Organic Affecting Human Health: Microorganism: Very minute living organisms not seen without the aid of microscope are called microorganisms. There are numerous microorganism but ones which concerns us are germs or disease causing microorganism (called pathogens). They are found almost everywhere in nature (in air, water and soil), on the surface of the objects and living organisms, within the living organisms.

Pathogenic microorganisms are viruses many bacteria, certain fungi and some protozoan.


Viruses cause disease in living cells and are the smallest disease causing particles known. They are only visible under electron microscope. Chickenpox, measles, poliomyelitis, the common cold, mumps, influenza and aids are a few diseases caused by viruses.


Fig. 20.8 structure of virus


Bacteria are larger than viruses and are visible under the ordinary light microscope. All of the bacteria are not pathogens.

Some of the diseases caused by bacteria include boils, food poisoning, whooping coughs, cholera, diphtheria, typhoid, bacillary dysentery, TB etc.


Fig 20.9 structure of bacterium/p>

Protozoa are single-celled organisms which vary in size and shape. Very few of them cause disease in humans. Some common diseases caused by protozoa are malaria, amoebic dysentery, some types of ulcers in large intestine, etc.


Very few fungi are responsible for causing human diseases. Most of the fungi are multi-cellular but some are unicellular. Their mode of nutrition is saprotrophic but very few of them are human parasites. Common fungal human diseases are Ring worm, Athlete’s foot, histoplasmosis, candidia (thrash) etc.

Ring worm

Ring worm is a skin disease caused by fungus. The disease is spread by spores of the fungus which are passed from one individual to another by personal contact or by contact with clothing since the fungus can grow on clothing or other personal objects. Hyphae of the fungus penetrate the outer layers of the skin and grow in the normal way. The red patch as it spreads causes intense itching. As the fungus grows, the center loses its colour to normal leaving a circular red patch which is darker at the edge. The name ‘ring worm’ is given because of this appearance.


Fig 20. 10 fungus which causes ring

Athlete’s foot

Athlete’s foot is also a fungal disease. It is sort of ringworm of the foot. Fungus attacks soft skin between the toes and in bad cases spreads over the whole foot. The skin peels off leaving very sore patches.

Infected floors and mats spread the problem.


Fig. 20. 11 athlete’s foot

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