Harmful Microorganisms

Microorganisms are harmful in many ways. Let’s study their harmful activities:

• Disease-causing Microorganisms in Humans: Disease-causing microorganisms are called pathogens. Pathogens enter our bodies through the air we breathe, the water we drink, or the food we eat. 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, the common cold, chicken pox, and tuberculosis. There are some insects and animals which act as carriers of disease-causing microbes. Housefly is one such carrier. Another example of a carrier is the female Anopheles mosquito, which carries the parasite of malaria (Plasmodium).
• Disease-causing Microorganisms in Animals: Several microorganisms not only cause diseases in humans but also in other animals. For example, anthrax is a dangerous human and cattle disease caused by a bacterium. Foot and mouth disease in cattle is caused by a virus.
• Disease-causing Microorganisms in Plants: Several microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple, and others. The diseases reduce the yield of crops. Some common plant diseases are Citrus canker, Rust of wheat, and Yellow vein Virus Insect mosaic of Bhindi.
• Food Poisoning: Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death. So, it is very important that we preserve food to prevent it from being spoilt.

NCERT Notes for Class 8 Science Chapter-2: Microorganisms: Friend and Foe: Organisms that can be seen only through a microscope are known as Microorganisms or Microbes. These microorganisms 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. That is why these are called microorganisms or microbes. They exist in vast numbers and play vital roles in our lives.

Friends and Foe explain that Microorganisms can be both our friends, providing numerous benefits, or our foes, causing harm and disease. Microorganisms are classified into four major groups. These groups are bacteria, fungi, protozoa, and some algae. Viruses are also microscopic but are different from other microorganisms. Common ailments like colds, influenza (flu) and most coughs are caused by viruses. Serious diseases like polio and chicken pox are also caused by viruses. Diseases like dysentery and malaria are caused by protozoa(protozoans) whereas typhoid and tuberculosis (TB) are bacterial diseases.