- Cell theory states that the cell is the fundamental unit of life, cells are structurally and functionally similar, and organisms arise from pre-existing cells. - Key developments included Hooke and Leeuwenhoek observing cells under microscopes in the 1600s, Brown discovering the nucleus in 1831, Schleiden and Schwann establishing that plants and animals are made of cells in 1838-1839, and Virchow proposing that all cells come from pre-existing cells in 1858. - There are two main types of cells - prokaryotic cells which lack nuclei and organelles and eukaryotic cells which have distinct nuclei surrounded by membranes and organelles like mitochondria and Golgi bodies.

1. Modern Cell Theory
Cell Theory
•Cell is regarded as a fundamental structural and func�onal unit of life.
Cell Introduc�on
Robert Hooke observed dead
cells in a thin cork slice through
a self-made microscope &
published this informa�on in his
book ‘Micrographia’.
He gave the name 'Cell'.
Antonie van Leeuwenhoek
designed an improved microscope
and observed first free-living
cells (Bacteria)
PART - 1
1665
Robert Brown, a Sco�sh Botanist
discovered nucleus.
A French Zoologist Dujardin
discovered the semifluid living
material inside a cell and named
it Sarcode.
Purkinje renamed it as
‘Protoplasm – The First Substance’
M.J. Schleiden
A German botanist (1838)
All plants are made up of cells
Rudolf Virchow presented the idea ‘Omnis Cellula e Cellula’ in (1858) and gave the idea
that all living cells arise from pre-exis�ng cells.
1674
1831
1834
1840
T. Schwann
A German zoologist (1839)
All animals are made up of cells
Commonly presented
CELL THEORY
POSTULATES
•All living organisms are composed of cells.
•All cells are basically alike in structure and func�ons.
•The func�on of an organism as a whole is the result of the ac�vi�es
and interac�ons of cons�tuents of the cell.

2. Cell Introduc�on PART - 2
Prokaryo�c cell
Pro - Primi�ve; Karyon - Nucleus
Eukaryo�c cell
Pilus
Ribosome
Capsule
Cell wall
Flagellum
Nucleoid (DNA)
Cell membrane
Cell membrane
Nucleus
Nucleolus
Endoplasmic
re�culum
Golgi complex
Vacuole
Mitochondrion
Cytoplasm
Lysosome
TYPES OF CELLS
Eu - True; Karyon - Nucleus
The nuclear membrane is absent.
Content of nucleus present in the
cytoplasm in a region known as
nucleoid.
Nucleus dis�nct with the nuclear
membrane.
Size: 1µm to 10 µm Size: 5 µm to 100 µm
Membrane-bound cell organelles
are absent.
Membrane-bound cell organelles
like Golgi bodies, mitochondria
etc. are present.
Ribosome - 70 S Ribosome - 80 S
A single circular chromosome is
present
Many chromosomes are present
which are linear.
Shape & Size Varies from cell to cell
Respiratory enzymes are formed
in mitochondria.
CELL FACTS
Longest cell in human body - Nerve cell (1m long)
Smallest cell in human body - Red blood cells
Largest cell in human body - Female ovum
In mul�cellular organisms
division of labour is seen.
Respiratory enzymes are present in
mesosome.
- In unicellular organisms a single
cell perform all the func�ons.
(Amoeba)