Disease Causing Microorganisms

We have heard time and again that we need to keep ‘germs’ away! ‘Germs’ are actually another word for microorganisms or microbes. These can affect both plants and animals and cause diseases in them. This is why we need to keep ourselves and surroundings clean. Let’s read more about the disease causing microorganisms.

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What are these ‘germs’? 

They are small living organisms that are present everywhere- on us, inside us and in our surroundings and cannot be seen with the naked eye. Special devices called the microscope help us see and study them. However, it is important to note that not all microorganisms are bad. We can broadly classify these into ‘good’ and ‘bad’ microorganisms. The ‘good’ microorganisms help in the routine body functions such as digestion, immunity and coexist inside our body all the time. The ‘bad’ microorganisms are the ones that we need to stay clear of because they make us fall ill by causing diseases.

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In biology, disease-causing micro-organisms can be classified into four main groups:

  • Bacteria
  • Virus
  • Fungus
  • Protozoa

These ‘bad’ micro-organisms or disease causing microorganisms are always looking for a chance to enter our body and cause a disease. Most diseases in the world are caused by these micro-organisms, for example, the common cold and flu, malaria, diarrhoea, pneumonia, urinary tract infections, chicken pox, Hepatitis, polio etc.

You can download Microorganisms Cheat Sheet PDF by clicking on the Download button below

microorganisms cheat sheet

microorgamisms cheat sheet

How do these disease causing microorganisms function in the human body?

Disease causing microorganisms outnumber our body cells in a large way. They are present on the skin and various orifices of our body through which they can enter into the system such as:

  • Respiratory tract
  • Genital Tract
  • Urinary tract

Once these microbes enter the system, depending on their own constitution, they look for their target site and attach themselves there. Once they firmly attach themselves, they release toxins and enzymes to stay grounded and at the same time start multiplying and increase in number. The microbes derive nutrition from the host’s body. The toxins and enzymes released by these microbes make the cells of the host weak or ‘ill’ or affected. These toxins can even be spilt into the bloodstream and reach other parts of the body which can also be affected. This way the microbes are able to make the body they are in sick! The manifestation of these toxins and enzymes released on the tissues are varied such as inflammations, swellings, bleeding, wounds, pustules, fever, sneezing, itching and general weakness in the body.

What does the host’s body do?

If you think the microbes have their way once they are in, then you are wrong! The human body is designed to keep all disease-causing elements out of it. The human body always has its defences up even before the microbes enter. For this reason, keeping ourselves clean, healthy and alert is essential. By doing so we do not allow close contact with these microorganisms and so minimise their chances of entering the system.

But, there are many times when the microbes enter the body and find their favourite spot. In these cases, the body’s ‘immune system’ consisting of defence cells are activated. From the time of the microbes entry into the body till the time the body fights it and its products, the immune system is on high alert. The defence cells of the body constitute mainly of two types of cells: T-Lymphocytes and B- Lymphocytes. They both have a different sub-types and modes of action. Together, they are responsible for eradicating the pathogen as a whole either by engulfing it (phagocytosis) or releasing their remedial toxins (antibodies) against the toxins and enzymes of the microbes. Imagine it to be a battle-field between the disease causing pathogens and the body’s armed forces -the T and B- Lymphocytes.

The end result depends upon whose defences are higher. A healthy body which is well nourished is better equipped to fight a microbial invasion compared to a not-so-healthy body. Therefore, it is essential to stay fit. When the body isn’t able to fight back on its own, help is given from outside in the form of antibiotics(for bacteria), antivirals(viruses), antifungals(fungus) and anti-helminthic(protozoa). These can be either in the tablet or capsule form or vaccinations.


Microbes can be transmitted through different routes: few are airborne, few are waterborne, some travel on top of other animals, some are transmitted through human touch, some through touching contaminated surfaces or objects and some though ingesting contaminated water and food. Keeping clear of obvious contaminated or infected areas is important.

In case of plants, there is a host defence mechanism that helps fight these microorganisms as in the case of animals. But, the microorganisms that affect plants and animals are very different. Different species of bacteria, virus and fungi affect plants.

Disease causing pathogens are therefore present everywhere. Whether they are able to enter our body and cause a disease is in our hands to a large extent. Advances in medicine have been made to make our body’s immune system stronger with preventive medicines and vaccinations. There have been biotechnological advances to protect plants as well from infestations and plant diseases.

Let’s do our bit daily to stay fit and healthy, as it is absolutely essential.

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