Summary
The cell is the basic structural and functional unit of all living organisms. All living organisms are composed of cells, and all cells arise from pre-existing cells.
Chapter 2 of NCERT Class 9 Science (Exploration edition) covers the cell as the fundamental unit of life. It explains how cells are studied using light and electron microscopes, describes the structure and function of the cell membrane (selectively permeable, fluid-mosaic model), cell wall (found in plants, fungi, and bacteria), and key organelles including the nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria, plastids, and vacuoles. The chapter also covers prokaryotic vs eukaryotic cells, cell division (mitosis and meiosis), and the classical Cell Theory formulated by Schleiden, Schwann, and Virchow.
Key points & formulas
- 01The cell is the basic structural and functional unit of all living organisms; unicellular organisms like bacteria consist of a single cell, while multicellular organisms like humans have millions of cells working together.
- 02Prokaryotic cells (e.g., bacteria) lack a well-defined nucleus and membrane-bound organelles; eukaryotic cells (plants and animals) have a true nucleus and membrane-bound organelles.
- 03The cell membrane is selectively permeable and follows the fluid-mosaic model — a lipid bilayer with embedded proteins that act as gatekeepers for substance transport.
- 04Plant cells have a rigid cell wall made primarily of cellulose outside the cell membrane, which provides structural support; animal cells lack a cell wall and can change shape more freely.
- 05Mitochondria are the powerhouses of the cell, producing ATP through cellular respiration; chloroplasts in plant cells carry out photosynthesis using chlorophyll to absorb sunlight.
- 06Mitosis produces two genetically identical daughter cells for growth and repair, while meiosis produces four daughter cells with half the chromosome number, used in sexual reproduction.
Frequently asked questions
01What are the three statements of the classical Cell Theory?
The classical Cell Theory, formulated by Schleiden (1838), Schwann (1839), and Virchow (1855), states: (1) All living organisms are made up of one or more cells; (2) The cell is the basic unit of structure and function in living beings; (3) All cells arise from pre-existing cells.
02What is the difference between osmosis and diffusion?
Diffusion is the net movement of particles from a region of higher concentration to lower concentration and can occur without a membrane. Osmosis is a specific type of diffusion — the movement of water through a selectively permeable membrane from a dilute solution (more water, less solute) to a concentrated solution (less water, more solute) until concentrations equalise.
03Why do plant cells not shrink when placed in concentrated sugar solution, unlike animal cells?
Plant cells have a rigid cell wall outside the cell membrane. When placed in concentrated sugar solution, plant cells lose water by osmosis and the inner cell membrane pulls away from the wall, but the rigid cell wall maintains the cell's overall shape and size. Animal cells like cheek cells lack a cell wall, so they shrink considerably when they lose water.
04Is the NCERT Class 9 Science Chapter 2 PDF free to download?
Yes, the NCERT Class 9 Science Chapter 2 PDF is completely free to download on cbseprepmaster.com.
More chapters in Exploration
This is the complete Exploration Chapter 2 as published by NCERT — every diagram, solved example, and exercise included, free. Browse all NCERT Class 9 textbooks.
Read offline with notes, solutions & mock tests
CBSE Prepmaster — free on iOS & Android