Friend and Foe
Q42. Name the microorganisms which can fix atmospheric nitrogen
in the soil.
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?
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)?
Yeast is used for commercial production of alcohol, wine and acetic acid
Q45. Name some commonly known antibiotics which are made from
fungi and bacteria.
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?
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.
Common ailments like cold, influenza (flu) and most coughs are caused by
viruses. Serious diseases like polio and chicken pox are also caused by
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
Drink boiled drinking water.
Q50. How can food be preserved by adding oil and vinegar?
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
Q51. How milk is turned into curd?
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?
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?
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?
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
Maintain personal hygiene and good sanitary
Consume properly cooked food and boiled
Q57. What are pathogens?
are harmful in many ways. Some of the microorganisms cause diseases in human
beings, plants and animals. Such disease-causing microorganisms are called