Date: September 28, 2015
Aim #10: What are some other tools scientists use in the
laboratory?
Do Now: Warm-Up Notebook
Date
9/28
Title of Activity
The Microscope
HW:
1)
2)
3)
4)
Complete practice questions- “Tools of Biologist”
Textbook HW #4 (Section 1-3) due Tuesday 9/29
Castle Learning assignment due Wednesday 11:59PM
UNIT 1 TEST- NEXT WEEK THURSDAY/FRIDAY
Page #
20
1. How do we prepare a wet-mount?



Place drop of water on slide
Place specimen in water
Place cover slip on a 45º angle
to avoid air bubbles
Microscopy: the use of microscopes to magnify an image for closer
observation
• Resolution: the clarity of the magnified image
• Permits close observation of fine details
Image from microscope
(magnification: 100 x)
Image from microscope
(magnification: 45 x)
Image from microscope
(magnification: 10 x)
Lower resolution
Lower resolution
Higher resolution
Higher resolution
Microscopes
1. Phase-contrast microscope


Light microscope that
enhances contrast
Useful in examining living,
unstained cells
2. Transmission electron
microscope
3. Scanning electron
microscope
Phase-contrast Microscope
• Microscope used for examining living things
• Enhances contrast
• Does not require staining
2. What is an Electron Microscope?

Uses beams of
electrons (NOT light
waves) to produce
magnified image

specially fixed and
treated and mounted in
a vacuum
How do they improve images?

High
magnification

High resolution:
the ability to
separate two
objects close
together
Electron Microscope
• Uses a beam of electrons instead of light
• Allows for magnifications of >100,000x with high resolution
Types of Electron Microscopes

Transmission Electron
Microscope (TEM)




Useful for studying interior of cells
Cannot view living specimen
Machine is very delicate and requires
special engineers
Machine is very expensive and costs
hundreds of thousands of dollars

Scanning Electron Microscope
(SEM)



Useful for studying surface of cells
Resulting images have a 3-D
appearance
Cannot view living specimen
Transmission Electron Microscope (TEM)
• Useful for observing cell interiors
• Expensive, complex machine converts information about the
electrons as they hit the specimen into a visual image.
• Preparing specimens for
TEM requires fixing,
dehydrating, and
sectioning the specimen
using elaborate
machinery
• Specimen must be cut
into very thin tissue
• Tissue is killed in
preparation
3. What is a stereoscope?

AKA: Dissecting Microscope

Binocular: two tubes

Presents a slightly different
view of specimen to each
eye… 3D

Useful for opaque objects
and small organisms or
body structures
4. What is a centrifuge?


AKA: ultracentrifuge
Separates according
to different densities
by spinning sample
in a test tube at very
high speeds
Ultracentrifuge
• Used for cell fractionation: separation and sorting of cell parts,
like organelles
• First, tissue is blended and mashed
• Produces a liquid called the homogenate
• Homogenate is centrifuged to sort the different parts by density
Freeze Fracture
• Used to study membranes under an electron microscope
• Involves freezing and cleaving the membrane into two halves.
• Each half is then coated with metal to make a cast which can then
be studied under the microscope.
5. Why do we stain cells?

Cell Structures
can be made
visible by
treatment with
solutions that
color certain parts
of cells and not
others
Tissue Cultures
• Used to study cells in vitro (in a lab) rather than in vivo (in a
living thing)
• Living cells are grown in a nutrient-rich medium
• Ex: agar
• Cells will reproduce and scientists can study each generation
using tools like a phase-contrast microscope
6. Why do we use indicators?
 Substances
that change
color when in
the presence
of certain
chemicals