Class 9 Biology Elaborated Revision – Selected
Chapters (Enhanced)
Chapter 5 – The Fundamental Unit of Life
Cell basics and important facts
• Cell is the smallest structural and functional unit of life.
• Robert Hooke discovered cell in cork (1665); Leeuwenhoek observed living cells.
• Cell theory: all living organisms are composed of cells and cells arise from pre-existing cells.
• Smallest cell: Mycoplasma (~0.1 µm).
• Largest cell: Ostrich egg.
• Longest cell: nerve cell (neuron).
• Human body contains trillions of cells with specialised functions.
Cell membrane & transport
• Plasma membrane is selectively permeable and allows regulated transport.
• Diffusion movement from higher to lower concentration (e.g., O2, CO2 exchange).
• Osmosis movement of water through semipermeable membrane.
• Endosmosis causes swelling; exosmosis causes shrinkage.
• Plasmolysis occurs when plant cell loses water in hypertonic solution.
• Active transport requires energy (ATP).
Cell organelles detailed
• Nucleus contains chromosomes made of DNA and proteins; controls heredity and activities.
• Mitochondria called powerhouse; double membrane with cristae increases surface area.
• Endoplasmic reticulum: RER with ribosomes for proteins; SER for lipids and detoxification.
• Golgi apparatus modifies, packages and transports materials.
• Lysosomes contain hydrolytic enzymes and perform intracellular digestion.
• Ribosomes sites of protein synthesis (free or attached).
• Plastids: chloroplast (photosynthesis), chromoplast (pigments), leucoplast (storage).
• Vacuole large in plant cells; maintains turgor pressure and stores cell sap.
• Centrosome present in animal cells helps spindle formation.
Chapters (Enhanced)
Chapter 5 – The Fundamental Unit of Life
Cell basics and important facts
• Cell is the smallest structural and functional unit of life.
• Robert Hooke discovered cell in cork (1665); Leeuwenhoek observed living cells.
• Cell theory: all living organisms are composed of cells and cells arise from pre-existing cells.
• Smallest cell: Mycoplasma (~0.1 µm).
• Largest cell: Ostrich egg.
• Longest cell: nerve cell (neuron).
• Human body contains trillions of cells with specialised functions.
Cell membrane & transport
• Plasma membrane is selectively permeable and allows regulated transport.
• Diffusion movement from higher to lower concentration (e.g., O2, CO2 exchange).
• Osmosis movement of water through semipermeable membrane.
• Endosmosis causes swelling; exosmosis causes shrinkage.
• Plasmolysis occurs when plant cell loses water in hypertonic solution.
• Active transport requires energy (ATP).
Cell organelles detailed
• Nucleus contains chromosomes made of DNA and proteins; controls heredity and activities.
• Mitochondria called powerhouse; double membrane with cristae increases surface area.
• Endoplasmic reticulum: RER with ribosomes for proteins; SER for lipids and detoxification.
• Golgi apparatus modifies, packages and transports materials.
• Lysosomes contain hydrolytic enzymes and perform intracellular digestion.
• Ribosomes sites of protein synthesis (free or attached).
• Plastids: chloroplast (photosynthesis), chromoplast (pigments), leucoplast (storage).
• Vacuole large in plant cells; maintains turgor pressure and stores cell sap.
• Centrosome present in animal cells helps spindle formation.
