The document outlines the historical development of cell biology, starting from ancient observations and the classification of organisms by Aristotle to the discovery of cells by Robert Hooke in 1665. It highlights key milestones such as the introduction of the microscope and the eventual formulation of cell theory in the 19th century, which states that all living organisms are composed of cells and that cells arise from preexisting cells. Additionally, it discusses the modern advancements in cell theory, emphasizing the roles of DNA and cellular activities.

1. An Introduction
Lecture # 3
29th Feb 2016
Cell Biology

3. Ancient Times
 Ancient peoples are always on the look-
out for ways that organisms can be used
by them.
 They pass on their understanding orally.
 Some civilizations support “great
thinkers” – and philosophers, but they
rarely base their thoughts on observation
or experiments

4. 334 B.C - Aristotle
 Greek philosopher, Aristotle, begins
to observe nature.
 He classifies all known organisms as
either a Plant or and Animal.
 He writes that living things can arise
spontaneously from non-living matter.

5. 1268 – 1st Eyeglasses
 Roger Bacon, an English man
makes reference to a pair of eye
glasses.
 This means that glass is being
developed and used in a way that
makes it easier to see small
things.

6. 1500’s
 Most European’s think that
knowledge is unchangeable
and should not be
questioned.
 To find answers about
nature, they look to the
original teachings of
Aristotle.

7. 1590 – 1st Microscope
 Zacharias Janssen, a Dutch eyeglass
maker, makes the 1st microscope by
placing two lenses on top of one
another to make extra-large images.

8. 1600’s
 People start to question the origins of
life.
 Many begin to suggest that life can
only come from other forms of life
rather than through spontaneous
generation (as was suggested by
Aristotle). This only took about 2000
years!
 William Harvey says that maggots do
not come from the meat itself but
from tiny eggs too small to be seen.
William
Harvey
English
Physician
1578-1657

9. 1665- 1st cell seen
 Discovery of Cells
 English Scientist, Robert Hooke,
discovered cells while looking at a thin
slice of cork.
 He described the cells as tiny boxes or a
honeycomb
 He thought that cells only existed in
plants and fungi

10. 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

11. 1667 – Species Defined
 John Ray (1627-1705) defines a
“species” as a set of individuals that
can reproduce their own kind.
 The beginning of the end of
spontaneous generation!

12. 1668 – 1st Experiments about origins
of maggots
 Francesco Redi (1626-1697) conducts
experiments to prove that maggots do not appear
in meat if flies cannot land on it!

13. 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

14. 1830 – Cells are studied
 Biology is becoming an
important science and the
body of knowledge is
growing, especially since the
improvement of microscopes.
 Scientists begin to study the
cell extensively!

15. Development of Cell Theory
 1838- German Botanist, Matthias Schleiden,
concluded that all plant parts are made of cells
 1839- German physiologist, Theodor Schwann, stated
that all animal tissues are composed of cells

16.  1858- Rudolf Virchow, German physician, after
extensive study of cellular pathology, concluded that
cells must arise from preexisting cells.

17. The Cell Theory Complete
The 3 Basic Components of the Cell Theory were now
complete:
 1. All organisms are composed of one or more cells.
(Schleiden & Schwann)(1838-39)
 2. The cell is the basic unit of life in all living things.
(Schleiden & Schwann)(1838-39)
 3. All cells are produced by the division of preexisting
cells. (Virchow)(1858)

18. Modern Cell Theory
Modern Cell Theory contains 4
statements, in addition to the original
Cell Theory:
 The cell contains hereditary information(DNA) which
is passed on from cell to cell during cell division.
 All cells are basically the same in chemical
composition and metabolic activities.
 All basic chemical & physiological functions are
carried out inside the cells.(movement, digestion,etc)
 Cell activity depends on the activities of sub-cellular
structures within the cell(organelles, nucleus, plasma
membrane)

19. Education is the ability to
listen to almost
anything without losing
your temper or your self
confidence
Robert Frost