Chapter 2: Micro-organisms: Friend and Foe
Exercises (Page 29)
1. Fill in the blanks.
(a) Micro-organisms can be seen with the help of a microscope.
(b) Blue green algae fix nitrogen directly from air to enhance fertility of soil.
(c) Alcohol is produced with the help of yeast.
(d) Cholera is caused by bacteria.
2. Tick the correct answer.
(a) Yeast is used in the production of — alcohol.
(b) The following is an antibiotic — Streptomycin.
(c) Carrier of malaria-causing protozoan is — female Anopheles mosquito.
(d) The most common carrier of communicable diseases is — housefly.
(e) The bread or idli dough rises because of — growth of yeast cells.
(f) The process of conversion of sugar into alcohol is called — fermentation.
3. Match the organisms in Column A with their action in Column B.
(i) Bacteria — (e) Causing cholera.
(ii) Rhizobium — (a) Fixing nitrogen.
(iii) Lactobacillus — (b) Setting of curd.
(iv) Yeast — (c) Baking of bread.
(v) A protozoan — (d) Causing malaria.
(vi) A virus — (f) Causing AIDS.
4. Can micro-organisms be seen with the naked eye? If not, how can they be seen?
Answer. No, micro-organisms cannot be seen with the unaided eye because they are so small in size.
They can be seen using a microscope. Some, such as the fungus that grows on bread, can be seen with a magnifying glass.
5. What are the major groups of micro-organisms?
Answer. The four major groups are bacteria, fungi, protozoa, and some algae.
6. Name the micro-organisms which can fix atmospheric nitrogen in the soil.
Answer. Bacteria like Rhizobium and certain blue-green algae are able to fix nitrogen from the atmosphere.
7. Write 10 lines on the usefulness of micro-organisms in our lives.
Answer. a)They are used in the preparation of curd, bread, and cake.
b) They have been used for the production of alcohol and wine for ages.
c)They help in cleaning the environment by breaking down organic wastes into harmless substances.
d)They are used in the preparation of medicines like antibiotics.
e)They increase soil fertility by fixing atmospheric nitrogen.
f)Bacteria like Lactobacillus help in converting milk into curd.
g)Yeast is essential in the baking industry for making pastries and cakes because it releases carbon dioxide, making dough rise.
h)They are used in making cheese, pickles, and other food items.
i)Vaccines are made from micro-organisms to protect humans and animals from diseases.
j)Some microbes decompose dead organic matter into simple nutrients that plants can reuse.
8. Write a short paragraph on the harms caused by micro-organisms.
Answer. Micro-organisms called pathogens cause diseases in humans, plants, and animals. In humans, they cause ailments like cholera, tuberculosis, and malaria. They also cause diseases in livestock, such as anthrax and foot and mouth disease. In plants, they can reduce crop yield by causing diseases like citrus canker or rust of wheat. Additionally, some micro-organisms spoil food, clothing, and leather items. Food poisoning is caused by microbes growing on food and producing toxic substances.
9. What are antibiotics? What precautions must be taken while taking antibiotics?
Answer. Antibiotics are medicines produced from micro-organisms (like bacteria and fungi) that kill or stop the growth of disease-causing microbes.
Precautions:
They should be taken only on the advice of a qualified doctor.
One must complete the full course prescribed by the doctor.
They should not be taken unnecessarily or in wrong doses, as this may make the drug less effective in the future and kill beneficial bacteria in the body.
They are not effective against cold and flu since these are caused by viruses.