- Fill in the blanks:
(a) Microorganisms can be seen with the help of a .
(b) Blue green algae fix directly from air to enhance fertility of soil.
(c) Alcohol is produced with the help of .
(d) Cholera is caused by .
- Tick the correct answer.
(a) Yeast is used in the production of
(iii) hydrochloric acid
(b) The following is an antibiotic
(i) Sodium bicarbonate
(c) Carrier of malaria-causing protozoan is
(i) female Anopheles mosquito
(d) The most common carrier of communicable diseases is
(e) The bread or idli dough rises because of
(iii) growth of yeast cells
(f) The process of conversion of sugar into alcohol is called
(i) nitrogen fixation
(a) (i) alcohol
(b) (ii) Streptomycin
(c) (i) female Anopheles mosquito
(d) (ii) housefly
(e) (iii) growth of yeast cells
(f) (iii) fermentation
- Match the organisms in column A with their action in Column B.
Column A Column B
(i) Bacteria (a) Fixing nitrogen
(ii) Rhizobium (b) setting of curd
(iii) Lactobacillus (c) Baking of bread
(iv) Yeast (d) Causing malaria
(v) A protozoan (e) Causing cholera
(vi) A virus (f) Causing AIDS
(g) Producing antibodies
Column A Column B
(i) Bacteria (a) Causing cholera
(ii) Rhizobium (b) Fixing nitrogen
(iii) Lactobacillus (c) setting of curd
(iv) Yeast (d) Baking of bread
(v) A protozoan (e) Causing malaria
(vi) A virus (f) Causing AIDS
- Can microorganisms be seen with the naked eye? If not, how can they be seen?
Microorganisms are very small to be seen through naked eyes. They can be seen with the
help of microscope or a magnifying glass.
For example, a fungus that grows on bread.
- What are the major groups of microorganisms?
There are five major groups of microorganisms:
(i) Bacteria – They are single celled disease-causing microorganisms. They can
be spiral or rod-shaped.
(ii) Fungi – They are mostly multicellular disease-causing microbes. Bread
moulds are common examples of fungi.
(iii) Protozoa -They mainly include organisms such as Amoeba, Plasmodium,
etc. They can be unicellular or multicellular.
(iv) Virus – Viruses are disease-causing microbes that reproduce only inside the
(v) Algae – They include multicellular, photosynthetic organisms such as
Spirogyra, Chlamydomonas, etc.
- Name the microorganisms which can fix atmospheric nitrogen in the soil.
Bacteria such as Rhizobium and certain blue-green algae present in the soil
can fix atmospheric nitrogen and convert it into usable nitrogenous compounds.
These nitrogenous compounds can be easily utilized by plants for the synthesis of
plant proteins and other compounds.
- Write 10 lines on the usefulness of microorganisms in our lives.
Microorganisms are too small to be seen through naked eyes. However, they
are useful to plants and the environment.
Importance of microorganisms:
i. They are used in winemaking, baking, pickling, and other food making
ii. Alcoholic fermentation by yeast is widely used in the preparation of wine
and bread. A bacterium Lactobacillus promotes the formation of curd.
iii. Yeast reproduces rapidly and produces carbon dioxide during respiration.
Bubbles of the gas fill the dough and increases its volume.
iv. Microbes are used to reduce pollution. For example, decomposers such as
bacteria and fungi break down dead bodies and excreta to form inorganic
compounds, which can be absorbed by plants.
v. They are used to increase the soil fertility by fixing the atmospheric nitrogen
with the help of bacterium Rhizobium and some other blue-green algae.
vi. Microbes also play an important role in the preparation of medicines.
vii. Antibiotics are chemicals produced by microorganisms to kill bacteria.
Streptomycin, for example, is an antibiotic.
viii. Certain microbes are also used in the biological treatment of sewage and
ix. Antibiotics are used to control many plant diseases.
x. Antibiotics are mixed with the feed of livestock and poultry to check
microbial infection in animals.
- Write a short paragraph on the harmful effects of microorganisms.
Harmful effects of microorganisms:
i. Many microorganisms cause diseases in animals which are called
pathogenic microorganisms. For example, in humans, bacteria cause
diseases such as tuberculosis, cholera, typhoid, etc.
ii. In cattle, the foot and mouth disease is caused by a virus.
iii. Also, several microbes cause diseases in plants. For example, the
productivity of wheat, orange, apple, etc. is reduced due to microbial
diseases in plants.
iv. Certain microbes, on entering into our body, produce toxic substances. This
leads to food poisoning. Some microorganisms such as fungus spoil our
food. For example, bread when left unused under moist conditions gets
spoilt by fungus, producing a white cotton-like growths on the bread.
- What are antibiotics? What precautions must be taken while taking antibiotics?
Antibiotics are medicines produced by certain microorganisms to kill other
disease-causing microorganisms. These medicines are commonly obtained from
bacteria and fungi. Streptomycin, tetracycline, penicillin, etc. are common
Precautions to be taken while using antibiotics are:
(i) Antibiotics should be taken under the supervision of a well-qualified doctor.
(ii) Course (intake) of antibiotics should be completed as per the prescription
given by the doctor.
(iii) Antibiotics should be taken in the right amount and at the right time. A
wrong dose of antibiotic makes the drug ineffective. Also, excessive
consumption of drugs may kill the useful bacteria present in our body.