Extra Questions: Class 8 Science Chapter 2 The Invisible Living World

Practice questions beyond the textbook exercise, testing deeper understanding of cells and microorganisms for Class 8 Science Chapter 2: The Invisible Living World. These Class 8 Science Chapter 2 important questions are handy for last-minute exam practice.

Last Updated: September 23, 2026

Extra Questions: Class 8 Science Chapter 2 The Invisible Living World

1. 1 (Assertion-Reason). Assertion: Bacterial cells lack a true nucleus. Reason: Bacteria have a nucleoid instead of a membrane-bound nucleus.
   Solution: Both true, and the reason correctly explains the assertion — a nucleoid is an unbound region of genetic material, unlike the membrane-enclosed nucleus of plant/animal cells.
2. 2 (Applied). A student stores bread in three places: a warm humid kitchen shelf, an airtight dry container, and a refrigerator. Which is likely to grow mould fastest, and why?
   Solution: The warm humid kitchen shelf — mould (a fungus) grows fastest with warmth, moisture and air present; the airtight container lacks moisture/air exchange and the fridge is too cold for rapid growth.
3. 3 (Short Answer). Name one microorganism each that is (i) beneficial in bread-making (ii) beneficial in curd-making (iii) beneficial in soil nitrogen enrichment.
   Solution: (i) Yeast (ii) Lactobacillus (iii) Rhizobium.
4. 4 (Assertion-Reason). Assertion: Salt is used to preserve pickles. Reason: High salt concentration draws water out of microbial cells by osmosis, preventing their growth.
   Solution: Both true, and the reason correctly explains the assertion.
5. 5 (Synthesis). Compare a plant cell and a bacterial cell: name one structure present in both, and one present in only one of them.
   Solution: Both have a cell wall and cytoplasm; plant cells additionally have a true membrane-bound nucleus and chloroplasts, which bacteria lack (bacteria have a nucleoid instead).
6. 6 (Applied). Why does curd form faster in summer than in winter?
   Solution: Lactobacillus bacteria are more active at warmer temperatures, so they ferment lactose into lactic acid faster in summer’s warmth than in winter’s cold.
7. 7 (Short Answer). What structure in a cell controls what enters and leaves it?
   Solution: The cell membrane.
8. 8 (Assertion-Reason). Assertion: Decomposition by microorganisms is essential for the environment. Reason: Microorganisms break down dead matter and recycle nutrients back into the soil.
   Solution: Both true, and the reason correctly explains the assertion.
9. 9 (Applied). A farmer growing lentils (a pulse crop) uses less nitrogen fertiliser than a farmer growing wheat. Explain why, referencing a specific microorganism.
   Solution: Lentils are legumes, and their root nodules host Rhizobium bacteria that fix atmospheric nitrogen into the soil, reducing the need for added fertiliser; wheat lacks this relationship.
10. 10 (Short Answer). Who is considered the first person to observe bacteria, and with what instrument?
    Solution: Antonie van Leeuwenhoek, using single-lens microscopes he built himself.

Frequently Asked Questions

How do beneficial microorganisms like yeast contribute to processes such as bread-making?
Yeast ferments the sugars present in dough, releasing carbon dioxide gas that gets trapped in the dough and causes it to rise, giving bread its characteristic light and airy texture.

Why do certain diseases spread more easily in unhygienic conditions?
Unhygienic conditions provide a favourable environment for harmful microorganisms to multiply and spread more easily through contaminated water, food, or surfaces, increasing the chances of infection.

Written by Satish

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