Topic outline

    • Microorganisms: Friend and Foe

      Q71. What are communicable diseases? Give examples.

      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. Examples of such diseases include cholera, common cold, chicken pox and tuberculosis.


      Q72. Can microorganisms be seen with the naked eye? If not, how can they be seen?

      Ans. Microorganisms or microbes are so small in size that they cannot be seen with the unaided eye. Some of these, such as the fungus that grows on bread, can be seen with a magnifying glass. Others cannot be seen without the help of a microscope.

      Q73. Where do microorganisms live?

      Ans. They can survive under all types of environment, ranging from ice cold climate to hot springs and deserts to marshy lands. They are also found inside the bodies of animals including humans. Some microorganisms grow on other organisms while others exist freely. Microorganisms like amoeba can live alone, while fungi and bacteria may live in colonies.


      Q74. Why is curd an important ingredient in making rava idlis and bhaturas?

      Ans. Curd is added while making idli and bhatura dough as curd contains Lactobacillus bacteria that undergoes anaerobic respiration and in this process it acts on sugar of the flour and releases carbon dioxide gas, this gas make the dough rise and when baked or fried gas escapes leaving the idli or bhatura soft and spongy.


      Q75. How a vaccine works?

      Ans. When a disease-carrying microbe enters our body, the body produces antibodies to fight the invader. The body also remembers how to fight the microbe if it enters again. So, if dead or weakened microbes are introduced in a healthy body, the body fights and kills them by producing suitable antibodies. The antibodies remain in the body and we are protected from the disease causing microbes. This is how a vaccine works.

      Q76. Mention some important uses of fungi.

      Ans. Uses of fungi

                                i.        Some antibiotics are made from fungi.

                               ii.        When plants and animals die fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds to be used by plants again.

                              iii.        Yeasts are single-celled fungi. It is used in baking industry for making breads, pastries and cakes and for commercial production of alcohol and wine.


      Q77. Write 10 lines on the usefulness of microorganisms in our lives.

      Ans. Microorganisms play an important role in our lives. Some of them are beneficial in many ways.

                                i.        They are used in the preparation of curd, bread and cake.

                               ii.        They are used for the large scale production of alcohol, wine and acetic acid (vinegar).

                              iii.        They are also used in cleaning up of the environment. For example, the organic wastes (vegetable peels, remains of animals, faeces, etc.) are broken down into harmless and usable substances by bacteria.

                              iv.        Bacteria are also used in the preparation of medicines.

                               v.        In agriculture they are used to increase soil fertility by fixing nitrogen.

      Q78. What are antibiotics? What precautions must be taken while taking antibiotics?

      Ans. Antibiotics are the medicines prepared from microorganisms to kill or stop the growth of the disease-causing microorganisms.

      Precautions to be taken while taking antibiotics:

                              i.        Antibiotics should be taken only on the advice of a qualified doctor.

                             ii.        Course of antibiotics should be completed as prescribed by the doctor.

                            iii.        Antibiotics should be taken in the right amount and at the right time. If antibiotics are taken unnecessarily it may kill the beneficial bacteria in the body.

                            iv.        Antibiotics are not effective against cold and flu as these are caused by viruses.