroaches and other
insects. Clothes get spoiled more easily during rainy season
than in summer. Leather articles likewise get covered with
fungus during rainy season. Wooden materials painted with
varnish do not get wornout. But when not so painted with
varnish, they are eaten away by white ants. You must have
noticed that the bottom portion of the wooden piece which is
burried underground is coated with black paint or tar. Now
you know the reason for this practice.
Food poisoning
You must have heard that, sometimes an entire group of
people who have taken food at some function have developed
vomiting, loose motions, and stomach cramps. The reason is
that, the food they have eaten was contaminated with
poisonous substances. Such food poisoning can occur due to
many reasons but a majority of cases are caused by microbes.
If we consume stale food, particularly meat, then bacteria
called Clostridium perfringens will gain entry in to our
stomach.
Salmonella, a kind of microbes are found in foodstuffs
prepared in unhealthy surroundings. It is dangerous to
consume contaminated food. People may die due to food
poisoning. Therefore every precautionary measure should be
taken to ensure that food is safe for consumption.
Cooks and food servers must maintain bodily cleanliness.
Those suffering from skin diseases and wounds especially in
the hands, must not be allowed to serve. Otherwise they are
likely to spread a bacterium namely Staphylococci. Cooks and
servers should wear clean cloths.
The kitchen as well as the dining places must be hygienic
and free from dust, dirt, insects and other rubbish.
Cooking utensils and water used must be clean. One must
23
wash hands thoroughly with soap before eating. Finger nails
must be trimmed regularly.
Remember: Food poisoning can be prevented by taking
adequate precautions and maintaining cleanliness while
preparing, serving and eating the food.
Beneficial Micro-organisms
Even though many micro-organisms cause diseases and
are dangerous to us, some are very helpful due to their food
and medicinal value. They serve us as friends due to their
insecticidal properties. They even assist in our industries.
1. Food: You have already known about the role of
micro-organisms in dairy products like curds, butter, milk,
cheese, in making bread, jam, dosa, idly, pickles etc. Algae
serve as food for fish and thus indirectly provide food for
us through them.
2. Medicine: You have observed that doctors prescribe
penicillin injection, tetracycline capsules, erythromycin
tablets, gentamycin drops or ointment for treatment of
infections (sore throat, cough, pus formation in the ear,
inflammation of the eyes, brain fever or meningitis,
urinary infection and during surgery etc). These
antibiotics are all derived from micro-organisms.
A particular substance produced by one kind of
micro-organism may retard the growth and replication of
another micro-organism or may even kill them. The substance
may break open the outer shell of the micro-organism or
destroy the inner membrane or prevent the formation of
proteins which are necessary for the growth and
multiplication. Such a substance is called ANTI BIOTIC. Sir
Alexander Fleming discovered the first antibiotic. 'Penicillin'
from a fungus called Penicillium notatum' in 1928.
Activity 1.9 Make a list of the antibiotics commonly used (with
the help of a doctor). Try to understand the precautions to be taken as
well as the side effects of such antibiotics.
24
NITROGEN FIXATION
Figure 1.12 Roots with nodules
25
You already know that the air in our atmosphere contains
nitrogen, oxygen, carbon-di-oxide and other gases. Nitrogen,
which is an inert gas can also exist in different forms in rocks,
soil, plants and animal bodies. Study carefully the details in
figure 1.11 showing nitrogen cycle.
1. Nitrogen which is in the form of a gas mixed in air, is
sucked by a type of bacteria called rhizobium which are
found mainly in the roots of leguminous plants like horse
gram, pea, soyabean etc. These bacteria convert nitrogen
into nitrates. These nitrates are taken in by plants and
converted into proteins.
2. During thunderstorms, the inert gas nitrogen in air
combines with oxygen and mixes with moisture to form
nitric acid. Nitric acid gets down during rains and
absorbed in the soil. The salts contained in the soil react
with nitric acid to form nitrates. Plants utilize the nitrates
so formed.
3. Not only rhizobium, other bacteria and blue green algae
also participate actively in the process of nitrogen fixation.
4. Dead and decaying plant and animal matter (Biomass) get
converted by the denitrifying bacteria contained in the
soil. During this process, nitrogen gas gets released back
into the atmosphere.
5. Bacteria present in the soil react and start the process of
decay and disintegration of any form of biomass. (Plant or
animal matter) During this process the excess protein
material of the biomass is converted to ammonia.
Ammonia dissolves in the moisture content of the soil. By
the action of bacteria which live and grow in soil,
ammonia is converted as nitrates. Nitrogen as fertilizers
enrich the growth of plants. All plants utilize it.
