NCERT Class 8 Science Science: Chapter 2 — Microorganisms: Friend and Foe
This chapter introduces students to microorganisms, also known as microbes, which are living organisms too small to be seen with the unaided eye. It explains that these microbes are found everywhere, including in soil and water, and can be observed with a magnifying glass or microscope. The chapter classifies microorganisms into four major groups: bacteria, fungi, protozoa, and some algae, with viruses being a distinct category that reproduces only within host cells. Examples of diseases caused by different types of microorganisms are provided, such as cold and flu by viruses, malaria and dysentery by protozoa, and typhoid and tuberculosis by bacteria. The chapter aims to familiarize Class 8 students with the existence and basic classification of these tiny organisms, crucial for their CBSE Science curriculum.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 8 |
| Subject | Science |
| Book | Science |
| Chapter | Chapter 2 — Microorganisms : Friend and Foe |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 2 minutes |
| Word count | 361 |
Learning outcomes
- Define microorganisms and identify where they are found.
- Classify microorganisms into major groups: bacteria, fungi, protozoa, algae, and viruses.
- Recognize that viruses are different from other microorganisms.
- Identify common diseases caused by bacteria, viruses, and protozoa.
- Understand the use of microscopes for observing microorganisms.
Vocabulary
| Word | Meaning |
|---|---|
| Microorganisms | Living organisms that are too small to be seen with the naked eye. |
| Microbes | Another term for microorganisms. |
| Magnifying glass | A lens that produces a magnified image of an object. |
| Microscope | An instrument used to see objects that are too small for the naked eye. |
| Bacteria | A major group of microorganisms, often single-celled. |
| Fungi | A major group of microorganisms, including yeasts and molds. |
| Protozoa | A major group of single-celled microorganisms. |
| Algae | A major group of microorganisms, often photosynthetic. |
| Viruses | Microscopic infectious agents that reproduce only inside living cells. |
| Host organism | An organism that harbors a parasite or pathogen. |
The complete chapter text is read in the official NCERT PDF viewer below (streamed from ncert.nic.in). This page provides NCERT Help study material — summary, vocabulary, practice questions, and FAQs — not a full reproduction of the textbook.
Read chapter online
This PDF is loaded from the official NCERT website (ncert.nic.in). Use the page buttons below to read — download is disabled on NCERT Help.
Read page by page below. PDF is streamed from the official NCERT website — no download button on this page.
Practice questions
- What are microorganisms? Answer: Microorganisms are living organisms that are too small to be seen with the unaided eye.
- Name the four major groups of microorganisms. Answer: The four major groups are bacteria, fungi, protozoa, and some algae.
- Why are viruses different from other microorganisms? Answer: Viruses reproduce only inside the cells of a host organism, unlike other microorganisms.
- Name one disease caused by bacteria and one caused by a virus. Answer: Bacterial disease: Typhoid or Tuberculosis (TB). Viral disease: Cold, influenza (flu), polio, or chicken pox.
Frequently asked questions
What are microorganisms and where are they found?
Microorganisms are tiny living things, invisible to the naked eye, found in soil, water, air, and inside other living beings.
What are the main types of microorganisms?
The main types are bacteria, fungi, protozoa, and some algae. Viruses are also microscopic but reproduce differently.
Can we see all microorganisms?
No, most microorganisms are so small they require a microscope to be seen. Some, like bread mold, can be seen with a magnifying glass.
Which diseases are caused by viruses?
Common ailments like cold, influenza (flu), coughs, polio, and chicken pox are caused by viruses.
What are some diseases caused by bacteria?
Typhoid and tuberculosis (TB) are examples of diseases caused by bacteria.
What is a host organism in relation to viruses?
A host organism is a living cell (like a bacterium, plant, or animal cell) inside which a virus reproduces.
Related resources
Important topics
Topics covered
NCERT Class 8 Science — Science — Chapter 2 — Microorganisms : Friend and Foe. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.