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 1600’s,
mostly to
examine cloth

7. Robert Hooke
First recorded examination of biological material with microscope
Looked at slices of cork
Described structure as
“cells”

8. Hooke’s observation

9. Hooke’s observations
Cork was long-dead
material – saw remains of
cell walls only.
Later examined fresh plant
tissue – saw fluids inside.

10. Cells are the basic structural unit of living things.
Impact:
Cells are the basic structural unit of living things.

11. Good amateur microscope maker.
Anton Von Leeuwenhoek
Good amateur microscope maker.
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. A single cell can perform all life
Impact:
A single cell can perform all life
functions.

15. Proposed that all living things were made of cells.
Henri Dutrochet
Proposed that all living things were made of cells.
based on observations of many organisms.

16. Technology – 1820’s 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
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
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. All cells come from pre-existing cells
Impact:
All cells come from pre-existing cells

25. Cell Theory – late 1800’s
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. 1939 – Electron microscope allows much greater magnification.
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.