the chapter is about microorganisms of eighth std.

2. Organisms that are so small that they can only be seen through a
microscope are called microorganisms or microbes.

3. Bacteria
Algae
Protozoa
Virus
Fungi

4. Bacteria are found in three different shapes:
 rod shaped , called bacilli
 Spherical , called cocci
 Spiral , called spirilla

5. CHARACTERISTICS OF ALGAE:
 Algae are eukaryotic organisms
 Mostly photosynthetic
They are almost marine ,
very few are freshwater.
Algae can be unicellular
or multicellular.
Algae reproduce either
by vegetative , asexual
or sexual methods.

6. Characteristics of protozoa:
 Protozoa are unicellular
Organisms that have animal
like characteristics.
They are eukaryotic
microorganisms.
They can move from place
to place.
 Some protozoa live in fresh or salty water
while others live in soil.

7. Characteristics of fungi:
o Fungi are plant like organisms that do not
contain chlorophyll.
o They may be unicellular or multicellular.
o They grow best in dark , warm and moist
places.

8. Characteristics of
viruses:
 Viruses can
replicate only by
infecting a host cell.
 They cannot
reproduce on their
own.
 They infect a wide
variety of organisms
, including both
eukaryotes and
prokaryotes.

10. In food and beverage industry
• Lactobacillus is a bacterium that sours milk and is used to prepare
curd from
milk.
• Fungi like mushrooms and morels are edible and are rich source of protein.
• Yeast is used in preparing food items like bread and cakes.
(Activity-2.3 Dough making using yeast and flour)
• Yeast is also used in breweries for making alcohol, wines and acetic acid
(commercial use) by the process of fermentation (conversion of sugar into
alcohol). Yeast is grown on natural sugars present in grains like barley,
wheat, rice, crushed fruit juices, etc.
(Activity-2.4 Alcohol preparation using sugar solution and yeast)
Louis Pasteur discovered fermentation in 1857
Beneficial Microorganisms

11. • Some bacteria (Rhizobium) and blue green algae (Nostoc) live in the root
nodules of plants such as gram, pea (leguminous plants) etc. These
bacteria absorb the nitrogen from the atmosphere and convert it into nitrate
which serves as natural fertilizers for plants, hence, enhancing soil fertility.
• These microbes are commonly called as biological nitrogen fixers.
In agriculture

12. The alcohol as sugar has been
converted into alcohol by yeast. This
process of conversion of sugar into
alcohol is known as FERMENTATION.

13. • 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.
• The plant waste can be converted into manure by the action of microbes.
The nutrients released in the process can be used by the plants again.
(Activity-2.5 Making manure using plant waste, fruit and vegetable
peels vs. plastic waste, e-waste)
In cleaning the environment

14. • 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.
• Diseases like cholera, tuberculosis, smallpox and hepatitis can be
prevented by vaccination.
In making medicines - vaccines

15. • Antibiotics are medicines which kill or stop the growth of the disease-
causing microorganisms.
• A number of antibiotics are being produced from bacteria and fungi.
Ex: Streptomycin, tetracycline, erythromycin
• Antibiotics are mixed with the feed of livestock and poultry to check microbial
infection in animals.
• They are also used to control many plant diseases.
• Antibiotics are not effective against cold and flu as these are caused by
viruses.
Note: Antibiotics should be taken only on the advice of a qualified doctor and
the prescribed course should be completed.
In making medicines-antibiotics

16. Some of the microorganisms cause diseases in human beings, plants and
animals. Such disease-causing microorganisms are called pathogens.
Harmful microorganisms
In Humans
• Pathogens enter our body through the air we breathe, the water we drink or
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. Ex: common cold, chicken pox, tuberculosis.

18. [1] Anthrax
Host: Humans, cattle
Pathogen: bacteria (Bacillus . anthracis )
[1] Foot and mouth disease
Host: cattle
Pathogen: virus Foot-and-mouth disease virus (FMDV)
In Animals

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

20. • Microorganisms spoil our food.
• Spoiled food emits bad smell and has a bad taste and colour change.
• Spoiling of food is a chemical reaction
• Food poisoning could be due to the consumption of food spoilt by some
microorganisms.
• Microorganisms that grow on food sometimes produce toxic substances.
These make the food poisonous causing serious illness and even death.
food poisoning

21. Food preservation
• Processing of food to prevent their spoilage and to retain their nutritive value
for longer period is called food preservation.
• Preservatives: The common chemicals generally used to prevent the
growth of microorganisms. Ex: salt, sugar, edible oil, acids, etc.
• Food can be preserved using many methods:
1. Chemical method
Standard preservatives (recognized safe by national food agencies)
Salt
Sugar
Oil and Vinegar
2. Heat and cold treatments
Pasteurization
3. Storage and packing

22. Pasteurised milk can be consumed without boiling as it is free from harmful
microbes.
Milk is heated to about 70°C for 15 to 30 seconds and then suddenly
chilled and stored. This process prevents the growth of microbes.
Pasteurisation
Discovery: Louis Pasteur - Pasteurisation.

23. • Rhizobium is involved in the fixation of nitrogen in leguminous plants. It
lives
in the root nodules of leguminous plants such as beans and peas, with
which it has a symbiotic relationship.
• Nitrogen also gets fixed through the action of lightning.
• The amount of nitrogen in the atmosphere remains constant.
• Our atmosphere has 78% nitrogen gas.
Nitrogen Fixation

25. Mindmap