Chapter 1: Microorganisms - Friends and Foe | Science Class 8th

Chapter 1: Microorganisms - Friends and Foe | Science Class 8th

Q 1. 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 _________.

Ans:

(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 Yeast .

(d) Cholera is caused by Bacteria.

Q2. Tick the correct Ans.

Ans.

(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) molding (iii) fermentation (iv) infection

Q3. Match the organisms in Column I with their action in Column II.

 Ans.

Column I	Column II
(i) Bacteria	(e) Causing cholera
(iii) Lactobacillus	(b) Setting of curd
(iv) Yeast	(c) Baking of bread
(v) A Protozoan	(d) Causing Malaria
(vi) A Virus	(f) Causing AIDS

---

Q4. Can microorganisms, be seen with the naked eye? If not, how can they be seen?

Ans: Microorganisms are too small to see with the naked eye. They are visible with the aid of a magnifying glass or microscope. For Example, Fungus that grows on bread is so small that it can only be seen with a magnifying glass or microscope.

Q5. What are the major groups of microorganisms?

Ans: There are five main types of Microbes:

• Bacteria: These are single-celled microorganisms that cause disease. They might have a rod or a spiral shape.
• Fungi: Most of these multicellular pathogenic microorganisms are fungi. Fungi commonly appear as bread mould.
• Protozoa: These creatures mostly consist of Amoeba, Plasmodium, etc. They could have one or many cells.
• Virus: Viruses are germs that cause disease and only reproduce inside their host organism.
• Algae: This class of organisms includes multicellular, photosynthetic species like Spirogyra, Chlamydomonas, etc.

Q6. Name the microorganisms which can fix atmospheric nitrogen in the soil.

Ans: Bacteria in the soil, such as Rhizobium and certain blue-green algae, can fix atmospheric nitrogen and convert it into usable nitrogenous compounds. Plants can easily utilise these nitrogenous compounds for the synthesis of plant proteins and other compounds.

Q7. Write 10 lines on the usefulness of microorganisms in our lives.

Ans: Microorganisms are too small for the human eye to see. However, they are essential to the ecosystem and plants. 

Importance of micro-organisms:

They are used in the production of wine, baking, pickling, and other foods. Yeast fermentation of alcohol is widely used in the production of wine and bread. Lactobacillus bacterium promotes curd formation.

Pollution is reduced by using microbes. Decomposers, such as bacteria and fungi, break down dead bodies and excreta to form inorganic compounds that plants can absorb.

They are used to boost soil fertility by fixing atmospheric nitrogen with the help of the Rhizobium bacterium and other blue-green algae.

Microbes also play an important role in the production of pharmaceuticals. Antibiotics are bacteria-killing chemicals produced by microorganisms. Streptomycin is an antibiotic, for example. Certain microbes are also used in biological sewage and industrial effluent treatment.

Q8. Write a short paragraph on the harms caused by microorganisms.

Ans: Microorganisms' harmful effects:

Microorganisms cause diseases in animals. Bacteria, for example, cause diseases such as tuberculosis, cholera, and typhoid in humans. Foot and mouth disease in cattle is caused by a virus. Several microbes also cause plant diseases. Microbial diseases in plants, for example, reduce wheat, orange, and apple productivity. When certain microbes enter our bodies, they produce toxic substances. This results in food poisoning. Some microorganisms, such as fungus, contaminate our food. For example, bread spoils when left unused in moist conditions, resulting in a white cotton-like growth on the bread.

Q9. What are antibiotics? What precautions must be taken while taking antibiotics?

Ans: Antibiotics are medicines that are produced by certain microorganisms in order to kill disease-causing microorganisms. These medications are frequently derived from bacteria and fungi. Common antibiotics include streptomycin, tetracycline, penicillin, and others.

Precautions to be taken while using antibiotics:

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 antibiotics makes the drug ineffective. Also, excessive consumption of drugs may kill the useful bacteria present in our body.