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Cell – The Basic Unit of Life
All living organisms are made up of very tiny units called cells. The cell is the smallest structural and functional unit of life. Just like bricks are the basic units of a building, cells are the basic units of our body.
Discovery of Cell
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Robert Hooke (1665): First discovered cells while observing thin slices of cork under a microscope.
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He saw tiny box-like compartments and called them “cells”.
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Later, scientists like Schleiden, Schwann, and Virchow explained that all living organisms are made of cells and new cells arise from pre-existing ones (Cell Theory).
Types of Organisms Based on Cells
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Unicellular Organisms – Made of a single cell (e.g., Amoeba, Bacteria, Paramecium).
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Multicellular Organisms – Made of many cells (e.g., Plants, Humans, Animals).
Shape and Size of Cells
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Cells have different shapes like round, oval, elongated, or irregular.
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Their size can be very small (0.1 micrometer in bacteria) or very large (ostrich egg – the largest single cell).
Structure of a Cell
Every cell has three main parts:
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Cell Membrane (Plasma Membrane) – Outer covering that controls what enters and leaves the cell.
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Cytoplasm – Jelly-like substance inside the cell, where different cell parts (organelles) are present.
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Nucleus – The control center of the cell that contains DNA and controls activities of the cell.
Cell Organelles (small parts inside the cell with special functions)
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Mitochondria – Powerhouse of the cell (energy production).
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Ribosomes – Help in protein synthesis.
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Endoplasmic Reticulum (ER) – Transport system of the cell.
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Golgi Apparatus – Packaging and transport of materials.
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Vacuoles – Storage sacs for food, water, and waste.
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Chloroplasts (only in plant cells) – Help in photosynthesis.
Difference Between Plant Cell and Animal Cell
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Plant Cell has cell wall, chloroplasts, and a large vacuole.
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Animal Cell does not have a cell wall or chloroplasts; vacuoles are small.
The cell is the fundamental unit of life. It performs all essential functions like respiration, growth, and reproduction. Studying cells helps us understand how our body works.