Conservation and maintenance of the soil
We bury dead animals in the soil. In about a few days, the
burried bodies get disintegrated and mix with the soil, except
for the bones. Likewise all dead animals, leaves, flowers, stem
etc falling on the ground also become a part of the soil. Such a
26
soil is fertile and is known as 'Humus' (fertilized soils). Humus
is very essential for all plant life, especially for food and
commercial crops. The role played by micro-organisms in the
formation of humus has no parallel.
Microbes actively participate in the maintenance of the
ecological balance of our surroundings. Imagine what would
have happened to our surroundings in the absence of
microbes! The whole earth would have been full of dead and
decaying matter of animals and plants. Our lands would have
been turned into deserts, due to the absence of humus and
plants. Hence, if at all, we imagine a world without microbes,
we have to imagine a world without any life.
Uses in Industries: Yeast is very useful in the preparation
of alcohol, which is widely used in many industries. Different
types of microbes are used in the manufacture of organic acids
and antibiotics. Fungi are capable of increasing the yields of
enzymes. These enzymes assist in the metabolism of
carbohydrates, proteins, and fats. Enzymes are useful in
tanning industry because they assist in the removal of hair
from the skin easily. Algae assist in the manufacture of iodine,
agar, certain mineral phosphates and nitrates. Some bacteria
are used in the purification of certain mineral ores.
Biological control of pests
The microbes which causes diseases in insects usually do
not harm animals or plants. Some of these are used in
controlling pests which destroy food and commercial crops.
This is called biological control of pests.
EXERCISE
I.
Answer the following questions:
1.
2.
Point out any two special features of micro-organisms.
"Micro-organisms can be man's enemies as well as friends"
Explain.
List any four diseases caused by microbes. Explain the different
3.
27
4.
5.
6.
7.
8.
. 9.
10.
11.
12.
methods by which those diseases are spread.
How do microbes come into contact with water? •
What are the roles of man and mosquito in the life of a malarial
parasite?
What is 'Pasteurisation'?
What are vaccines? When are they to be given to the child and
pregnant women?
Name a few diseases caused by microbes in pet animals.’ How
can they are prevented?
What are antibiotics? Give two examples.
Which methods are used in the preservation of foods?
What is meant by 'food poisoning'? How can this be
prevented?
What is the role of microbes in the conservation of fertility of
the soil?
II.
Choose the correct answer and mark (a/) against the
correct answer.
1.
The pioneer who drew attention towards the existence of
microorganisms as well as responsible for the discovery of
vaccination is
a.
Robert Koch
b.
Louis Pasteur
c.
Joseph Lister
d.
Alexander Fleming
The smallest among the following
a.
bacteria
B. algae
c.
virus
c. protozoa
Cholera is caused due to,
a. drinking impure water
b. curse of village diety or God
c. deficiency of nutritious food
2.
3.
4.
d. deficiency of oxygen in the atmosphere
Rabies occurs
a. When an infected dog bites
b. when a dog licks our skin
28
5.
6.
c. by a fly or through air
d. only in children
The chemical substance used in the preservation of food is
a. Potassium permanganate.
b. Ethyl alcohol
c. Potassium meta-bi-sulphite
d. Copper sulphate.
A child may suffer from polio due to
a. the Sins committed by parents.
b. the incomplete dosage of polio drops
c. Witchcraft
d. Diphtheria
m. Match the following:
B
A
i.
a.
b.
c.
d.
7.
a.
b.
c.
d.
Disease
Micro-Organism
a..
b.
Amoebic dysentry c.
d.
Tuberculosis
e.
Disease
a
Rabies
b.
Typhoid
c.
Cholera
d.
Tuberculosis
e.
Protozoa
Bacteria
Virus
Algae
Bacillus anthrosis
Carrier of germs
Air
Pig
Fly
Water
dog
Preservation method
Use of Sodium benzoate
Pasteurisation
Flu
Anthrax
Food
3.
a.
b.
c.
d.
Pickles and Meat a.
b.
Jam and Juices
Grapes and
mangoes
c.
d.
Milk
29
Salt
Drying
Chapter 2
ADAPTATION and ORGANIC EVOLUTION
Organisms live in different types of environment. Many
animals and plants live on land, some others live in water.
Organisms have adapted to their environment by adjusting
their living activities. Organisms adapt themselves to the
changes taking place in the environment. Because of this, all
the organisms can survive and continue to reproduce.
Activity 2:1 List the names of animals and plants that live on
land. List the names of some animals and plants that live in water.
List the organisms that live in sail.
The environment of organisms has a number of things or
factors which form the environment namely soil, water, air,
light, temperature etc.
There are many types of environment on our earth. For
example, cold regions covered with snow, torrid regions where
temperature is high, desert with sands, oceans with salt water,
forest covered with dense plant life. Living things in these
different environments live by adapting their life pattern to the
surroundings and to their environmental condition. Because of
these reasons there are variations in the structure of living
things. Camels living in deserts and cactus are different from
fish and lotus which exist in water. We can see variations in the
body structure and life functions of living beings according to
the environment in which they live.
