It is chapter 2 of class 9th NCERT science biology

The Fundamental Unit of Life — perfect for revision or quick understanding: - The Fundamental Unit of Life What is the Fundamental Unit of Life? - The cell is the basic structural and functional unit of life. - Discovered by Robert Hooke in 1665 while observing cork under a microscope. - All living organisms are made up of cells — they can be unicellular (one cell) or multicellular (many cells). Types of Cells - Prokaryotic Cells: No true nucleus (e.g., bacteria). - Eukaryotic Cells: Have a well-defined nucleus (e.g., plant and animal cells). Cell Structure and Organelles | Organelle | Function | |----------------------|--------------------------------------------------------------------------| | Cell Membrane | Controls entry/exit of substances; selectively permeable | | Cell Wall | Found in plant cells; provides shape and protection | | Nucleus | Controls cell activities; contains DNA | | Cytoplasm | Jelly-like substance where organelles are suspended | | Mitochondria | Powerhouse of the cell; site of cellular respiration | | Endoplasmic Reticulum (ER) | Transport system; rough ER has ribosomes, smooth ER does not | | Golgi Apparatus | Packaging and transport of proteins and lipids | | Lysosomes | Digestive system of the cell; breaks down waste | | Vacuoles | Storage sacs; large in plant cells, small in animal cells | | Plastids | Found in plant cells; includes chloroplasts for photosynthesis | Key Processes - Diffusion: Movement of molecules from high to low concentration. - Osmosis: Movement of water across a semi-permeable membrane. Tonicity Terms - Hypotonic: Water enters the cell → cell swells. - Isotonic: No net water movement → cell remains same. - Hypertonic: Water leaves the cell → cell shrinks.