Date: September 28, 2015

Aim #10: What are some other tools scientists use in the laboratory?

HW:1) Complete practice questions- “Tools of Biologist”2) Textbook HW #4 (Section 1-3) due Tuesday 9/293) Castle Learning assignment due Wednesday 11:59PM4) UNIT 1 TEST- NEXT WEEK THURSDAY/FRIDAY

Do Now: Warm-Up Notebook

Date Title of Activity Page #9/28 The Microscope 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: 10 x)

Image from microscope(magnification: 45 x)

Image from microscope(magnification: 100 x)

Higher resolution

Lower resolution

Higher resolution

Lower 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