8th Class Science Microorganisms : Friend and Foe Introduction

         Introduction

Microorganisms are the organisms, which are very small and cannot be seen, except with the help of microscope. They are found everywhere on the earth in air, water and land. There are different groups of microorganisms, that is, bacteria, fungi, protozoa and viruses.

Microorganisms was first observed in 1674, by Van Leeuwenhoek. Although these organisms are very small, but they play very significant role to keep the life going on earth. They carry out 90% of the biochemical reactions on the earth surface, and in the atmosphere. It is believed, perhaps they are the first life forms on the earth that might have appeared. Hence they are the most common ancestors of all living being on the earth. They might have appeared 3.8 billion years ago. The first ever microorganism, that would have exist was bacilli. The discovery of the microorganisms has changed the human perception about the world. The different microorganisms are:

(i) Protozoa                         

(ii)  Fungi

(iii) Bacteria                      

(iv) Viruses

           Protozoa

These are the single cellular microorganisms, which have been classified as animals. They are found in ponds, lakes, drains, rivers and sea water. For example, amoeba, paramecium and entamoeba. They are parasitic in nature and causes disease like malaria and dysentery. Plasmodium is the parasite of the malaria. It is classified into four groups, on the basis of mode of locomotion or the cell organization, Protozoa's

             Fungi

These are the large group of organisms, which do not have chlorophyll and depend on other for their food. They cannot manufacture their own food by the process of photosynthesis. For example, yeast, moulds, penicillium and aspergillus. They need warm and moist condition for their growth. They are normally saprophytes, which feed on dead decaying matters. But some of them are parasitic in nature and cause disease. Some of the disease caused by fungi are ringworm and athlete foot.

The microscope fungi are eukaryotic cells and are used for the production of alcoholic drinks. They are also used for research in the field of biomedical and biotechnology.

                                                      Fungi

           Bacteria

The bacteria are the single cellular organisms, which are very small, having cell wall and with no defined nucleus. They are found everywhere on the earth. There are mainly three groups of bacteria, depending on their shape, that is, spherical, rod and spiral shape. The most common bacteria are lactobacillus, rhizobium, bacilli and cocci. They reproduce by binary fission and grow very rapidly in favorable conditions. Some bacteria are useful in making food like curds and other help in nitrogen fixation and decomposing the organic waste. Some of the disease caused by the bacteria is cholera, typhoid, TB, diphtheria and food poisoning. However, they can also reproduce sexually, in which they exchange genetic information through DNA. They can even live under extreme conditions.

                                         Bacteria

           Viruses

These are the smallest microorganisms, which can develop inside the body of host organisms. They behave like both living and nonliving. When they enter the body of host organisms, they behave like living and in outside they behave like non living organisms. Thus, they are said to be on the border line of living and non living. They are able to grow inside the body of host organisms only, as they can multiply in the cell. They causes the disease like, common cold, flu, polio, chickenpox and small pox. The other one is HIV virus, which causes AIDS. These viruses are 10 -100 times smaller than the bacteria. They can be observed under the microscope only.

                                       Viruses  

       The single cellular microorganisms, which is classified as animal and is found in lake, ponds and river. They come under the group of protozoa. Identify which one of the following organisms comes in this group?

(a) Entamoeba

(b) Azeto-bacter

(c) Bacilli

(d) Yeast

(e) None of these

Answer: (a)

Explanation

Among the following organisms given in the options only entamoeba is protozoa and rest are either bacteria or algae.

         One of the incurrable diseases is AIDS. It is caused by virus. In this disease virus damages the immunity system of the individual. Which one of the following virus causes AIDS?

(a) Nile virus

(b) Rhinovirus

(c) Retrovirus

(d) Myringitis

(e) None of these

Answer: (c)

Explanation

The AIDs causing virus is Retrovirus.