Cells and the Origin of Cell Theory

History of the Cell Theory

• Before microscopes, belief in supernatural causes of diseases

• Could not see microorganisms

• What branch of biology?

• Cells = basic units of living organisms

Microscopes

• Originally a hand lens to view quality of cloth

• Anton van Leeuwenhoek (mid-1600s) first to examine water under microscope

• Credited with development of light microscope

Anton von Leeuwenhoek’s Microscope

Improvements• Compound light

microscope- series of lens to magnify objects (1500x)

• Robert Hooke used one to observe cork magnified 30x

• Observed small geometric shapes

• Dubbed these cells (resembled monk rooms)

Hooke’s Microscope

Cell Theory

• 1830’s German scientist Matthias Schleiden realized that plants made up of cells

• Theodore Schwann made same determination of animals

• = Cell Theory

• Many resources (including your book) give only credit to Scleiden and Schwann

• Original third tenet was spontaneous generation

• Rudolph Virchow - "Omnis cellula e cellula”

Cell Theory

• All organisms are composed of one or more cells

• The cell is the basic unit of organization of organisms

• All cells come from preexisting cells

Recent Developments• 1940’s were able to use

beam of electrons instead of light

• 500 000x• Electron microscope• Scanning Electron

Microscope • Transmission Electron

Microscope

Scanning Electron Microscope

• SEM

• Electrons are reflected off the surface of the specimen

• 3D shape

• http://micro.magnet.fsu.edu/primer/virtual/virtual.html

• http://www.mos.org/sln/SEM/gallery.html

Transmission Electron Microscope

• TEM

• Allows to see inside of cell

• Electrons pass through instead of light

• http://nobelprize.org/physics/educational/microscopes/tem/

Size Comparison

Prokaryote vs. Eukaryote

• With the invention of microscopes, scientists could see two groups of cells

• Prokaryotes

• Eukaryotes

Prokaryote

• 1-10 m in diameter

• NO membrane-bound organelles

• 1 circular DNA molecule located in nucleoid region

• Plasma membrane, cytoplasm & ribosomes

• Most have a cell wall (peptidoglycan)

• May have a polysaccharide capsule

–Ex. bacteria & cyanobacteria

Prokaryotic Cell

Eukaryote• 10-100 m in diameter • Nucleus & other membrane-

bound organelles• 2 or more linear DNA

molecules located in nucleus• Plasma membrane,

cytoplasm & ribosomes some have a cell wall (cellulose or chitin)

Ex. plants, animals, fungi, protista

Animal Cell

Animal Cell

Plant Cell

QUESTIONS?????