Microorganisms: Friend and Foe

Q79. Explain nitrogen cycle.

Ans. Our atmosphere has 78% nitrogen gas. The atmospheric nitrogen cannot be taken directly by plants and animals. Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert 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. Nitrogen is then used for the synthesis of plant proteins and other compounds. Animals feeding on plants get these proteins and other nitrogen compounds. When plants and animals die, bacteria and fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds to be used by plants again. Certain other bacteria convert some part of them to nitrogen gas which goes back into the atmosphere. As a result, the percentage of nitrogen in the atmosphere remains more or less constant.

Q80. What are the different methods of food preservation?

Ans. Different methods of food preservation are:

Chemical Method - Salts and edible oils are the common chemicals generally used to check the growth of microorganisms.

Preservation by Common Salt - Common salt has been used to preserve meat and fish for ages. Salting is also used to preserve amla, raw mangoes, tamarind, etc.

Preservation by Sugar - Jams, jellies and squashes are preserved by sugar.

Preservation by Oil and Vinegar - Use of oil and vinegar prevents spoilage of pickles because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.

Heat and Cold Treatments – This process kills many microorganisms. Milk is boiled before it is stored or used.

Storage and Packing - Dry fruits and even vegetables are sold in sealed air tight packets to prevent the attack of microbes.

Q81. Complete the table.

Q82. Draw diagrams of Chlamydomonas, Spirogyra, Amoeba, Paramecium, Bread mould, Penicillium and Aspergillus.

Ans.

Chlamydomonas

 Spirogyra     

Amoeba

Paramecium

Bread mould

Penicillium

Aspergillus