Activity 2:2 Mark the deserts, torrid regions, dense forests in
the map of India and find out the names of some animals and plants
which live in these regions. List the names offive animals living in a
well and five animals living in sea.
Organisms have the ability to adapt because of certain
structural features in their organs and living characteristics in
tune with their environment. For example, fish in water,
camels in desert, monkeys which live in trees, pigeons that fly
in air. There are differences in the body structure and functions
30
of these animals. All these animals have adapted to their
environment. Fish cannot live in sand and camel cannot live in
water. The reason for this is that a particular structure of their
organs helps them to adapt to a particular type of environment
adapted by them.
Activity 2:3 Observe the body structure of the fish and the
pigeon. List the features of their organs which help them to adapt to
their environment.
Body structure of fish
The body of a fish is boat shaped. This shape helps fish to
move about efficiently in water. The fish has fins for
swimming. It has gills which draw out oxygen dissolved in
water. In this way, gills, fins and the body shape function in a
unique manner to make tire fish live in water.
Activity 2:4 Draw a diagram of a fish and label the parts.
Observe the gills, fins and the shape of the body offish.
Body structure and adaption of Camel
Camels live in deserts. In deserts, water is scare and
temperature is high. Camels very often live without drinking
water for 15 days. The camel's skin is protected from heat as
there is a fat layer under the skin. Owing to this, camel can live
comfortably even in temperatures of 34cC to 40°C. Because the
kidneys retain much water and release little quantity of water
by way of thick urine, the total water content of the camel is
retained at a comfortable level. The camel has a four
chambered stomach which facilitates the digestion of rough
type of vegetation that it eats. The camel has strong teeth. The
skin layers in its mouth are thick. In this way, camels have
adapted themselves to their environment and have survived.
Body structure of pigeon and its adaptation
Pigeon, a common bird is well adopted to aerial mode of
life. A bird's body structure is different from that of other
animals. To suit its life in air, its bones are light to facilitate
31
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flight. The fore-limbs have been modified into wings. There are
feathers on its body. The shape of its body is pointed. So it can
pierce through the air and fly.
Activity 2:5 Draw a sketch of a pigeon and label its external
parts. Study its beak, feet and food habits.
Like animals, plants also have to adapt to their
environment, failing which they cannot survive and become
extinct.
There are unique structural features in aquatic plants plants that live in water. For example, roots are short, there are
air chambers in the stem and the stem is soft.
Activity 2:6 Observe lotus, valisnaria plants and list the
structure and characteristic of their parts.
If we study the structure of a cactus plant, it is easy to
leam about the adaptation in plants. Cactus normally grows in
dry and sandy areas. In this plant, the stem keeps it always
moist. The leaves are like thorns. All these modifications
facilitate the cactus plant to adapt to its dry and inhospitable
environment. Since the stem is green, it participates in
manufacturing food. As the leaves are modified into thorns,
transpiration (evaporation of water) is prevented and keeps
the cactus plant moist always.
Activity 2:7 There are many species of cactus. Observe a
common cactus like Opuntia. List the differences between bean plant
and Opuntia
Water, air, light and temperature have their effect on
organisms in different ways. These factors have tremendous
influence on the adaptations in organisms. As a result of this
changes in the body structure and functions of the organisms is
a continuous and ongoing process.
Example: The evolution of aquatic animals into "terrestrial
animals has taken place because of many changes in the
structures and functions. Formation of legs facilitate
movement, blood stores essential water content and also has
protective mechanism, fertilization occurs within the body etc.
32
Animals and plants that live in cold regions also exhibit
adaptations. They do not get water in the winter season as
water becomes ice. At that time trees shed their leaves. This
helps the plants to prevent transpiration, and retain water
within the body. Hence shedding of leaves indicates
adaptation.
Activity 2:8 The polar bear lives in the polar region and the
camel lives in deserts. Make a list of the body structures which help
in their adaptation.
Organic evolution
When you look around you, you will see hundreds of
types of animals and plants. You will wonder whether all the
living things were created at the same time, or in stages. Such
questions have been pursued by many people from a long
time. However, it is difficult to answer these questions
accurately. But scientists have come to certain conclusions on
the basis of their observations and study.
Hundreds of millions of years ago, when the earth was
born, it was not like what it is now. The earth was a ball of hot
gases. Gradually, the earth began to cool and its outer cover
solidified and was converted into rocks and stones. Slowly,
mountain ranges and oceans were formed. Due to incessant
rains, oceans and seas were formed. Extremely simple
organisms were created first and they increased in number and
variety, finally resulting in the formation of animals and
plants. This continuous process of gradual change from simple
forms of life into complex organisms is called Organic
evolution.
