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NCERT Solutions for Class 8th Science

 

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Chapter 2. Microorganisms : Friend And Foe

Additional Questions With Solutions

 

 

 

Additional Questions With Solutions


Q14: What is the role of nitrogen in living beings?

Ans: Nitrogen is used for the synthesis of amino acid, proteins and other nitrogenous molecules in the plants. When an animal take these plants as a food it get that proteins synthesise using nitrogen.

Q15: Why are antibiotics mixed with the feed of the livestock and poultry?

Ans: Antibiotics are mixed with the feed of the livestock and poultry to check microbial infection in animals.

Q16: What precautions must be taken while taking antibiotics?

Ans: Precautions are such as;

(i) Antibiotics should be taken only on the advised of a qualified doctor.

(ii) You must complete the course prescribed by the doctor.

Q17: What is communicable diseases?

Ans: Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases.

Q18: What is carriers?

Ans: There are some insects and animals which act as carriers of disease causing microbes like house fly and mosquito .

Q19: What is biological nitrogen fixer?

Ans: Some bacteria and blue green algae are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility. These microbes are commonly called biological nitrogen fixers.

Q20: What are pathogens?

Ans: Some of the cause diseases in humans beings, plants, and animals . Such disease causing microorganisms are called pathogens.

Q21: What is preservatives?

Ans: Salts and edible oils are the common chemicals generally used to check the growth of microorganisms. Therefore they are called preservatives.

Q22: What is pasteurization?

Ans: The milk is heated to about 70C for 15 to 30 seconds and then suddenly chilled and stored. By doing so, it prevents the growth of microbes. This process is called pasteurization.

Q23: Write the name of some preservatives.

Ans: Some preservatives are common salt ,sugar, oils, and Vinegar etc.

Q24: Name the factors which are responsible for fixation of nitrogen.

Ans: Rhizobium, blue green algae and some times through the action of lightning.

Q25: What do you understand by the fixation of nitrogen?

Ans: When Rhizobium and blue green algae present in the soil fix nitrogen from the atmosphere and convert it into compounds of nitrogen. Once nitrogen is converted into these usable compounds, it can be utilised by plants from the soil through their root system. This is known as fixation of nitrogen.

Q26: What is fixation of nitrogen?

Ans: The conversation of nitrogen into its compounds is known as fixation of nitrogen.

Q27: What is nitrogen cycle?

Ans: Nitrogen is one of the essential constituents of all living organism as a part of proteins. Nitrogen is used by the various organisms and they convert it into nitrogen compounds or nitrogenous wastes, these are reused by the plants. Some other bacteria converted it into nitrogen gas which goes back into the atmosphere. As percentage of nitrogen in the atmosphere is remains constant. This makes a cycle of nitrogen.

Q28: What is pasteurization?

Ans: Pasteurization is a method to preserve milk, in which the milk is heated to about 700C for 15 to 30 seconds and then suddenly chilled and stored. By doing so, it prevents the growth of microbes. This process was discovered by Louis Pasteur. It is called pasteurization.

 

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