One of the most fascinating Biology Topics is the study of genetics and how traits are passed down through generations.
List the Five Major Groups of Micro-Organisms
Many living organisms are present in soil, water, and air around us. Some of these organisms are so small that we cannot see them with naked eyes. We need a magnifying instrument called microscope to see these extremely small organisms.
These extremely small organisms are known as micro-organisms (micro = extremely small). We can now say that : Those organisms which are too small to be seen without a microscope are called micro-organisms. Thus, micro¬organisms cannot be seen with the naked eye. Micro-organisms can be seen only with the help of a microscope.
Though we cannot see the micro-organisms around us, we become aware of the presence of micro-organisms through their actions like spoiling our food and causing diseases. Thus, some of the micro-organisms are harmful to us. The micro-organisms like certain bacteria and fungi make our food go bad.
The micro-organisms also cause diseases in humans, other animals and plants The diseases like common cold, malaria, skin infections, typhoid, tuberculosis, tetanus, cholera, measles, chickenpox, smallpox and AIDS, etc., are all caused by the action of various types of micro-organisms. Some of the micro-organisms grow on our food and cause food poisoning.
Some of the micro-organisms are also useful to us. For example, the micro-organisms like certain bacteria help in making food products such as curd and cheese. Micro-organisms are also useful in making bread, cakes, pastries, alcohol, acetic acid (vinegar) and medicines called antibiotics.
Some micro-organisms decompose the organic waste of dead plants and animals into simple substances and clean up the environment. They also help in recycling the materials (like carbon and nitrogen) in nature.
Major Groups of Micro-Organisms
Micro-organisms are classified into five major groups. These groups are : Bacteria, Viruses, Protozoa, and some Fungi and Algae. Micro-organisms may be unicellular (single celled) or multicellular (many-celled).
Please note that the singular of bacteria is bacterium; the singular of viruses is virus ; the singular of protozoa is protozoan ; the singular of fungi is fungus ; and the singular of algae is alga. We will now describe the various types of micro-organisms very briefly.
Bacteria are very small, single-celled micro¬organisms which have cell walls but do not have an organised nucleus and other structures (see Figure). Bacteria are found in large numbers everywhere : in air; soil and water ; every surface around us ; on our bodies and even inside our bodies.
Bacteria are larger than viruses but still very small. Unlike viruses, bacteria feed, move and respire, as well as reproduce on their own.
There are mainly three groups of bacteria on the basis of their shape : spherical bacteria, rod¬shaped bacteria and spiral bacteria. The two common examples of bacteria are Lactobacillus bacteria and Rhizobium bacteria.
Some of the bacteria are useful and help in making foods (like curd), nitrogen fixation and decomposition of waste organic matter. On the other hand, some of the bacteria cause diseases. Some of the human diseases caused by bacteria are cholera, typhoid, tuberculosis (TB), diphtheria, whooping cough and food poisoning.
Viruses are the smallest micro-organisms which can develop only inside the cells of the host organisms (which may be animal, plant or bacterium). Viruses are much smaller than bacteria (see Figure). Viruses do not show most of the characteristics of living things.
For example, viruses do not respire, feed, grow, excrete, or move on their own. They just reproduce. Viruses are able to reproduce if they enter a living cell. That is, viruses can reproduce and multiply only inside the cells of other organisms (such as animal cells, plant cells or bacteria cells).
Thus, as long as viruses are outside the living cells, they behave as non-living things. But as soon as the viruses enter the living cells of other organisms, they start behaving as living things by carrying out the process of reproduction. Due to this reason, viruses are said to lie on the border line dividing the living things from non-living things. Viruses are the agents of disease. Viruses cause a variety of diseases in human beings, other animals and plants.
The human diseases such as common cold, influenza (flu), measles, polio, chickenpox, and smallpox are all caused by viruses. The two examples of viruses are ‘common cold virus’ and ‘Human Immunodeficiency Virus’ (HIV). Common cold virus causes common cold disease whereas HIV causes AIDS disease (AIDS stands for Acquired Immune Deficiency Syndrome). Diseases caused by virus (or viral diseases) cannot be treated with antibiotics.
Protozoa are a group of single-celled micro-organisms which are classified as animals. Protozoa are animal like just as algae are plant like. Protozoa are found in ponds, lakes, dirty water drains, rivers, sea-water and damp soil. Some common examples of protozoa are : Amoeba, Paramecium, Entamoeba and Plasmodium. A few protozoa are shown in Figure.
Many protozoa are parasites and cause diseases. Diseases like dysentery and malaria are caused by protozoa. For example, Entamoeba is a protozoan which causes a disease known as amoebic dysentery. And Plasmodium is a protozoan which causes a disease called malaria in humans. Plasmodium is commonly known as ‘Malarial Parasite’ (MP).
Algae is a large group of simple, plant-like organisms. They contain chlorophyll and produce food by photosynthesis just like plants. Algae, however differ from plants because they do not have proper roots, stems and leaves. Some of the examples of algae are : Chlamydomonas, Spirogyra, Blue-green algae ; Diatoms and Seaweeds (see Figure).
Only some of the algae are unicellular. Most of the algae are multicellular. For example, Chlamydomonas and diatoms are single- celled algae whereas blue-green algae and Spirogyra are multicellular algae. The blue-green algae have the ability to fix nitrogen gas of atmosphere.
Fungi are a large group of organisms which do not have chlorophyll and do not photosythesise. Some examples of fungi are : Yeast, Moulds (such as Bread mould, Penicillium and Aspergillus), Mushrooms, Toadstools and Puffballs (see Figure).
All fungi (except yeast) are made up of fine threads called hyphae (pronounced as hi-fee). Some fungi look like plants but they cannot make their own food like the plants do. Fungi need moist and warm conditions to grow.
Most of the fungi are saprophytes which feed on dead things like remains of dead plants and animals. Some of the fungi are parasites. They feed on living things and cause diseases. A mould is a fur-like growth of minute fungi occurring on organic matter in moist and warm conditions. Some of the examples of mould fungi are : Rhizopus (Bread mould), Penicillium and Aspergillus.
he fungi like yeast and moulds are very small in size and can be seen clearly only with a microscope. Thus, yeast and moulds are the fungi which can be considered to be micro-organisms. The fungi such as mushrooms, toadstools and puffballs are bigger in size. Some of the human diseases caused by fungi are ringworm and athlete’s foot.
Where Do Micro-Organisms Live
Micro-organisms are found practically everywhere in all types of habitats. Micro-organisms are found in air, soil and water bodies (like ponds, lakes, wells, rivers and sea). Micro-organisms can live and survive in almost all kinds of environment like hot springs, ice-cold waters, saline water (salty water), desert soil or marshy land.
They also occur in dead and decomposed organic matter (plant and animal matter). Micro-organisms are present inside the human body and that of other animals. The micro-organisms also live as parasites on other living things, including us.
We can show the presence of micro-organisms in soil and water by performing the following activities:
(i) Collect some moist soil from the field in a beaker and add water to it. After the soil particles have settled down, observe a drop of water from the beaker under a microscope. We will see tiny organisms moving around. This observation shows that soil contains micro-organisms.
(ii) Take a few drops of water from a pond. Spread this water on a clean glass slide and observe through a microscope. We will see some tiny organisms moving around. This observation shows that pond water contains micro-organisms.