The earth is a planet. Life appeared on the earth millions
of years ago. Life was created when many simple things on
earth underwent chemical changes continuously and modified
into very complex support mass also called biotic soup from
which life emerged.
Organisms that lived oh earth 150 crores years ago were
protozoa, bacteria, unicellular organisms algae and molluscs.
33
These organisms lived for a long time and went on adapting to
their environment. About 18 crore years ago some reptiles
appeared on earth. Some examples are giant reptiles like
dinosaur, tyranosaurs. In course of time they became extinct.
Later, birds and mammals appeared. The earliest man must
have appeared about 20 lakhs years ago. Animals and plants
have been continuously showing changes in a slow pace in
order to adapt to the changing environment. Even now
organisms are changing.
How did organic evolution take place? Why did it take
place? Charles Darwin was the first biologist who gave
satisfactory explanation to these questions.
Exploration of the earth and fossils
These studies will indicate that the earliest organisms had
very simple structure. It is most likely that these simple
organisms evolved gradually into complex organisms. These
are definite evidences to show that this slow change has
indeed occurred and continues to occur.
Important evidences are fossils, structural and functional
features of organs and embryology.
Fossils
From ancient times, the entire body or organs of some
organisms or imprints have been preserved in the layers of the
earth. These are called fossils. Fossils may be the skeletons,
shells, the marks of the feet of animals or may even be plants.
The fossils of animals or plants that lived thousands of years
ago may be found in the layers of the earth.
Fossils as evidence
From the study of fossils, we can make out the structure of
the body of animals and plants that lived long ago. By
comparing them with the body structure of the present
organisms, the resemblences and differences become clear. On
the basis of this, we can deduce how a particular form of
34
organism might have been modified gradually to evolve into
the present day organism.
The oldest fossils discovered in rocks belong to the simple
forms of life and the recent ones relate to the complex forms.
From this, one can deduce that complex forms of life are really
modified from the simple forms existed before.
Observe the picture of an Archaeopteryx which lived long
ago and has become fossilised. It had teeth as in reptiles, wings
and beak as in birds. The fore-limbs had become wings. To
establish this, we find fingers with nails in the margin of the
wings. It had a long tail of a single feather.
From the careful examination of such fossils it becomes
clear that some animals belonging to the reptile group have
gradually changed to birds of today.
There are fossils of plant forms also. All these fossil
evidences support the theory of evolution.
Figure 2.1 Archaeopteryx
Structural and functional evidences. It we study the
anatomical pattern of the forelimbs of some animals and the
human hands, we see some similarities and some differences in
them. Observe the flippers of the seal, the whale, wings of bat
(mammals) fore-limbs of a horse and human hand. The
35
structural pattern of the bones are similar. But, due to
differences in activities to suit a particular -environment,
differing structural adaptations have emerged.
Figure 2.2 Fore-limbs of some vertebrate animals
If the basic structure is the same but functions are changed
forced by adaptation, then, such findings support the theory of
evolution.
Sometimes, the basic structural make up may have been
different, but on going process of evolution forces the
adaptation to obey the requirements of ecological
surroundings.
Example: The wings of birds and butterflies are different
in their structure but their function is the same. This shows that
according to functional requirements there may be evolution in
organic structures.
36
Figure 2.3 Wings of insect, bird.
Activity 2:9 Make a list of similarities and differences in the
structure of wings of butterfly and a bird.
Embryological evidences:There are some similarities in the development of plants
and animals. All organisms start their development from a
single cell. If the development of the embryos of some animals
is studied, it can be seen that, all organisms develop from a
single cell. The embroyos of all vertebrates (animals having
back-bones) have some similarities in the beginning stages.
Later on, they develop variation in their individual
characteristics.
Activity 2:10 Study the embryos of these animals. Fish,
amphibian, bird and man.
When the figures 2.4 are studied with care and compared,
we learn that amphibians birds and mammals start from the
stage of fish-like from, and have undergone changes or
evolved into their present form ■ due to environmental
pressures.
37
Fish
Chick
Frog
Figure 2.4 Stages of development of embryos
38
Man
Activity 2.11 Observe the following figure and write the
changes found in the neck of Giraffe
Figure 2.5 Evolution of giraffe according to Lamarck
Theories of organic evolution:
There are two important theories of organic evolution.
They are
a. Lamarck's theory of use and disuse of parts, (known today
as the theory of inheritance of acquired characters)
b. Darwin's theory of natural selection.
a. Lamarck's theory of use and disuse of parts
Study the figure 2.5 carefully. By comparing the picturised
versions of evolution, we can guess how the giraffe's neck got
elongated. un the basis of Lamarck's theory. By using their
necko and front legs continuously to eat the leaves in the tali
trees, the necks and front legs of the giraffes grew long.
39
Therefore the modem giraffes have long necks and legs.
