NCERT Solutions for Class 9th Science Chapter 2 Cell: The Building Block of Life
Updated on 2026-09-08
About this chapter
The unaided eye resolves about 0.1 mm at its near point of 25 cm. Most plant and animal cells are 10–100 µm across, so a light microscope (typically 10X eyepiece × 10X objective = 100X ) is needed; an electron microscope reaches the nanometre scale. The cell membrane is 7–10 nm thick, built of a lipid bilayer with proteins embedded in it — the fluid-mosaic model . It is selectively permeable : water crosses freely, dissolved salt and sugar do not. Diffusion is the net movement of particles down a concentration gradient, with or without a membrane. Osmosis is the diffusion of water across a selectively permeable membrane — the reason a potato piece gains weight in plain water and loses it in 20 per cent salt solution. Plant, fungal and bacterial cells have a rigid, freely permeable cell wal
- The four questions the chapter sets out to answer
- How to Study Cells?
- Cell membrane
- Cell wall
- The Cell Interior
- Threads of Curiosity
- Lysosomes
- Plastids
- Plastids and Vacuoles
- Why do eukaryotic cells need these organelles?
Exercises
- The four questions the chapter sets out to answer — Think It Over Page 8
- In-text Questions — How to Study Cells? Page 9
- In-text Question — How to Study Cells? Page 10
- Activity 2.1: Let us estimate the size of a cell — How to Study Cells? Page 10
- In-text Question — Cell membrane Page 11
- Activity 2.2: Let us experiment — Cell membrane Page 11
- What if… — Cell membrane Page 12
- In-text Question — Cell wall Page 13
- Activity 2.3: Let us investigate — Cell wall Page 13
- Pause and Ponder — Cell wall Page 14
- Activity 2.4: Let us study — The Cell Interior Page 14
- In-text Question — The Cell Interior Page 15
- Threads of Curiosity — In-text Question Page 16
- Lysosomes — In-text Question Page 17
- Plastids — In-text Question Page 18
- Plastids and Vacuoles — In-text Questions Page 19
- Pause and Ponder — Why do eukaryotic cells need these organelles? Page 19
- In-text Question — How do Normal Cells Grow and Divide? Page 20
- Activity 2.5: Let us enhance our skills — How do Normal Cells Grow and Divide? Page 20
- Pause and Ponder — Cell division Page 22
- Threads of Curiosity — In-text Question Page 23
- Ready to Go Beyond — Do cells grow and reproduce forever? Page 23
- End-of-chapter questions — Revise, Reflect, Refine Page 24
- Project work — The Journey Beyond Page 27
- Questions to carry forward — The Quest Continues … Page 27