NCERT Class 8 Science Chapter 2
The Invisible Living World: Beyond Our Naked Eye
NCERT Class 8 Science Chapter 2 explores the fascinating world of microorganisms — living things too small to see with the naked eye. This CBSE chapter covers bacteria, viruses, fungi, algae, and protozoa, explaining how they live, reproduce, and affect humans both beneficially and harmfully. Students learn about diseases caused by microbes and how the body and medicine fight them.
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Key Terms
- Microorganism
- A living organism that is too small to be seen with the naked eye and requires a microscope to view; includes bacteria, viruses, fungi, protozoa, and algae.
- Bacteria
- Single-celled microorganisms without a distinct nucleus; can be beneficial (like Lactobacillus in curd) or harmful (like Salmonella causing food poisoning).
- Virus
- Extremely tiny infectious agents that can only replicate inside a living host cell; responsible for diseases like influenza, COVID-19, and polio.
- Fungi
- Microorganisms that include moulds and yeasts; some cause diseases while others are useful in making bread and antibiotics.
- Protozoa
- Single-celled organisms like Amoeba and Plasmodium; Plasmodium causes malaria.
- Antibiotic
- A medicine that kills or stops the growth of bacteria; penicillin was the first antibiotic, discovered from a fungus.
- Vaccine
- A preparation that stimulates the immune system to produce immunity against a specific disease without causing the disease itself.
Frequently Asked Questions
What are microorganisms Class 8?▾
Microorganisms are living things that are too small to be seen with the naked eye. They include bacteria, viruses, fungi, protozoa, and algae. They are studied in NCERT Class 8 Science Chapter 2 and can be found in soil, water, air, and inside living bodies.
What diseases are caused by microorganisms Class 8?▾
Several diseases are caused by microorganisms. Bacteria cause tuberculosis, cholera, and typhoid. Viruses cause influenza, dengue, and polio. The protozoan Plasmodium causes malaria. NCERT Class 8 Chapter 2 lists these diseases along with their causative agents.
What are the useful microorganisms Class 8 Science?▾
Useful microorganisms include Lactobacillus (used in making curd and cheese), yeast (used in baking bread and making alcohol), Rhizobium (fixes nitrogen in soil to improve fertility), and Penicillium (used to produce penicillin antibiotic).
What is the difference between bacteria and virus Class 8?▾
Bacteria are living single-celled organisms that can survive on their own and be killed by antibiotics. Viruses are non-living outside a host, are much smaller than bacteria, and antibiotics do not work against them. Both can cause diseases but are treated differently.
How does a vaccine work Class 8?▾
A vaccine introduces a weakened or dead form of a pathogen (or its proteins) into the body. The immune system responds by producing antibodies. If the real pathogen enters later, the immune system recognises it and fights it quickly, preventing the disease.
What is nitrogen fixation Class 8 Science?▾
Nitrogen fixation is the process by which certain bacteria (like Rhizobium) convert atmospheric nitrogen gas into ammonia or nitrates that plants can absorb from the soil. This process is important for soil fertility and plant growth.
Why can't we see microorganisms with the naked eye?▾
Microorganisms are extremely small — most are measured in micrometres (millionths of a metre). Our eyes cannot resolve objects that small, so we need microscopes to see them. The invention of the microscope allowed scientists to discover this invisible world.
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