Cell: The Unit of Life
1. Introduction to the Cell
Definition: The cell is the fundamental, structural, and functional unit
of life.
Defining Feature: The presence of a cell is a defining feature of living
organisms and is mandatory in all living things.
Function: All major functions of the body are performed inside cells.
Diversity: The human body contains more than 200 different types of
cells.
Cell Biology: The study of cell structure, function, and division.
2. Discovery of the Cell
Robert Hooke (1665): Observed cork cells using simple lenses; he
named them "Cellula" (empty compartments). These were dead cells
without cytoplasm. He authored the book Micrographia.
Dead cork cell
Honeycomb like structure
, Anton van Leeuwenhoek (1674): First to observe living, motile cells
like bacteria, sperm, and protozoa, which he called "animalcules".
Robert Brown (1831): Discovered the nucleus.
3. Types of Organisms
Unicellular: Single-celled organisms capable of independent existence
and performing all life functions (e.g., Bacteria, Amoeba, Paramecium).
Multicellular: Organisms composed of many cells (e.g., Plants,
Animals, Fungi—except yeast).
Note: Anything less than a cell cannot survive independently;
therefore, viruses are not considered living.
4. Cell Theory
Schleiden (1838): German Botanist who stated all plants are
composed of different types of cells which form tissues.
Schwann (1839): German Zoologist who observed animal cells have a
thin outer layer (cell membrane) and plant cells have a cell wall.
Core Principle: All organisms are formed of cells and products of
cells.
Rudolf Virchow (1855): Added the concept "Omnis cellula-e-cellula",
meaning new cells arise from pre-existing cells.
5. Prokaryotic vs. Eukaryotic Cells
Feature Prokaryotic Cell Eukaryotic Cell
Not well-defined; no nuclear
Nucleus Well-defined with a nuclear envelope.
membrane.
Organelles Membrane-bound organelles absent. Membrane-bound organelles present.
Ribosomes 70s. 80s (cytoplasm) and 70s (organelles).
Usually bigger; divides slowly (e.g.,
Usually smaller; divides faster (e.g., E. Human cell in 24 hrs).
Size/Division
coli in 20 mins).
1. Introduction to the Cell
Definition: The cell is the fundamental, structural, and functional unit
of life.
Defining Feature: The presence of a cell is a defining feature of living
organisms and is mandatory in all living things.
Function: All major functions of the body are performed inside cells.
Diversity: The human body contains more than 200 different types of
cells.
Cell Biology: The study of cell structure, function, and division.
2. Discovery of the Cell
Robert Hooke (1665): Observed cork cells using simple lenses; he
named them "Cellula" (empty compartments). These were dead cells
without cytoplasm. He authored the book Micrographia.
Dead cork cell
Honeycomb like structure
, Anton van Leeuwenhoek (1674): First to observe living, motile cells
like bacteria, sperm, and protozoa, which he called "animalcules".
Robert Brown (1831): Discovered the nucleus.
3. Types of Organisms
Unicellular: Single-celled organisms capable of independent existence
and performing all life functions (e.g., Bacteria, Amoeba, Paramecium).
Multicellular: Organisms composed of many cells (e.g., Plants,
Animals, Fungi—except yeast).
Note: Anything less than a cell cannot survive independently;
therefore, viruses are not considered living.
4. Cell Theory
Schleiden (1838): German Botanist who stated all plants are
composed of different types of cells which form tissues.
Schwann (1839): German Zoologist who observed animal cells have a
thin outer layer (cell membrane) and plant cells have a cell wall.
Core Principle: All organisms are formed of cells and products of
cells.
Rudolf Virchow (1855): Added the concept "Omnis cellula-e-cellula",
meaning new cells arise from pre-existing cells.
5. Prokaryotic vs. Eukaryotic Cells
Feature Prokaryotic Cell Eukaryotic Cell
Not well-defined; no nuclear
Nucleus Well-defined with a nuclear envelope.
membrane.
Organelles Membrane-bound organelles absent. Membrane-bound organelles present.
Ribosomes 70s. 80s (cytoplasm) and 70s (organelles).
Usually bigger; divides slowly (e.g.,
Usually smaller; divides faster (e.g., E. Human cell in 24 hrs).
Size/Division
coli in 20 mins).
