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Chapter 2, Section 3
Discovering Cells
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An Overview of Cells
 Cells:
 Cells
the basic units of
structure and function in
living things
and Structure
How cells are put together
and the shape that forms
 Cells
and Function
Obtaining oxygen, getting
rid of wastes, obtaining
food, and growing
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First Observations of Cells
 1590
 The
invention of the
microscope made it possible
for people to discover and
learn about cells
 Microscope:
an instrument that
makes small objects look
larger
SIMPLE MICROSCOPE: one lens
 COMPOUND MICROSCOPE:
more than one lens
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Robert Hooke
 One
of the first people to observe cells
 Built
his own compound microscope
 Used
this microscope to observe thin slice of
cork
 Looked like tiny rectangular rooms, called
them cells meaning “small rooms”
+ Anton van Leeuwenhoek
 About
 Built
the same time as Hooke
a simple microscope
 Used
this microscope to observe
lake water, scrapings from teeth
and gums, and water from rain
gutters
 He
noticed that many of the things
he observed were ONE-CELLED
 He
called the moving organisms
he saw
 ANIMALCULES
(“little animals”)
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Development of the Cell Theory
Three scientists worked together…
 Schleiden

Concluded all plants are made of cells
 Schwann
 Concluded
that all animals are also made of cells
 THEREFORE, all living things are made up of
cells
 Virchow
 New
cells are formed only
from cells that already exist
 “All cells come from cells”
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The Cell Theory
 The
cell theory is a widely accepted explanation
of the relationship between cells and living
things
1.
All living things are composed of cells
2.
Cells are the basic units of structure and
function in living things
3.
All cells are produced from other cells
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Magnification and
Lenses
 Lenses
in light microscopes magnify an object
by BENDING the light that passes through them
 Convex
lens: magnifying glass and
hand lenses
 Middle
of lens is thicker
 Outside of lens is thinner
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Compound Microscope
Magnification
 Lenses
of a LIGHT microscope…
 Light
passes through specimen
 Then through two lenses
 1st lens near specimen magnifies object
 2nd lens near the eye further enlarges object
 Example:
 One
lens makes an object 10 times larger,
second lens makes an object 40 times
larger
 TOTAL: 10 X 40 = 400
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Resolution
 Being
able to clearly distinguish the individual
parts of an object
 Or…sharpness
of an image
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Electron Microscope
 Electron
microscope uses a beam of electrons
instead of light to produce a magnified image
 The
resolution is much better than the resolution
of a light microscope