1. Discovery of the Cell Robert Hooke (1665) English scientist
looked at a thin slice of cork (oak cork) through a compound microscope
observed tiny, hollow, room-like structures
called these structures “cells” because they reminded him of the rooms that monks lived in
only saw the outer walls (cell walls) because the cork cells were not alive

2. Discovery of the Cell Anton van Leeuwenhoek (mid-1600s)
Dutch fabric merchant and amateur scientist
looked at blood, rainwater, scrapings from teeth through a simple microscope (1 lens)
observed living cells; called some “animalcules”
some of the small “animalcules” are now called bacteria

3. Major Events in Cell Biology and Imaging

4. Development of Microscopes
van Leeuwenhoek’s microscope was considered a simple light microscope because it used one lens and natural light
Hooke’s microscope was compound because it used two lenses

5. Development of Microscopes
In the 200 years after Hooke, compound light microscopes have improved to magnify objects 1500 times using two lenses and a beam of light
Electron microscopes use a beam of electrons to magnify objects 500,000 times!
This power allows us to see the structures on the surface and within the cell

6. Electron Microscopes Scanning Electron Microscope (SEM)
Scans the surface of cells to show their three-dimensional shape
Transmission Electron Microscopes (TEM)
Sends electrons through a specimen to show the parts inside the cell
Scanning Tunneling Microscope
Uses electrons to investigate atoms on the surface of a molecule

7. Scanning Electron Microscope (SEM)
Transmission Electron Microscopes (TEM)
Scanning Tunneling Microscope

8. Compound Light Microscope Eyepiece
Body Tube
Revolving Nosepiece
Arm
Objective Lenses
Stage
Stage Clips
Coarse Adjustment
Diaphragm
Fine Adjustment
Light Source
Base
Source:

9. Eyepiece – lens magnifies 10x
Arm – Always carry with one hand on the arm and one on the base
Stage – Supports the specimen slide
Coarse Adjustment – moves stage up or down to bring specimen into focus
Fine Adjustment – allows for precise focusing
Base – supports the scope

10. Body Tube – supports the eyepiece and objectives
Revolving Nosepiece – holds and rotates objective lenses
** Objective Lenses – magnify by 4x, 10x, 40x, or 100x
Stage Clips – hold the specimen slide to the stage
Diaphragm – controls the amount of light reaching the stage
Light Source – provides the light that shines through the stage
** Since the eyepiece had a magnification of 10x, the total magnification when using the 4x objective lens would be 40x. When using the 10x objective lens, the total would be 100x. When using the 40x lens, the total would be 400x.

11. Cell Theory
Two scientists, Matthias Schleiden and Theodore Schwann (1830s) expanded upon Hooke’s observation of “cells”
Their observations in plants and animal cells have been summarized as the Cell Theory
The Wacky History of Cell Theory

12. The Cell Theory 1. All organisms are composed of one or more cells
2. The cell is the basic unit of organization of organisms
Unicellular organisms – made of one cell that must perform all life’s activities
Multicellular organisms – made of more than one cell. Each cell performs most of the major functions of life
3. All cells come from preexisting cells
Before the cell theory, people did not know where these cells came from. People learned that a cell divides to form two identical cells
The ability of a cell to divide is the basis for
all reproduction (sexual and asexual)
Growth and repair of all multicellular organisms