Here are the key points about each disease: Malaria - Protozoan parasite Plasmodium, transmitted by mosquito bites. Symptoms include fever, chills, flu-like illness. Prevention includes mosquito nets, repellents, spraying insecticides. Amoebic dysentery - Protozoan parasite Entamoeba histolytica, transmitted through contaminated food or water. Symptoms include bloody diarrhea, stomach cramps. Prevention includes proper sanitation, boiling drinking water, hand washing. Measles - Virus transmitted through airborne droplets from coughs or sneezes. Symptoms include high fever, runny nose, cough, red rash. Prevention includes vaccination.

1. MICROORGANISMs:
FRIENDS AND FOE

2. Microorganisms are present all
around us but they are too small
to be seen with naked eye.
They are present everywhere in
the atmosphere(air, water and
soil)
INTRODUCTION

3. MICROORGANISMS (MICROBES) :-
•Microorganisms are very small organisms which cannot be seen with the unaided eye.
They can be seen only with a microscope.
•Microorganisms may be unicellular or multicellular.
•Microorganisms may exist alone or in colonies.
for example , you mighty observed that during the rainy seasons moist bread gets
spoilt and its surface gets covered with greenish-white patches.

4. TYPES OF MICROORGANISMS :-
•There are four main types of microorganisms. They are :-
bacteria, fungi, algae and protozoans.
• for example:-
Bacteria – lactobaccilus, E.Coli etc.
Algae – Chlamydomonas, Spirogyra etc.
Fungi – Bread mould, Penicillium, Aspergilles etc.
Protozoans – Amoeba, Paramaecium etc.
• Viruses are also considered as microorganisms. They are
different from other microorganisms because they reproduce
only in the body of host organisms like bacteria, plants or
animals.
•Common ailments like cold, influenza(flu) and most coughs are
caused by viruses. Serious diseases like polio and chicken pox
are also caused by viruses.

5. Bacteria
Spiral bacteria Rod-shaped bacteria
Algae
Chlamydomonas Spirogyra
Protozoa
Amoeba Paramecium
Fungi
Bread Mould Penicillium Aspergillus

6. VIRUS

7. Microorganisms play an important role in our lives. Some of them
are beneficial in many ways whereas some others are harmful and
cause diseases.
Microorganisms are used for making curd from milk, for making
cheese, pickles, bread, cakes, pastries, alcohol, wine, vinegar (acetic
acid) etc.
a) Making curd from milk :- The bacterium called Lactobacillus
reproduces in milk and helps to convert milk into curd.
b) Making bread :- The fungus called yeast reproduces in flour
dough and produces carbon dioxide during respiration which makes
the dough soft and helps in making bread, cakes, biscuits, pastries
etc.

8.  Microorganisms are used for the large scale
production of alcohol, wine and acetic acid
(vinegar). Yeast is used for commercial
production of alcohol and wine. For this
purpose yeast is grown on natural sugars
present in grains like barley, wheat, rice and
crushed fruit juices, etc.
 The process of conversion of sugar into
alcohol is known as fermentation.
 Louis Pasteur discovered fermentation in
1857.

9.  Whenever you fall ill the doctor may give you some antibiotic
tablets, capsules or injections such as of penicillin.
 The source of these medicines is microorganisms.
 Such medicines are called antibiotics. These days a number of
antibiotics are being produced from bacteria and fungi.
Streptomycin, tetracycline and erythromycin are some of the
commonly known antibiotics.
 These medicines kill or stop the growth of the disease-causing
microorganisms.

10.  It is important to remember that antibiotics should be
taken only on the advice of a qualified doctor.
 Also you must finish the course prescribed by the doctor.
If you take antibiotics when not needed or in wrong
doses, it may make the drug less effective when you
might need it in future.
 Also antibiotics taken unnecessarily may kill the
beneficial bacteria in the body.
 Antibiotics, however, are not effective against cold
and flu as these are caused by viruses.

11.  In 1929, Alexander Fleming was
working on a culture of disease
causing bacteria.
 Suddenly he found the spores of a
little green mould in one of his culture
plates.
 He observed that the presence of
mould prevented the growth of
bacteria. In fact, it also killed many of
these bacteria. From this the mould
penicillin was prepared.

12.  When a disease-carrying microbe enters our body, the body produces
antibodies to fight the invader. The body also remembers how to fight
the microbe if it enters again. So, if dead or weakened microbes are
introduced in a healthy body, the body fights and kills them by
producing suitable antibodies. The antibodies remain in the body and
we are protected from the disease causing microbes. This is how a
vaccine works. Several diseases, including cholera, tuberculosis,
smallpox and hepatitis can be prevented by vaccination.
 Children are given injections to protect themselves against several
diseases. Necessary vaccines are available in hospitals.
 Vaccinations are given to children for protection against polio under
Pulse Polio Program. Polio drops given to children are actually a
vaccine. This is called Oral vaccination.
 These days vaccines are made on a large scale from microorganisms
to protect humans and other animals from several diseases.