The same reasoning also argues that since snakes were
crawling their hands and legs became useless and gradually
they lost them. Therefore, the present snakes are limbless.
The appendix in human body remains without use.
Similarly unused is the third lid membrane of the eye.
b. Darwin's theory of evolution based on natural selection.
Charles Darwin published his book titled "Origin of
Species by Natural selection" in 1859. In that book, he has
explained with many examples how organic evolution has
taken place according to him. It is natural for all organisms to
reproduce in excess. Such excessive reproduction create a
struggle for existence, i.e., a severe competition for obtaining
life supporting requirements like food, water, living space etc.
Figure 2.6 Charles Darwin
40
This results in the destruction of many organisms before
they attain the age of reproduction. Only those few capable
organisms which fight and survive, will be able to reproduce
and live successfully. Darwin called this process as the
"survival of the fittest". This means that the nature itself selects
some organisms as fit to live and reproduce. He termed this
process as "natural selection". Accordingly, it is claimed that
man is at the pinnacle of evolution.
In this way, nature, by the process of natural selection, is
causing variation in organisms and is producing new and
different species.
EXERCISE
1.
2.
3.
4.
5.
6.
List four inorganic substances.
What is environment? How many types of environments are
there? Make a list.
Fill up the following table with appropriate organisms.
Aquatic animals
Animals and plants
and plants.
living in deserts.
Animals
Animals
1.
1.
2.
2.
3.
3.
Plants
Plants
1.
1.
2.
2.
3.
3.
What are the important adaptations in the body structure of
the fish which help them to live in water?
Which important features of pigeon's body structure help it to
fly in air?
What are the modifications in the cactus which enable it to
adapt to dry climate and desert regions?
41
7.
8.
9.
10.
11.
12.
13.
14.
The plants that grow in Tundra region shed leaves during
summer. What is the advantage of this to these plants?
What are the important characteristics of the body structure of
camels which help them to adapt to the climate in deserts?
What are fossils?
List the names of animals that are imprinted on two fossils.
What do we learn by studying structural and functional
characteristics of organs?
What is Lamarck's theory of evolution called? Explain.
What are the important points of Darwin's theory of
evolution?
What is meant by organic evolution?
42
Chapter 3
USEFUL PLANTS AND ANIMALS
Plants, animals and micro-organisms influence our life in
many ways. While some organisms are useful to us, some
others are harmful. In summary, in order to live we depend
upon many organisms. The food material, medicines, clothes,
furniture and other materials that we need, are products
created by the assistance and activities of many Organisms. It is
also true that many of the useful things we need are destroyed
by micro-organisms and insects.
Activity 3:1 List some plants and animals used for food. List
some names of things of plant and animal origin that we use
everyday.
Plants are useful to us in many ways. Plants give us food
materials. Plants store food they have produced with the help
of sunlight in different forms. Such stored plant food materials
are consumed by all forms of animals as their food.
Activity 3:2 List the names of food materials obtained from
plants.
Observe pulses and different vegetables and list out their names.
Due to green revolution in our country, vegetables, pulses,
tubers, grains and other food yielding are being grown by
adopting modern methods.
Activity 3:3 In the map of India, mark the names of places
where different food crops are grown.
For wood required for construction of building and
furniture, we utilise different species of trees like teak,
casuarina, honne, rose wood etc. Therefore, we put to our use
and comfort many materials drawn from plants.
Activity 3:4 List useful things made from trees (Wood).
We use roots, leaves and nuts of some plants as medicine.
Ginger, pepper, clove, baje are used by the Ayurvedic system
of medicine to cure many diseases. The ayurvedic system of
43
medicine has been in vogue in our country from ancient times.
In this system, medicines prepared from plants are used to
cure many diseases.
Activity 3:5 Visit an Ayurvedic Hospital and know the names
of medicinal plants.
Beverages are prepared from the parts of some plants. For
example, millions of people drink beverages prepared from
coffee, tea and cocoa. Similarly plants like rubber, jute, cotton
are used for jnanufacturing clothes. Scents and colognes are
manufactured from plants like rose, jasmine, champak, sandal,
pandams etc.
Activity 3:6 1. List the names of temple handicrafts in Karnataka.
2. List the source of plants used in these handicrafts.
3. List the places where rubber is grown. If possible visit a rubber
plantation and learn about the production of rubber.
Because of plants, our atmosphere is cool and the air is
fresh. Since plants are very useful, we should grow plants and
also protect them. Plants should never be destroyed.
Activity 3:7 How many beautiful gardens exist near your
house? What species of plants grow there? Find out and write notes
on the programme of the Karnataka Government to protect plants.
Our economic condition improves by selling plant
products. Substantial profits can be earned from plants like
coffee, tea, tobacco, coconut, paddy, sugarcane.
Activity 3:8 List the crops grown in the fields near your house.
