The Cell Theory

1
The Cell Theory

• And how it developed

2
Problem Cells are small

• Most cells are too small to be seen without
  magnification.
• Look at your hand? Do you see cells?

3

• Sizes of cellular components

4
Solution Magnification

• Simple magnifiers drop of water or glass bead.

5
Compound magnification

• First microscope invented by Zacharias and Hans
  Janssen in the 1590's
• Uses a series of lenses to make larger images

6
Microscopes

• Various styles of
• microscope
• were developed
• by mid 1600s,
• mostly to
• examine cloth

7
Robert Hooke - 1665

• First recorded examination of biological
  material with microscope
• Looked at slices of cork
• Described structure as
• cells

8
Hookes observation
9
Hookes observations

• Cork was long-dead
• material saw remains of
• cell walls only.
• Later examined fresh plant
• tissue saw fluids inside.

10
Impact

• Cells are the basic structural unit of living
  things.

11
Anton Von Leeuwenhoek

• Good amateur microscope maker.
• 1668 - Examined pond water with microscope
• saw freely moving beasties or animalcules.

12
Von Leeuwenhoek

• Also examined blood.
• First to observe single-celled organisms in
  tooth debris.

13
Von Leeuwenhoek

• Considered
• the father
• of
• microbiology

14
Impact

• A single cell can perform all life
• functions.

15
Henri Dutrochet - 1824

• Proposed that all living things were made of
  cells.
• based on observations of many organisms.

16
Technology 1820s on

• Development of staining techniques improves
  visibility of cellular structure.
• unstained tissue mostly clear.
• Special chemical reactions can show structures,
  enzymes, whole cell shape, etc.

17

• Staining makes bacterial cells stand out.

18
Robert Brown - 1831

• Realizes that all cells have a dense region in
  the center.
• Calls it a nucleus.
• Function unknown.

19
Matthias Schleiden - 1838

• Observed many plant samples
• Concluded that
• all plants are
• made of cells

20
Theodor Schwann - 1839

• Observed many
• animal samples
• Concluded that all animals are made of cells.

21
Johannes Purkinje - 1839

• Reported that all cells he observed were filled
  with jelly-like substance.
• Named this substance protoplasm.
• assumed to have special life-giving
  chracteristics.

22
Impact

• All living things are made of cells

23
Rudolph Virchow - 1855

• Observed cells dividing.
• True in plants and animals

24
Impact

• All cells come from pre-existing cells

25
Cell Theory late 1800s

• All living things are made of cells and cell
  products.
• All cells carry on life activities. Life
  activities of multicelled organisms are combined
  product of all cells.
• New cells arise only from other cells by the
  process of cell division.

26
Technology improves

• 1939 Electron microscope allows much greater
  magnification.
• Uses electrons, rather than light.
• Allows much greater resolution, too.
• Specimens must be exposed to vacuum, so not good
  for living things.

27
Getting information from an image

• Magnification tells how many times bigger the
  object appears. Bigger is easier to see.
• Resolution tells how much detail is available in
  the image.
• A bigger image with poor resolution is useless!

28
Electron Microscope
29
Scanning Electron Microscope

• Bounces electrons off surfaces without
  penetrating.
• Produces very detailed 3-D view of surface.
• No internal structure!

30
SEM Images
31
Transmission Electron Microscope

• Maximum magnification can see large molecules!
• Electrons pass through very thin (0.2mm) slices
  of an object and are detected on a screen.
• Allows examination of structures within cells.

32
TEM Image
33
Compound Light Microscope

• Light passes up from the base and is focused
  through a diaphragm. It passes through the
  specimen, and a series of lenses in the objective
  magnify the specimen.
• Lenses in eyepiece provide a magnified view of
  the first image.

34
The specimen

• The object to be observed is placed on a glass
  slide.
• Must be thin and clear enough for light to pass
  through.
• It must be covered with water or another clear
  liquid.
• A thin cover glass is placed over the object and
  liquid.

35
Illumination

• Different types of illumination can emphasize
  different features of the specimen.
• Can be combined with special stains UV light
  with fluroescent stains or labels for particular
  types of materials.

36
Types of Light Microscopy
37
Stereomicroscope

• A stereo or dissection microscope is a low power
  light microscope. Good for magnifying objects
  and getting a three dimensional view of surfaces.
  
• Light can bounce off the surface of the specimen,
  be transmitted through it, or both.
• You cannot typically see individual cells
  because of the low magnification, and because the
  objects are too thick for good resolution.

38

• A stereo microscope
• Note the 2 light sources
• From above, or epi-illumination
• From below, or transillumination

39
Stereomicroscope

• Also called a dissecting microscope, it is most
  useful for magnifying objects while they are
  being manipulated.

40
What to use?

• What type of microscope you use depends on what
  information you need.
• May use a stereomicroscope to obtain a tissue
  sample, a light microscope to look at the tissue,
  and transmission electron microscope to learn
  about the details within the cells.