13.  Some bacteria and blue green algae are
able to fix nitrogen from the atmosphere
to enrich soil with nitrogen and increase
its fertility. These microbes are commonly
called biological nitrogen fixers.

14.  You often see large amounts of dead organic
matter in the form of decaying plants and
sometimes dead animals on the ground. You find
that they disappear after some time. This is
because the microorganisms decompose dead
organic waste of plants and animals converting
them into simple substances.
 These substances are again used by other plants
and animals. Thus, microorganisms can be used
to degrade the harmful and smelly substances
and thereby clean up the environment.

15.  Microorganisms are harmful in many ways. Some of the microorganisms
cause diseases in human beings, plants and animals. Such disease-causing
microorganisms are called pathogens.
 Pathogens enter our body through the air we breathe, the water we drink or
the food we eat. They can also get transmitted by direct contact with an
infected person or carried through an animal.
 Microbial diseases that can spread from an infected person to a healthy
person through air, water, food or physical contact are called communicable
diseases.
Examples of such diseases include cholera, common cold, chicken pox and
tuberculosis.
 When a person suffering from common cold sneezes, fine droplets of moisture
carrying thousands of viruses are spread in the air. The virus may enter the
body of a healthy person while breathing.

16. • There are some insects and animals which act as carriers of
disease-causing microbes.
• Housefly is one such carrier.
• The flies sit on the garbage and animal excreta. Pathogens stick to
their bodies. When these flies sit on uncovered food they may
transfer the pathogens. Whoever eats the contaminated food is
likely to get sick.
• Mosquito is another carrier.
• Examples of carriers are: the female Anopheles
mosquito which carries the parasite of malaria;
 Female Aedes mosquito acts as carrier of dengue virus.
• All mosquitoes breed in water. Hence, one should not let
water collect anywhere, in coolers, tyres, flower pot etc.
By keeping the surroundings clean and dry we can
prevent mosquitoes from breeding.

17. Human
Disease
Causative
Microorganis
ms
Mode of
Transmissi
on
Preventive Measures
(General)
Tuberculos
is
Measles
Chicken
Pox
Polio
Bacteria
Virus
Virus
Virus
Air
Air
Air/Contact
Air/Water
Keep the patient in complete
isolation. Keep the personal
belongings of the patient away
from those of others.
Vaccinations to be given at
suitable age
Cholera
Typhoid
Bacteria
Bacteria
Water/Food
Water
Maintain personal hygiene and
good sanitary habits. Consume
properly cooked food and
boiled drinking water.
Vaccination
Hepatitis A Virus Water Drink boiled drinking water.
Vaccination.
Malaria Protozoa Mosquito Use mosquito net and
repellents. Spray insecticides
and control breeding of

18.  Several microorganisms not only cause diseases
in humans and plants, but also in other animals.
For example, anthrax is a dangerous human and
cattle disease caused by a bacterium. Foot and
mouth disease of cattle is caused by a virus.
 Robert Köch (1876) discovered the bacterium
(Bacillus anthracis) which causes anthrax
disease.

19.  Several microorganisms cause diseases in plants like wheat,
rice, potato, sugarcane, orange, apple and others. The
diseases reduce the yield of crops. They can be controlled by
the use of certain chemicals which kill the microbes.

20. Plant Disease
Microorganis
m
Mode of
Transmissi
on
Figure
Citrus
canker
Bacteria Air
Rust of
wheat
Fungi Air,
seeds
Yellow vein
mosaic of
bhindi (Okra)
Virus Insect

21. Food preservation
Food is spoilt by microorganisms. Spoilt food has bad smell and bad taste and
causes food poisoning. Food can be preserved by protecting it from
microorganisms.
Food can be preserved by different methods. They are :-
i)Chemical method :- Food like pickles can be preserved by using chemicals like
salts and edible oils. Jams and squashes can be preserved by using sodium
benzoate, sodium metabisulphite. These chemicals are called preservatives.
ii) By using common salt :- Food items like fish, meat, amla, raw mangoes,
tamarind etc can be preserved by using common salt. It prevents the growth of
microbes.
iii) By using sugar :- Food items like jams, jellies, squashes etc. can be preserved
by using sugar solution. It prevents the growth of microbes.
iv) By using oil and vinegar :- Food items like pickles, vegetables, fish, meat etc.
are preserved by using oil and vinegar. It prevents the growth of microbes.
v) By heat and cold treatments :- Heating food items kills microbes. Similarly
storing food items at low temperatures prevents growth of microbes.