Write notes on the crops which have economic value.
Animals have been useful to us since ancient times.
Animals help us in transporting things. They provide us food,
wool, silk, lac, shell lime, pearls and other things of utility.
Animals used as food
Fish, crabs, prawn are used as food by many people. Since
fisheries are being run in an organised way, it has become
possible to get good species of fishes for food.
44
Activity 3:9 Observe a nearby fishery. List the names of edible
fish grown and supplied.
Eggs, like milk, are also rich in nutrients. Chickens are
used as meat.
Activity 3:10 Visit a nearby poultry farm. Learn what
arrangements are made to rear chicken.
The flesh of goats, sheep,, pigs and other animals are used
as food. In some countries, flesh parts of animals like giraffe,
buffalo, cow, mule, frog, snake etc., are taken as food. Dairy
products are got by many types of modern projects.
We obtain milk from cows, buffaloes and goats. Recently,
great developmental activities have taken place in dairy
farming. Huge quantities of milk, butter and ghee are being
produced. Modern dairy processing has improved the quantity
and efficiency of diary products.
Activity 3:11 Find out about the activities of government dairy
farms. If possible, visit one.
Bees gather honey and pollen from flowers and provide
honey and wax. Honey is used as food and medicine.
Activity 3:12 Visit apiaries and collect facts about the methods
of rearing bees and producing honey.
Silk worm feeds on mulberry leaves and grows. The
caterpillar that comes out of the egg eats vigorously and grows
into pupa stage. It then secretes the silk yarn from its salivary
glands and builds its cocoon. These cocoons are boiled, the
worms with-in are killed and silk yarn is spun out. Expensive
silk cloth is woven from the silk yarn. Silk cloth produced in
Karnataka is exported to other countries.
Activity 3:13 Visit a nearby place where silkworms are reared.
Study the way the silkworms are reared. Also study how silk cloth is
produced.
After killing certain animals and using their flesh as food,
their skin is removed and tanned. Skin can be used to make
many things. For example, the skin of animals like cow, buffalo
45
and horse is tanned and is used to make footwear, belts, bags,
musical instruments and other useful tilings. The Karnataka
government has launched many projects to encourage leather
craft.
Activity 3:14 List the names of things made from skin. Visit a
nearby leather factory and collect information about the process of
tanning skin.
The shells of animals that live in rivers and oceans are
used for many purposes. They are used in preparing lime
which is used in the construction of buildings. Shelled animals
like oysters are reared and precious pearls are obtained.
Activity 3:15 Collect animal shells to understand their variety.
observe their colour, pattern and structure.
Wild animals like tiger, lion, elephant, rabbit, deer,
crocodile are killed indiscriminately. Many types of colourful
things are made from them. The government has prepared
plans to prevent unwanted killing of wild animals.
Activity 3:16 Make a list of ornamental things made from
animal sources which are sold in the market. Discuss whether they
are really useful to us. Correspond with the forest department and
collect information about preservation of wild life.
Rearing animals has been a hobby from time immemorial.
While some animals like the dog, cat, parrot, snake, bear, tiger
are kept for pleasure, other animals like rabbits, rats and
guinea pigs are used in laboratories for experiments. In recent
times, animals are used in for space exploration and
investigations to find out the effect of newly discovered
medicines.
Activity 3:17 Make a list of animals used in laboratories for
experiments.
Which animals are used for space investigation?
Harmful plants and animals:
While many plants are useful to man, a few other plants
are harmful. Some times, plants cause damage by being
46
harmful to other organisms also. Some parts of plants may
cause disease in man. For example, parthenium is causing
health hazards in recent times. If parts of these plants are
touched, our body suffers from skin diseases, cough, asthma
etc. Certain type of mushrooms are poisonous.
Activity 3:18 If there are harmful plants near your school find
out their names and the harm caused by them.
Decayed and spoifed parts of plants may also be
poisonous.
Some animals are also harmful. Insects destroy many
useful things in our environment. Insects like cockroach,
termites, locusts, ants, cause loss of materials worth crores of
rupees every minute.
To destroy these insects, scientists are experimenting and
discovering many insecticides. Insects are destroying
thousands of tons food every year. Furniture and other
substances are also destroyed by insects. Such harmful action
can be prevented by taking suitable remedial measures.
Activity 3:19 List the names of things destroyed by termites.
Explain how furniture is affected by termits. Explain what methods
are followed in your houses to destroy cockroaches.
Some animals spread dangerous diseases from person to
person. Mosquitoes spread malaria and filaria. Flies spread
cholera and dysentery. Rats spread plague. Therefore, we must
keep our houses and surroundings clean and free from such
insects and pests.
Activity 3:20 Observe what actions are undertaken to control
mosquitoes. Explain.
Know how insects like bugs are destroyed.
