Chapter 2 section 2 (2011)

Chapter 2: Section 2
(Viewing Cells)
III. Viewing Cells
1

A. Early Microscopes
1. Microscope: A scientific instrument designed to
see things to small to view with the naked eye.
2. Uses lenses to make objects APPEAR larger than
then normal size.
3. In the mid 1600’s Anton Van Leeuwenhoek made
a simple microscope with one lens.
a. He witnessed seeing small things in pond water never
before seen.
2

B. Types of Lenses Used in Microscopes
1. CONVEX LENS: lens that looks like a teardrop
and magnifies.
a. Used in microscopes and glasses for farsightedness.
2. CONCAVE LENS: Lens that looks like an hourglass
and bends light inward; good for looking at far
away objects.
a. Used in telescopes, binoculars, and glasses for
nearsightedness.
3

C. Types of Microscopes
1. Simple Microscope: has 1 lens, similar to a
magnifying glass.
2. Compound Light Microscope:
a. Usually has 2 or 3 lenses inside of them; 1 in the
eyepiece, one in the tube, and one in the objective.
b. To find total magnification you must multiply the
power of the lenses.
c. Because there is an odd number of lenses the image
will be upside down and reversed.
d. This is the type we use in our school.
e. Stereo Microscope: View through two eyes and
produces a 3-D image.
6

3. ELECTRON MICROSOPES: Use a magnetic
field in a vacuum to direct beams of electrons
to view objects to small to otherwise be
seen; electron microscope images must be
photographed or electronically produced.
a. Scanning Electron Microscope (SEM): produces
a 3-D image of the surface of a cell; magnifies
around 200,000 X.
b. Transmission Electron Microscope (TEM):
Produces a 2-D image of a thinly sliced specimen;
magnifies up to 1,000,000 X.
7

D. How to Find Total Magnification (Our Microscopes)
1. LOW POWER – Eyepiece (10x) X Obj. lens (4x) = 40 X
2. MEDIUM POWER – Eyepiece (10x) X Obj. lens (10x) = 100 X
3. HIGH POWER – Eyepiece (10x) X Obj. lens (40 x) = 400X
4. THE COMPOUND LIGHT MICROSCOPE CAN
MAGNIFY UP TO 2000 x.
15

E. Parts of the Compound Light Microscope
1. Eyepiece: Part you look through, has a
magnification of 10X.
2. Coarse Adjustment Knob: Usually the larger of
the two knobs; use this first to bring the object
into rough focus.
a. Use only under low and medium power!!!!
3. Fine Adjustment Knob: Smaller of the two
knobs; used to bring the object into “perfect”
focus. (always use this last)
4. Arm: used to carry the microscope.
17

5. Revolving Nosepiece: The knob that moves the
objective lens into place.
6. High Power Objective Lens: Largest objective
lens, has a magnification power of 40X; always
used last in focusing.
7. Medium Power Objective Lens: Middle
objective lens in terms of size; has a
magnification power of 10X. (Use this after the
low power has been focused)
8. Low Power Objective Lens: Shortest Objective
lens; has a power of 4X. (Use this first when
focusing on the object)
18

9. Stage: Place where the slide is placed.
10. Stage Clips: Holds the slide in place.
11. Diaphragm: A disc that regulates the amount of
light hitting the object.
12. Base: Bottom of microscope; used to carry
microscope with arm.
13. Light/Mirror: Illumination source for the
microscope. (Provides light to view the object)
14. Revolving Nosepiece: Holds and turns the
objectives into viewing position.
15. Body Tube (Eyepiece Tube): Connects the
eyepiece to the revolving nosepiece.
19

F. Other Tools for Microscope Use:
1. Slides: Glass or plastic where specimen is placed.
2. Coverslip: glass or plastic placed over the
specimen to secure the object.
a. Coverslip should be placed onto the slide on a 45
degree angle and pushed down to force out air
bubbles.
20

G. Rules of the Microscope
1. Always carry the microscope holding the arm
with one hand and supporting the base with the
other hand.
2. NEVER touch the lenses with your fingers!!!!
3. The coarse adjustment know is used only when
looking through the lowest power objective
lens!!!
4. The fine adjustment knob is used when the high
power objective is in place
5. Cover the microscope when you store it!!!
Do not copy this slide…we will discuss it!!!
21

H. How to Use a Microscope
1. Place the microscope on a flat surface that is clear of
objects. The arm should be toward you.
2. Look through the eyepiece. Adjust the diaphragm so
light comes through the opening of the stage.
3. Place a slide on the stage so the specimen is in the
field of view. Hold it firmly in place by using the
stage clips.
4. Always focus with the coarse adjustment and low
power objective first!!
5. After the object is in focus on low power, turn the
nosepiece until the high power objective is in place.
6. Make sure the specimen is centered before changing
powers!!
7. USE ONLY THE FINE ADJUSTMENT TO FOCUS WITH
THE HIGH POWER OBJECTIVE LENS!!!
22

I. Making a Wet Mount Slide
1. Carefully place the item you want to look at in
the center of a clean, glass slide. Make sure the
sample is thin enough for light to pass through it.
2. Use a dropper to place one or two drops of water
on the sample.
3. Hold a clean cover slip by the edges and place it
at one edge of the water. Slowly lower the
coverslip (45 degree anlge) onto the water until it
lies flat.
4. If you have too much water or a lot of air
bubbles, touch the edge of a paper towel to the
edge of the coverslip to draw off extra water and
draw out unwanted air.
23

5. Sometimes Stain(Iodine) is used to make hidden
cell parts visible.
a. Other stains besides iodine are used in the science
world.
24

J. History of The Cell Theory
1. 1665 Robert Hooke was the
first person to see cells under
the microscope.
a. Hooke looked at a thin slice of
cork and saw these empty little
boxes which he called cells.
(because they looked like little
rooms)
Good looking Guy!!!!
25

2. In the 1830’s Matthias Schleiden studied plants
and found they also had these little cells.
3. The same year Theodore Schwann discovered
animals had cells!!!
4. Several years later Rudolf Virchow observed cells
dividing and proposed that cells come from other
cells that already exist.
5. These 4 Scientists are responsible for the ell
theory.
26

K. The Cell Theory:
1. All living organisms are made up of one or
more cells.
a. An organism can be one cell or many cells like most
plants and animals.
2. The cell is the basic unit of organization in
organisms.
a. Even in complex organisms the cell is the basic unit of
structure and function.
3. All cells come from other cells.
a. Most cells can divide to form two new identical cells.
27

Chapter 2 section 2 (2011)

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Chapter 2 section 2 (2011)