Hairy T-cell
1665 – Robert Hooke
Used a simple microscope
Observed cells in cork.
Coined the term "cells”.
He thought cells only
existed in plants and Fungi
Anton van Leuwenhoek
• 1673- Used a handmade microscope to observe
pond scum & discovered single-celled
organisms
• He called them “animalcules”
• He also observed blood cells from fish, birds,
frogs, dogs, and humans
• Therefore, it was known that cells are found in
animals as well as plants
Cells are Diverse…
both in size,
shape, and
internal
organization.
How big are cells? Most are
microscopic!!!
• Largest cell on
the human
body =
ovum
• Size=
• 1000 µm in
diameter
(1 mm)
How big are cells?
• Largest cell = yolk of an ostrich egg
Common features of all cells
1. Cell Membrane –
selectively/differentially
permeable (lets some things in
and out)
Common features of all cells
2. Cytoplasm – semi-fluid
material in which cell
organelles float
Common features of all cells
3. Nucleic
acid
containing genetic
code :
DNA
Common features of all cells
4. Ribosomes
– make
proteins
Important events in
the discovery of the
cell and the
development of the
cell theory…..
150-200 Year Gap???
• Between the Hooke/Leuwenhoek discoveries
and the mid 19th century, very little cell
advancements were made.
• This is probably due to the widely accepted,
traditional belief in Spontaneous Generation.
• Examples:
-Mice from dirty clothes/corn husks
-Maggots from rotting meat
Principle 1
•All living things are
made up of Cells
1838 - Matthias Schleiden
A botanist who concluded that all plants are made of cells.
Typical Plant Cell
1839 - Theodor Schwann
A zoologist who concluded that all animals
are made of cells.
Nerve Cells
Principle 2
Development of Cell Theory
, Matthias Schleiden and Theodor Schwann,
are given credit for this part of the cell theory
as well.
The most basic unit of structure in all living
things are cells. They have specific functions
and structures within in living
organisms.(plants and animals)
All cells are basically the same in chemical
composition and metabolic activities.
Principle 3
All Cells come from
existing cells.
1855 - Rudolph Virchow
Much doubt existed around Spontaneous
Generation
A physician who did
research on cancer cells
and concluded
“Omnis cellula e cellula”.
“All cells are from other
pre-existing cells.”
Cells reproduce to make
new cells
The Cell Theory
1. All living things are
composed of one or
more cells.
2. Cells are the basic units of
structure and function in
an organism.
3. Cells come only from
existing cells.