EXERCISE
1.
2.
3.
List the names of 15 plants used for food.
What is meant by the green revolution?
List the names of furniture made from teak wood.
47
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
List the names of useful things made from leather.
What is afforestation? (Vana Mahotsava)
If forests are destroyed, nature's balance is upset. How?
What is a sanctuary? What are its uses?
Why are eggs considered as wholesome food?
What are the advantages of a dairy farm?
Name 5 plants used for medicinal purposes.
Mention the uses of animal shells.
Name the programmes launched by the government to protect
wild life?
What are the health hazards caused by parthenium plants?
What methods are followed to control parthenium?
Mention the harm caused by cockroaches, termites and locusts.
How are they controlled?
48
Chapter 4
CONSERVATION OF NATURAL
RESOURCES
Crores of people and countless Organisms live on the
earth. All these organisms depend on a few vital natural
resources in order to live. Solar energy, oxygen, water,
carbondioxide, minerals are a few essential things required.
Since these things are available in nature in abundance, they
are called natural resources. Solar energy is the most
abundantly available source of energy. Similarly, water and air
are also natural resources.
Activity 4:1 List the natural resources available in nature.
Which resources are stored by man. Make a list of gadgets used to
obtain solar energy for our benefit.
We obtain most of our essential natural requirements,
from the surface of the earth by mining and digging the earth
and also from the atmosphere. We get solar energy, the source
of all forms of energy in the form of light and heat from the
sun. Natural resources are available in different forms.
Oxygen, carbon-di-oxide, nitrogen are abundant in the form of
gases. These gases are needed by all organisms for their life
processes.
Water and petroleum are the most important forms of
liquid resources. Water is found in rivers, oceans and under
the ground. We all know the importance of water. Petroleum is
stored in the earth. Human Activities would be adversely
affected if these petroleum products were not there. Minerals
which are solid form of natural resources, occur inside and also
on the surface of the earth. We all know the uses of minerals.
Soil is essential for the growth of plants. Soil also is one of
the natural resources. Without soil, it would be difficult to
construct buildings. Natural resources in different life forms
are available as forests, animals and their products as
49
medicines and food materials.
Activity 4:2 List the natural resources found on the surface of
the earth
List the importance of natural resources. Mark the places where
minerals are found in the map of India.
Activity 4:3 Mention the uses of water. Mark in the map of
India, sancturies where wild animals are protected.
List the uses of the plants that grow in forests.
Natural resources can be grouped in two ways. Some
natural resources can be reused even after repeated uses. Such
resources are known as renewable resources.
For example: It is possible to renew water, air,nitrogenous
matter and food materials.
Yet, if there is indiscriminate and excessive use of earth,
seas and forests by man for his demands of life, like buildings
and energy, the balance in nature may get disturbed.
Therefore, these natural resources have to be used and
renewed in a systematic and innovative manner.
Forests are being destroyed for timber, fuel and sites are
cleared for buildings. If forests are destroyed, many natural
resources are also destroyed. For example, there will be defects
in watercycle and untimely rainfall, destruction of crops,
danger to wild life, erosion of soil etc.
Activity 4:4 Know the plans for reneiual of forests. How will
nature be affected by construction of dams? What are the ill effects, if
unwanted things are dumped into the seas?
Water resources are essential for living process and we are
using them in a variety of ways. We use water for drinking, in
industries, for irrigation and to produce electricity etc.
Water resources can be renewed. But for this process,
assistance of plant life is essential. Plants absorb underground
water and release it to the atmosphere through transpiration.
Clouds are formed and generate rainfall supplying water to
the sources. By deforestation, the rate of transpiration from
plants is reduced and the water cycle gets affected. This causes
50
many changes in the atmosphere.
Activity 4:5 There are many plans to utilise the water
resources. Collect information about this and organise a science
exhibition. Study the water and air cycles.
Activity 4:6 Know about recent activity in the field of food
processing. Know more about the effects of deforestation, rendering
more land for irrigation etc.
Know the programs for using and increasing the products offish and
other sea products.
We use many things available in the earth for our needs
and progress. But such utilisation is increasing day by day,
with the result they are getting more and more scarce.
Minerals, petroleum oils, coal and such things are getting
scarcer. It is not possible to renew or produce these materials
by us. These materials are called non-renewable resources.
Since these resources are available in limited quantities and
take a very long time for their formation they have to be
preserved and we have to plan for their controlled use.
Activity 4:7 Find out reasons why coal utilisation is reduced.
Find out at what depth in the earth petroleum oil (crude) is found.
We use energy in different forms. Electricity is a form of
energy. Likewise, petroleum is also a form of energy. Indeed
all energies are different forms of solar energy. Since we have
abundant sunlight, we must try using more solar energy.
Nowadays, many industries have started using solar energy.
