Topic outline

    • Microorganisms: Friend and Foe

      Q42. Name the microorganisms which can fix atmospheric nitrogen in the soil.

      Ans. Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert into compounds of nitrogen.


      Q43. Why sugar is used as preservative?

      Ans. Sugar is used as preservative in jams, jellies and squashes. Sugar reduces the moisture content which inhibits the growth of bacteria which spoil food.


      Q44. Which microorganism is used for commercial production of alcohol, wine and acetic acid (vinegar)?

      Ans. Yeast is used for commercial production of alcohol, wine and acetic acid (vinegar).

      Q45. Name some commonly known antibiotics which are made from fungi and bacteria.

      Ans. Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria.


      Q46. What are the harmful effects of microorganisms on plants?

      Ans. Several microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple and others. The diseases reduce the yield of crops.


      Q47. Name some diseases caused by virus.

      Ans. Common ailments like cold, influenza (flu) and most coughs are caused by viruses. Serious diseases like polio and chicken pox are also caused by viruses.


      Q48. How does food become poisonous?

      Ans. Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death.


      Q49. How can we prevent the spread of hepatitis B?

      Ans. Ways to prevent the spread of hepatitis B

                               i.        Drink boiled drinking water.

                              ii.        Vaccination

      Q50. How can food be preserved by adding oil and vinegar?

      Ans. Use of oil and vinegar prevents spoilage of food because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.


      Q51. How milk is turned into curd?

      Ans. A little curd is added to warm milk to set curd. Curd contains several microorganisms. Of these, the bacterium Lactobacillus promotes the formation of curd. It multiplies in milk and converts it into curd.


      Q52. How does common cold spread?

      Ans. When a person suffering from common cold sneezes, fine droplets of moisture carrying thousands of viruses are spread in the air. The virus may enter the body of a healthy person while breathing.


      Q53. Why is tuberculosis considered as infectious disease?

      Ans. Tuberculosis is considered as infectious disease because bacteria that cause tuberculosis are spread from one person to another through tiny droplets released into the air via coughs and sneezes.


      Q54. What causes tuberculosis and how is it spread?

      Ans. Tuberculosis is caused by bacteria that spread from person to person through microscopic droplets released into the air. This can happen when someone with tuberculosis coughs, speaks, sneezes or spits.

      Q55. What are biological nitrogen fixers?

      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.


      Q56. How can cholera be prevented?

      Ans. Prevention of cholera

                               i.        Maintain personal hygiene and good sanitary habits.

                              ii.        Consume properly cooked food and boiled drinking water.

                             iii.        Vaccination.


      Q57. What are pathogens?

      Ans. Microorganisms are harmful in many ways. Some of the microorganisms cause diseases in human beings, plants and animals. Such disease-causing microorganisms are called pathogens.