Cell Theory: Before Microscopes
• Before microscopes, most people believed in spontaneous generation (The belief that living things could arise from non-living matter).
1668: Francesco Redi attempts to disprove the spontaneous generation in maggots.
1745: John Needham attempts to prove spontaneous generation.
Attributes results to a “life force”
Spontaneous generation was
upheld until the mid-1800s.

• In 1859, Louis
Pasteur finally disproved the theory of spontaneous generation.

• Used a swan-shaped flask to show that if no microbes could get into the broth, nothing would grow
• What made his experiment good?
Controlled Variables
-
Same broth, light, temp .
Manipulated Variable
-
Whether or not microbes have access to broth
Responding Variable
-
Whether or not microbes grew
What impact do you think this had on medical practice.

The Development of the Microscope
• Explain the following statement:
“You may owe your life to the invention of the microscope.”
• 1595: The Janssen
Bros. invent the first microscope.
- It was compound
(2 lenses)

• 1665: Robert Hooke improves on the design
- Observes first tiny units of life and calls them “cells”

• Antoni van
Leeuwenhoek was the first person to see living cells.

Cell Theory: Gets It’s Start …
• 1839: M.J.
Schleiden, Theodor
Schwaan put forth a three part cell theory:
1) All living things are made up of one or more cells.

2) Cells are the smallest functional units of organisms (i.e. the organism’s needs are the cells’ needs).
Take in nutrients
- Use energy to do work (life processes)
- Get rid of wastes
- Maintain certain temperatures and chemical conditions (e.g. acidity)
Multi-cellular organisms are just cells working together to accomplish these basic tasks
Cell Tissue Organ System Body

3) All cells come from pre-existing cells through
the process of cell division. (not from spontaneous generation)

• The Compound Light Microscope
– Light passes through the specimen
– Lenses enlarge, or magnify, the image.
– micrometres ( μ) are used to measure very tiny objects. (1mm =
1000 μm)
(a) Light micrograph (LM) of a white blood cell (stained purple) surrounded by red blood cells

Magnification
• An increase in the specimen’s apparent size.
• To calculate the magnification of the microscope – ocular x objective
Power
Low
Medium
High
Ocular Lens
Magnification
10X
10X
10X
Objective
Magnification
4X
10X
40X
Total
Magnification
40X
100X
400X

Field of View (F.O.V.): The diameter of the circular region of the slide visible under the microscope
• the higher the magnification, the smaller the field of view.
Power Magnification F.O.V.
Low 40x
Medium
High
100x
400x
F.O.V.

Field of view can be used to estimate the actual size of objects actual size

F .
O .
V .
fit #


400
 m
95
4 .
2
 m

• The field of view under higher magnification can be less than 1mm.
• We can estimate by using the low magnification and
F.O.V. in a formula.

Example:
High F.O.V. (HP) = Low F.O.V. (LP) x LP magnification ÷ HP magnification
Example:
HP magnification = 40X
LP magnification = 4X
LP F.O.V. = 4500 µm
HP F.O.V. = 4500 µm x 4X ÷ 40X
HP F.O.V. = 4500 µm x 0.1
HP F.O.V. = 450 µm

Resolution
•
The ability to distinguish individual objects.
• The greater the magnification, the smaller the objects that can be resolved.

Contrast
• dark vs. bright
• phase contrast microscopes enhance contrast.

Staining
• used to increase contrast and to show specific parts of cells.
Nucleus is stained
Fluorescent Stains

•
– It uses a beam of electrons
– It has a higher resolving power than the light microscope

•
•
Human height
Length of some nerve and muscle cells
Chicken egg
Frog eggs
Plant and animal cells
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
Proteins
Small molecules
Atoms

SEM
• The scanning electron microscope (SEM) is used to study the detailed architecture of the surface of a cell
(b) Scanning electron micrograph (SEM) of cilia (above)
And a white blood cell

TEM
• The transmission electron microscope (TEM) is useful for exploring the internal structure of a cell
(c) Transmission electron micrograph (TEM) of a white blood cell & cilial

• Read page 510 of your textbook and complete the Instant Practice Problems
• Using page 508 of your textbook, completely label the microscope picture.