NCERT Solutions for Class 8th Science Chapter 2 The Invisible Living World: Beyond Our Naked Eye
Updated on 2026-09-19
About this chapter
The eye can only see things above a certain size. A curved piece of glass, thick in the middle and thin at the edge — shaped like a lentil seed, which is why it was named a lens — makes small things look bigger. Better lenses became microscopes , and microscopes opened the hidden living world. In 1665 Robert Hooke published Micrographia . His microscope magnified 200 to 300 times . Looking at a thin slice of cork he saw many small empty compartments like a honeycomb, and called each one a cell . Around the 1660s Antonie van Leeuwenhoek made better lenses and was the first to clearly see and describe bacteria and blood cells — the Father of Microbiology . Every living body is built of cells. A typical cell has a cell membrane (porous — lets in what life processes need and lets waste out), c
- Chapter opening
- A water-filled flask behaving like a lens
- How small a thing can the eye actually see?
- What Is a Cell?
- the parts of a cell and what each one does
- Variation in shape and structure of cells
- What Are Microorganisms?
- recording what pond water and soil suspension contain
- How Are We Connected to Microbes?
- Key players in cleaning the environment
Quick revision
| Term | What it means | Where it comes in the chapter | Example or key number |
|---|---|---|---|
| Lens | A curved piece of glass, thick in the middle and thin at the edge, that makes small things look bigger | Page 9 | Named after the lentil seed it was shaped like |
| Cell | The basic unit of life — the ‘brick’ every living body is built from | Pages 10–12, 24 | Named by Robert Hooke in 1665 from cork |
| Cell membrane | The porous outer layer that encloses cytoplasm and nucleus, separates one cell from the next, and controls what enters and leaves | Page 12 | Present in animal, plant, fungal and bacterial cells |
| Cytoplasm | The material between the cell membrane and the nucleus; holds carbohydrates, proteins, fats and mineral salts | Page 12 | Most life processes happen here |
| Nucleus | The round structure in the middle, covered by a thin membrane, that regulates all the cell's activities and its growth | Pages 12–13 | Absent as a well-defined structure in bacteria |
| Cell wall | An extra outer covering around the cell membrane that gives rigidity and strength | Page 13, 24 | Plant, fungal and bacterial cells have one; animal cells do not |
| Plastid / Chloroplast | Tiny rod-shaped structures in plant cells; chloroplasts carry chlorophyll and help in photosynthesis | Page 13 | In non-green parts plastids store substances |
| Vacuole | A large empty-looking space in a plant cell that stores substances, removes waste and keeps the cell's shape | Page 13 | Usually absent or very small in animal cells |
| Levels of organisation | Cell → Tissue → Organ → Organ system → Organism | Page 14 | A group of similar cells makes a tissue |
| Microorganism (microbe) | A living being too small to be seen with the unaided eye | Pages 15–16 | Bacteria, protozoa, fungi, some algae |
| Nucleoid | The region in a bacterial cell that holds its genetic material in place of a well-defined nucleus | Page 24 | Distinguishes bacteria from yeast, protozoa, algae, fungi, plants and animals |
| Virus | Microscopic and acellular; multiplies only after entering a living cell | Page 17 | May infect plants, animals or bacterial cells |
| Decomposition | Microbes breaking complex substances of dead plants and animals into simpler, nutrient-rich substances | Page 19 | Needs optimal temperature and appropriate moisture |
| Biogas | A mixture of gases released by bacteria in an oxygen-free environment, mainly methane with carbon dioxide | Page 20 | Used for cooking, heating, electricity and vehicles |
| Rhizobium | Bacteria living in the root nodules of legumes that trap nitrogen from the air for the plant | Page 22 | Beans, peas and lentils — hence crop rotation |
| Lactobacillus | A bacterium that feeds on lactose, ferments milk into curd and produces lactic acid | Pages 21–22 | Also ferments idli and dosa batter and bhatura dough |
| Microalgae | Microscopic plant-like organisms that make their own food using sunlight | Pages 22–23 | Spirulina, Chlorella, Diatoms; over half of Earth's oxygen |
Exercises
- Chapter opening — Probe and ponder Page 8
- A water-filled flask behaving like a lens — Activity 2.1: Let us observe Page 9
- How small a thing can the eye actually see? — In-text Questions Page 9
- Activity 2.2: Let us study a cell — What Is a Cell? Page 11
- Activity 2.3: Let us investigate — What Is a Cell? Page 12
- In-text Questions — the parts of a cell and what each one does Page 12
- In-text Questions — Variation in shape and structure of cells Page 13
- In-text Questions — What Are the Levels of Organisation in the Body of a Living Organism? Page 14
- In-text Questions — What Are Microorganisms? Page 15
- Activity 2.6: Let us study — recording what pond water and soil suspension contain Page 16
- In-text Questions — How Are We Connected to Microbes? Page 18
- Activity 2.7: Let us do — Key players in cleaning the environment Page 18
- In-text Questions — decomposition and natural manure Page 19
- In-text Questions — and 2.4.2 Page 20
- Ananda Mohan Chakrabarty and the oil-eating bacterium — Be a scientist Page 20
- Activity 2.8: Let us perform — Microorganisms and food Page 20
- Activity 2.9: Let us prepare — Microorganisms and food Page 21
- End-of-chapter question set — Keep the curiosity alive Page 25
- Science · Society · Interdisciplinary Projects — Discover, design, and debate Page 27