Friend and Foe
Q58. How do pathogens enter our body?
Pathogens enter our body through the air we breathe, the water we drink or the
food we eat. They can also get transmitted by direct contact with an infected
person or carried through an animal.
Q59. Why should we keep our food covered?
Ans. Flies sit on uncovered food and they may transfer
the pathogens. Whoever eats the contaminated food is likely to get sick. So, it
is advisable to always keep food covered.
Q60. Why should we not let water collect anywhere in the
mosquitoes breed in water. Hence, one should not let water collect anywhere, in
coolers, tyres, flower pot etc. By keeping the surroundings clean and dry we
can prevent mosquitoes from breeding.
Q61. Name the bacterium found in the roots of pea plant. How is
this bacterium useful?
Ans. Rhizobium lives in the root nodules of leguminous
plants such as beans and peas. It is involved in the fixation of nitrogen in leguminous
Q62. Why are viruses considered to be on the borderline between
living organisms and non-living things?
Ans. Viruses are also microscopic. They, however, reproduce
only inside the cells of the host organism, which may be a bacterium, plant or
Q63. What will happen if we take antibiotics when not needed?
Ans. If we take antibiotics when not needed or in wrong
doses, it may make the drug less effective when we might need it in future.
Also antibiotics taken unnecessarily may kill the beneficial bacteria in the
Q64. What are carriers of disease causing microbes? Give
There are some insects and animals which act as carriers of disease causing microbes.
Housefly is one such carrier. Another example of a carrier is the female
Anopheles mosquito, which carries the parasite of malaria.
Q65. What happens when yeast powder is added to sugar solution
and kept for 4-5 hours?
Ans. When yeast powder is added to sugar solution
kept for 4-5 hours, fermentation takes place. Sugar has been converted into
alcohol by yeast. This process of conversion of sugar into alcohol is known as
Q66. Write some common uses of yeast.
uses of yeast are:
It is used in the baking industry for
making breads, pastries and cakes.
It is used for commercial production of
alcohol and wine.
Q67. Why is yeast used in baking industry?
Ans. Yeast reproduces rapidly and produces carbon
dioxide during respiration. Bubbles of the gas fill the dough and increase its
volume. This is the basis of the use of yeast in the baking industry for making
breads, pastries and cakes.
Q68. How do houseflies spread disease?
Housefly is one such carrier. The flies sit on the garbage and animal excreta.
Pathogens stick to their bodies. When these flies sit on uncovered food they
may transfer the pathogens. Whoever eats the contaminated food is likely to get
Q69. Write a short paragraph on the harms caused by
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. Some microorganisms spoil food, clothing and leather.
Q70. What is called pasteurization?
Ans. It is a process in which 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.