1. Introduction to the Cell
Definition: The cell is the basic structural and functional unit of all living things.
Fundamental Unit: It is called "fundamental" because a single cell has the capability to
survive independently, containing all the necessary organelles to sustain life.
Biological Hierarchy: Cells organize into a complex system: Cell → Tissue (group of cells) →
Organ → Organ System → Organism.
2. History and Discovery
Robert Hooke (1665): Discovered the first cells by observing a thin slice of wooden cork
under a microscope. He saw box-like compartments resembling jail cells (called "cells" in
some languages) and coined the term. These were dead plant cells.
Antony van Leeuwenhoek (1674): First to observe living cells using a drop of pond water.
Cell Theory:
o Schleiden and Schwann (1838): Stated that all plants and animals are composed of
cells.
o Rudolf Virchow (1855): Added the third statement: "All living cells arise from pre-
existing cells".
3. Cell Size and Shape
The shape and size of a cell are directly related to its function.
Smallest Cell: Mycoplasma (also known as PPLO), measuring about 0.3 to 5 micrometres.
Largest Cell: Ostrich egg.
Longest Cell: Nerve cell (Neuron), which can be up to 1 metre long to transmit electrical
signals to the brain.
Shape Variations:
o RBCs (Red Blood Cells): Biconcave shape to increase surface area for carrying more
oxygen.
o WBCs (White Blood Cells): Amoeboid (irregular) shape, allowing them to engulf and
kill bacteria.
4. Cell Structure and Organelles
Outer Boundaries
Plasma Membrane: Found in all cells. It is selectively permeable (or semi-permeable),
acting like a "VIP gate" that controls which molecules enter or exit. It follows the Fluid
Mosaic Model, composed of proteins and lipids.
Cell Wall: Present only in plants (cellulose), fungi (chitin), and bacteria. It is a rigid, dead
layer that provides structural support and protection against harsh environments.
The Control Center: Nucleus
Definition: The cell is the basic structural and functional unit of all living things.
Fundamental Unit: It is called "fundamental" because a single cell has the capability to
survive independently, containing all the necessary organelles to sustain life.
Biological Hierarchy: Cells organize into a complex system: Cell → Tissue (group of cells) →
Organ → Organ System → Organism.
2. History and Discovery
Robert Hooke (1665): Discovered the first cells by observing a thin slice of wooden cork
under a microscope. He saw box-like compartments resembling jail cells (called "cells" in
some languages) and coined the term. These were dead plant cells.
Antony van Leeuwenhoek (1674): First to observe living cells using a drop of pond water.
Cell Theory:
o Schleiden and Schwann (1838): Stated that all plants and animals are composed of
cells.
o Rudolf Virchow (1855): Added the third statement: "All living cells arise from pre-
existing cells".
3. Cell Size and Shape
The shape and size of a cell are directly related to its function.
Smallest Cell: Mycoplasma (also known as PPLO), measuring about 0.3 to 5 micrometres.
Largest Cell: Ostrich egg.
Longest Cell: Nerve cell (Neuron), which can be up to 1 metre long to transmit electrical
signals to the brain.
Shape Variations:
o RBCs (Red Blood Cells): Biconcave shape to increase surface area for carrying more
oxygen.
o WBCs (White Blood Cells): Amoeboid (irregular) shape, allowing them to engulf and
kill bacteria.
4. Cell Structure and Organelles
Outer Boundaries
Plasma Membrane: Found in all cells. It is selectively permeable (or semi-permeable),
acting like a "VIP gate" that controls which molecules enter or exit. It follows the Fluid
Mosaic Model, composed of proteins and lipids.
Cell Wall: Present only in plants (cellulose), fungi (chitin), and bacteria. It is a rigid, dead
layer that provides structural support and protection against harsh environments.
The Control Center: Nucleus
