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

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

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 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

Major Events in Cell Biology and Imaging

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

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

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

• Scanning Electron Microscope (SEM)

• Transmission Electron Microscopes (TEM)

• Scanning Tunneling Microscope

Eyepiece

Stage

Arm

Coarse AdjustmentFine Adjustment

Base

Light Source

Diaphragm

Stage Clips

Objective Lenses

Revolving Nosepiece

Body Tube

Source: http://www.biologycorner.com/microquiz/

Compound Light Microscope

Eyepiece – lens magnifies 10x

Stage – Supports the specimen slide

Arm – Always carry with one hand on the arm and one on the base

Coarse Adjustment – moves stage up or down to bring specimen into focusFine Adjustment – allows for precise focusing

Base – supports the scope

Light Source – provides the light that shines through the

stage

Diaphragm – controls the amount of light reaching the

stage

Stage Clips – hold the specimen slide to the stage

** Objective Lenses – magnify by 4x, 10x, 40x, or

100x

Revolving Nosepiece – holds and rotates objective lenses

Body Tube – supports the eyepiece and objectives

** 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.

Microscope: The Tube that Changed the World