Solar energy is used to boil water and run machines from the
steam thus got. Solar energy is also used for cooking in many
houses. Solar ovens can be easily manufactured.
Activity 4:8 If there are solar energy ovens manufacturing
factories nearby, visit them.
You can also prepare solar energy ovens with the help of mirrors.
Air, water, forests and mineral wealth which are in limited
supply are put to increasing uses day by day. The reason for
this is the growing human population. We are using all natural
resources excessively and unsystematically.
By cutting down trees in the forests we are destroying the
forests. Deforestation causes natural imbalance. It has many
evil effects such as erratic climatic changes, Soil erosion,
changes in the water cycle, loss of many animals and plants. It
is for this reason, reforestation programmes are undertaken.
This increases plant wealth and maintains the natural water
cycle and climatic balance.
Activity 4:9 Know why the Silent Volley project in Kerola
State has been stopped.
How many plants and trees are generally destroyed for laying out of
a residential colony?
List the inconveniences caused to animals by this.
How much forest and how many animals are destroyed when a dam
is built? Discuss.
We are changing the natural features in recent times by
excessive and unsystematic use of the natural resources.
Deforestation, construction of dams, starting industries, atomic
energy centres, fertilizer factories, founding of big cities and
other man made environmental changes are putting undue
pressure on the natural environment and increasing pollution.
Due to these activities, there is pollution of air, water food
and the very land we live on. These are causing harm to our
life. Many hazards are also caused recently due to radiation.
All these activities are deforming the structure and
character of our environment and are destroying natural
resources.
Activity 4:10 List the types offertilizers used in agriculture.
List the ill effects of the Chernobyl accident in Russia.
List the activities that pollute the environment.
List the various plans to preserve forests.
To preserve and use the natural resources systematically,
governments have prepared major plans. Governments have
also implemented many community projects to preserve
forests and protect wild animals. They have also introduced
planning and control of big cities and industrial growth.
Unlike before, dams are built with an eye on ecological
52
repercussion.
At the national level, important projects are: soil
protection
and
conservation
projects,
afforestation,
reforestation, and sanctuaries, environmental and water
control programmes. All these efforts are intended to protect
and systematize the innovative use of our natural resources.
The outer layer of the earth where plants grow is the
fertile soil. This soil contains important minerals, nitrogenous
matter and salts which are essential for the growth of plants. In
addition, this soil contains a variety of bacteria. In order to
prevent soil erosion many 'soil conservation projects' have
been initiated.
Activity 4:11 Visit a nearby soil preservation centre and
collect information about the projects there. Organise an exhibition of
the various projects.
The forests departments have prepared reforestation
projects. Important activities under this are growing new
forests, planned method of growing plants, preventing
destruction of forests. There are National Forest Research
Centres where research is carried on in forest development
activities. Forests are grown on shallow lands, deserts and hilly
regions.
Activity 4:12 Visit a nearby forest department. Study its
programmes. Observe the activities of the forest department during
your journey.
Activity 4:13 Visit Nagarhole, Bandipur and such places.
Know activities that are undertaken there,
Correspond with the forest department and collect more information
about preservation of wild life.
To protect wild life, the government has many projects
and has been systematically maintaining many sanctuaries
Nagarhole, Ranganathittu and Bandipur are such sanctuaries.
Try to know how wild life is preserved there.
Air, water and atmosphere belong to all living beings.
Therefore at the international level many rules have been
53
framed as an attempt to protect natural resources. If these
resources get diminished, our life may be destroyed. Therefore,
all of us should join in the efforts in preventing the excessive
use and pollution of our natural resources.
EXERCISE
1.
List 10 natural resources that are available inside the earth.
2.
Mention activities that are performed using solar energy.
3.
4.
Which gas is required for life activities of organisms?
What are the disadvantages of continuously using petroleum
oil found underground?
Which natural resources are renewable?
What is meant by natural water cycle? What is the relationship
between deforestation and water cycle?
5.
6.
11.
How can water resources be renewed?
What programmes are there to renew the sources of food?
What is meant by green revolution?
Substantiate the statement that all energies are different forms
of solar energy.
How do you support the argument that it is not possible for us
to lead healthy life, if environment is polluted/
What is meant by reforestation?
12.
Why should wild animals be protected?
7.
8.
9.
'
10.
54
Louis Pasteur
Charles Darwin
Dr. H. J. Bhabha
(1909 - 1966)
Scientist & Chairman of Atomic Energy Commission of India.
Awarded Padma Bhushan in 1954. Set up Atomic. Reactors
in Trombay near mumbai. Died in Air-crush.
Vegetables and Fruits
Rich in Vitamin-A
SUBHAS PUBLISHING HOUSE
No.l 16, 5th Main, 6th Cross, Chainarajpet,
Bangalore - 560 018
Rs. 3.55
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