22. Pasteurization :- The process of heating milk to about 70oC for 15 to 30
seconds and then suddenly chilling it to prevent the growth of microbes is
called pasteurization. This process was discovered by Louis Pasteur.
vi) By storage and packing :- Many food items are stored in air tight
containers to protect them from microbes.

23. Nitrogen cycle
ATMOSPHERIC
NITROGEN
LIGHTNING FIXES
NITROGEN
NITROGEN FIXING BACTERIA
AND BLUE GREEN ALGAE
FIX ATMOSPHERIC NITROGEN
COMPOUNDS OF
NITROGEN IN THE SOIL
UPTAKE BY
PLANTS
ANIMAL EATS
PLANTS
NITROGENOUS
WASTE FROM
EXCRETION
AND DEATH
BACTERIA TURN
COMPOUNDS OF
NITROGEN INTO
GASEOUS NITROGEN

24. Nitrogen cycle
•The nitrogen in the atmosphere is converted into nitrogen compounds in the
soil by nitrogen fixing bacteria and blue green algae.
•Lightning also converted into nitrogen compounds in the soil.
•The nitrogen compounds in the soil is used by plants for the synthesis of
proteins and other compounds.
•Animals feeding on plants get these proteins and other compounds.
•When plants and animals die, bacteria and fungi in the soil converts the
nitrogenous waste into nitrogen compounds in the soil which are again use
by plants.
•Some other bacteria converts some nitrogen compounds in the soil into
nitrogen gas which goes back into the atmosphere. Hence the nitrogen in the
atmosphere almost remains constant.

25.  Take some soil in a glass container. Fill it with
tap water. Keep it exposed to sunlight. After few
days, you will see growth of green layer on the
surface of the container. Observe it using
magnifying glass.
a) what do you see?
b)Name the microorganism.

26.  Take ½ kg flour (atta or maida ),add some sugar
and mix with warm water. Add a small amount of
yeast powder and knead to make a soft dough.
a) What do you observe after two hours?
b)Did you find the dough rising?

27.  Take a 500 ml beaker filled up to ¾ with water.
Dissolve 2-3 tea spoons of sugar in it. Add half a
spoon of yeast powder to the sugar solution.
Keep it covered in a warm place for 4-5 hours.
Now smell the solution.
a) Could you get a smell?
b) What type of smell it is?

28.  Take two pots and fill each pot half with soil.
Mark them A and B. Put plant waste in pot A and
things like polythene bags, empty glass bottles
and broken plastic toys in pot B. Put the pots
aside. Observe them after 3-4 weeks.
Do you find any difference in the contents of the
two pots? If so, what is the difference?

29. 1. Why do you think?
i) Curd sets faster in summer than in winters?
ii) Curd turns sour faster in summer than in winter?
2. The sealed packets in which food items such as chips are sold are usually filled with nitrogen.
How do you think that helps?
3. Why should you always wash your hands before handling food and after going to the toilet?
4. Evolution i.e. changes in an organisms to adjust to the environment, as suggested by Charles
Darwin, is a very slow process that takes place over tens of thousands of generations, taking
millions of years. However, in bacteria, developing resistance to antibiotics, which is a type of
evolution, takes place within our own lifetime. Can you say why it occurs so quickly in
bacteria?
5. Why are protozoa known as an important link for aquatic food chains?
6. Most of the preservatives are chemicals still we use them in our food to preserve. Why?
7. After consuming a dish of mutton, a person complained of nausea, vomiting, diarrhea and pain
in the abdomen.
(i) What type of disease is he suffering from?
(ii) What causes this disease.
8. Why do dry food items such as biscuits not spoil easily?

30. 1. GIVE REASON FOR THE FOLLOWING:
a) Antibiotics are not useful in treatment of viral infections.
b) Milk is stored in refrigerator during summers.
c) Are all microorganisms harmful?
d) Algae are plant-like while protozoa are animal-like microorganisms.
e) Yeast is used in bakeries and breweries.
2. Differentiate between communicable and non- communicable diseases
3. SHORT ANSWER TYPE QUESTIONS:
a) How are viruses different from other microbes?
b) Mention the role of nitrogen- fixing bacteria in soil.
c) How do microorganisms help in cleaning the environment?
d) What are antibiotics? What precautions must be taken while taking antibiotics?
4. LONG ANSWER TYPE QUESTION:
a)Why bacteria are regarded as our foes and friend?
b) Mention the ways in which the following micro- organisms are harmful to mankind:
Bacteria, protozoa and viruses.
c)What is fermentation? Discuss its uses in making alcoholic beverages.

31. DISEASE CAUSE SYMPTOMS PREVENTION
Malaria
Amoebic dysentery
Measles
TB
Hepatitis B