Question 1: Fill in the blanks:
(a) Microorganisms can be seen with the help of a ____________.
(b) Blue-green algae fix __________ directly from the air to enhance the fertility of the soil.
(c) Alcohol is produced with the help of __________. (d) Cholera is caused by __________.
Answer:
(a) Microorganisms can be seen with the help of a microscope.
(b) Blue-green algae fix nitrogen directly from the air to enhance the fertility of the soil.
(c) Alcohol is produced with the help of microorganisms.
(d) Cholera is caused by bacteria.
Question 2: Tick the correct answer:
(a) Yeast is used in the production of (i) sugar (ii) alcohol (iii) hydrochloric acid (iv) Oxygen
(b) The following is an antibiotic (i) Sodium bicarbonate (ii) Streptomycin (iii) Alcohol (iv) Yeast
(c) Carrier of malaria-causing protozoan is (i) female Anopheles mosquito (ii) cockroach (iii) housefly (iv) butterfly
(d) The most common carrier of communicable diseases is (i) ant (ii) housefly (iii) dragonfly (iv) spider
(e) The bread or idli dough rises because of (i) heat (ii) grinding (iii) growth of yeast cells (iv) kneading
(f) The process of conversion of sugar into alcohol is called (i) nitrogen fixation (ii) moulding (iii) fermentation (iv) infection
Answer:
(a) Alcohol
(b) Streptomycin
(c) Female Anopheles mosquito
(d) Housefly
(e) Growth of yeast cells
(f) Fermentation
Question 3: Match the organisms in Column I with their action in Column II.
Column I Column II
(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
Answer:
(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
Question 4: Can microorganisms be seen with the naked eye? If not, how can they be seen?
Answer:
No, microorganisms cannot be seen by the naked eye because they are very small and are called microbes. They can be seen only with the help of a microscope.
Question 5: What are the major groups of microorganisms?
Answer:
Microorganisms are categorised into four major groups bacteria, fungi, protozoa and some algae. They have different sizes and modes of nutrition.
Bacteria–
They are small single-cell organisms having cell walls but no nucleus. They can be spherical, spiral or rod-shaped.
Fungi-
They are microorganisms containing a nucleus. They look like plants but cannot prepare their own food. They do not contain chlorophyll and cannot photosynthesise.
Protozoa–
They are animal-like microorganisms. Most of these are parasites and feed on other organisms.
Algae–
They are plant-like microorganisms. They contain chlorophyll and do photosynthesis to make food.
Question 6: Name the microorganisms which can fix atmospheric nitrogen in the soil.
Answer:
Bacteria such as rhizobium and some blue-green algae present in the soil can fix atmospheric nitrogen and convert it into usable nitrogenous compounds nitrates and nitrites, which are in turn used by plants for the synthesis of plant proteins and other compounds.
Question 7: Write 10 lines on the usefulness of microorganisms in our lives.
Answer:
Microorganisms are too small to be seen through the naked eye. However, they are vital to plants and the environment. Importance of microorganisms:
- They help in making curd, bread and cake. Milk is converted to curd by the multiplication of bacteria.
- Bacteria and yeast also help in the fermentation of rice idlis and dosa batter.
- Yeast is used for making bread, pastries and cakes.
- They clean up the environment. For example, breaking down organic waste into harmless and reusable substances by bacteria. They also increase soil fertility by fixing nitrogen.
Question 8:
Write a short paragraph on the harms caused by microorganisms.
Answer:
Microorganisms are harmful in many ways.
- Some cause diseases in humans, plants and animals. Such disease-causing microorganisms are called Pathogens.
- Some spoiled food, clothing and leather.
- Some microorganisms not only cause diseases in humans but also in animals. For example, anthrax is a dangerous human and cattle disease caused by a bacterium.
- Microorganisms also cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple and others causing reduced yield of crops.
Question 9:
What are antibiotics? What precautions must be taken while taking antibiotics?
Answer:
The medicines that kill or stop the growth of bacteria are called antibiotics.
They are effective only against bacterial infections. Examples: Streptomycin, tetracycline, penicillin etc.
The following precautions must be taken while taking antibiotics:
- Antibiotics should be taken only on a doctor’s prescription.
- One must complete the full course prescribed by the doctor.
- Antibiotics must be avoided when not needed or in the wrong doses.