Discovering Cells
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Coulter
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Cells are the basic units of structure and
function in living things.
Cells and structure: structures of living things
are determined by the amazing variety of ways
in which cells are put together. (tree/dog)
Cells and function: the processes that enable it
to stay alive and reproduce.
Many and small: human skin cells, one square
centimeter of your skin’s surface contains more
than 100,000 cells.
An overview of cells
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The invention of the microscope made it
possible for people to discover and learn about
cells.
Microscope-is an instrument that makes small
objects look larger.
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Some do this by using lenses (like eye glasses) to
focus light.
Simple microscope- one lens
Complex microscope- more than one lens
First Observation of Cells
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1663 Hooke used his microscope to observe the
structure of a thin slice of cork
He thought what he saw looked like small
rooms, so he called them cells.
He described what he observed; “these pores,
or cells, were not very deep, but consisted of a
great many little boxes…”
He was amazed about how many cells there
were, he estimated that in 1 cubic centimeter
there were 1,200,000,000 cells “almost
incredible”
Robert Hooke
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Looked at drops of lake water, scrapings from
teeth and gums, and water from rain gutters.
Was surprised to find a variety of one-celled
organisms.
Noted that many moved, he called them
animalcules (little animals)
Anton van Leeuwenhoek
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Matthias Schleiden, Theodor Schwann, and
Rudolf Virchow.
In 1839, Schleiden concluded that all plants are
made of cells.
In 1840, Schwann concluded that all animals
are also made up of cells
This huge discover did not explain where cells
came from.
In 1855, Virchow proposed new cells formed
only from cells that already exist.
Development of the cell
theory
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Is a widely accepted explanation of the
relationship between cells and living things
All living things are composed of cells
Cells are the basic units of structure and
function in living things
All cells are produced from other cells
The Cell Theory
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The lenses in light microscopes magnify an
object by bending the light that passes through
them.
Observe a hand lens
What do you notice?
Lens is curved, thicker in the middle. A lens
with this curved shape is called a convex lens.
Light passes through the sides and the lens
bends inward. When this light hits the eye, the
eye sees the object as larger than it really is.
Magnification of Lenses
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Uses more than one lens.
Total magnification of the lens is equal to two
lenses multiplied together.
Example: first lens makes object 10 times larger.
The second lens makes the object 40 times
larger.
10x40=400
Compound microscope
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The ability to clearly distinguish the individual
parts of an object is called resolution
sharpness, of an image
Resolution
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Electron microscopes use a beam of electrons
instead of light to produce a magnified image.
Electrons are tiny particles that are smaller than
atoms.
Can see smaller images than those of light
microscopes.
Resolution is much better than light
microscopes.
Electron microscope
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Problem: How can you build a compound
microscope?
Materials:
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2 dual magnifying glasses, each with one highpower and one low-power lens
Metric ruler
Black construction paper
tape
Build a microscope
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Work with a partner. Using only you eyes, examine
words in a book. Then use the high-power lens to
examine the same words. In your notebook write
your observations.
Hold the high-power lens about 5 to 6 cm above the
words in the book. When you look at the words
through the lens, they will look blurry.
Keep the high-power lens about 5-6cm above the
words. Hold the low-power lens above the highpower lens. Write your observations.
Move the low-power lens up and down until the
image is in focus and upside down.
Build a microscope
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One the image is in focus, experiment with raising
and lowering both lenses. Your goal is to produce
the highest magnification while keeping the image
in clear focus.
When the image is in focus at the position of highest
magnification, have your lab partner measure and
record the distance between the book and the highpower lens. Your lab partner should also measure
and record the distance between the two lenses.
Write a description of how the magnified words
viewed through two lenses compares with the
words seen without magnification.
Build a microscope
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Based on what you learned in part 1, work with
a partner to build your own microscope.
Sketch your design in lab report.
Test your microscope by examining a chosen
living and non-living organism from outside.
Write down observations. Draw to the best of
your ability what you see.
Build a microscope