NCERT Solutions for Class 8 Science Chapter 2 Microorganisms Friend and Foe

Ans : (a) Microorganisms 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  

Ans : (a) — (ii)
(b) — (ii)
(c) — (i)
(d) — (ii)
(e) — (iii)
(f) — (iii) 

Ans : Micro-organisms are too small to be seen through naked eyes. They can be seen with the help of a magnifying glass or microscope. 
For example, fungus that grows on bread is so small that it can be seen only with the help of a magnifying glass or microscope. 

Ans : There are five major groups of micro-organisms: 
(i) Bacteria — They are single celled disease-causing micro-organisms. 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 host organism. 
(v) Algae — They include multicellular, photosynthetic organisms such as Spirogyra, 
Chlamydomonas, etc. 

Ans : 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.