Microorganisms: Friends and Foe
Q1: Name the microorganisms which can fix atmospheric nitrogen in the soil.
Answer:
Bacteria such as Rhizobium, Azotobacter, and certain blue-green algae present in the soil fix atmospheric nitrogen in the soil.
Q2: Can microorganisms be seen with the naked eye? If not, how can they be seen?
Answer:
Microorganisms are so tiny in size that they cannot be seen with the naked 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 also called microbes.
Q3: What are antibiotics?
Answer:
Antibiotics are medicines that fight infections caused by bacteria in humans and animals by either killing the bacteria or making it difficult for the bacteria to grow and multiply.
NCERT Notes Class 8 Science Chapter 2: Microorganisms: Friend and Foe
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.