The microscope enabled the discovery of cells. In 1665, Hooke observed box-shaped structures in cork which he called "cells". Van Leeuwenhoek later saw living organisms in pond water and milk using an improved microscope. In the 1830s, scientists established that plants and animals are composed of cells, and that cells only arise from pre-existing cells (Cell Theory). Modern compound and electron microscopes allow detailed study of prokaryotic and eukaryotic cell structures and organelles.

1. Cells

2.  For centuries, scientists had no idea
that the human body consists of trillions
of cells.
 What piece of technology made the
discovery of cells possible?
 Answer: The microscope!

3. History
 In 1665 Robert Hooke
made a simple microscope
and looked at a piece of
cork.
 What did he see?
 Small, box-shaped
structures that he called
“cells” because they
reminded him of cells in
which monks lived.

4. History
 During the late 1600’s,
Dutch scientists Anton van
Leeuwenhoek designed his
own microscope and looked
at pond water and milk.
 What did he see?
 Living organisms that they
never knew were there!

5. History
 1838 German scientist
Matthias Schleiden
studied plants and
concluded that all plants
are made of cells.

6. History
 1839 another
German scientist,
Theodor Schwann
reported that animal
tissues are also
made of cells.

7. History
 1855 Virchow proposed
that all cells are
produced from the
division of existing cells.

8. Cell Theory
 The observations of all of these scientists
were summarized as what we know today
as “Cell Theory”
1. All living organisms are composed of one
or more cells.
2. Cells are the basic unit of structure of all
living organisms.
3. Cells come from pre-existing cells.

9. Microscope Technology
Microscopes have enabled scientists to
study cells in detail!

10. Compound Light Microscopes
 These are the
microscopes we use
in class.
 Consists of a series
of glass lenses and
uses light to
produce an image.

11. Compound Light Microscope

12. Electron Microscopes
Transmission Electron Microscope (TEM);
 Electrons are used to view an object at
500,000x
 Give a cross section view of the object
Scanning Electron Microscope (SEM);
 Uses electrons to produce a 3-D image of an
object.

13. Electron Microscopes

14. Prokaryotic Eukaryotic
Cells
•Cells without membrane-
bound organelles
•No true Nucleus
•Smaller than Eukaryotic
•Ex. Bacteria
•Cells with membrane-
bound organelles
•Contain a true nucleus
•Larger than prokaryotic
•Ex. Animals, Plants,
Fungi, Protist

15. Eukaryotic vs. Prokaryotic