Lab Practical 1

Magnifying power of the ocular lenses

10x

Wet mount: how to make one correctly to minimize air bubbles.

A microscope slide specimen is suspended in a drop of liquid located between the slide and coverslip. -The refractive index of water improves the image quality. -Water helps support the specimen. To make a wet mount place a sample on the slide. Using an eyedropper put a drop of water on the sample. Place one end of the cover slip on the slide and slowly lower the other end using the end of a toothpick. This will help to prevent air bubbles from getting trapped under the cover slip.

Ways to adjust the light intensity on the microscope

Adjust the condenser and the light intensity for the greatest amount of light. With low power objectives, you might want to reduce the light intensity or shut the condenser to have a clear image.

Define field of view and how its size (diameter) is related to magnification.

Field of view is illuminated circular area that you see when you look into the microscope. Field of view decreases as magnification increases.

Differentiate between flagella of eukaryotes, flagellated algae, and filamentous algae.

Flagellated algae: euglenoid shape and swim by themselves. Filamentous algae: long chains.

Define Parfocal

Good quality microscopes are parfocal which means that the image will remain in focus when changing from a lower-power objective to a higher-power objective.

Name the objective lenses

Low-power: 10x, High-dry: 40x, and Oil immersion: 100x.

Define characteristics of Fungi, especially the molds and yeasts seen in lab.

Molds: multicellular, contain a hyphae. Yeasts: unicellular and lack a hyphae.

Know the proper procedure for focusing the microscope:

On the low-power objective, use the coarse objective only. When higher power objectives are used, the fine adjustment knob can be changed to bring the object into focus.

What is the relationship of resolution lens to magnifying power?

Resolution decreases with an increasing magnification.

Bacterial shapes

Rod (bacilli), Sphereical (cocci), Spirals

Fungi (molds and yeasts) grow on Sabouraud's Dextrose Agar. Why do fungi grow better on SDA than TSA or NA?

SDA is specific to fungi, because the medium is slightly acidic; fungi grow better in an acidic environment than bacteria do.

How to determine total magnification

Take the power of the objective lens and multiply it by the ocular lens (usually 10x)

Explain the fine adjustment knob

The fine adjustment knob is used for focusing finer details of a specimen being viewed. Used at only higher powers.

What is the function of immersion oil

The oil, which has the same refractive index as glass, directs more light onto the lens by limiting the loss of light. Once the microscope has been brought into focus at one magnification, the oil immersion lens can be rotated into position without fear of striking the slide.

Define resolution (resolving power).

The resolving power of a lens is its ability to completely separate two objects in a microscopic field.

How do you maximize resolution?

The shorter the wavelength of light, the higher the resolution. *Use blue filter.

Know the pitfalls of using the High-dry lens (40X)

To proceed from low-power to high-power, all that is necessary is to rotate the high-dry objective into position and open up the diaphragm. It may be necessary to make a minor adjustment to the fine adjustment knob to sharpen the image, but the coarse adjustment knob should NOT be touched.

Know how to use the oil immersion lens (100x), its resolving power, how it reduces light scatter.

Using oil reduces light diffraction and maximizes the numerical aperture to improve the resolution. The use of oil in this way enhances the resolving power of the microscope.

Define working distance and what is its relationship to lens power (magnification)?

as the power of the objective lens increases the working distance decreases

How does closing the iris diaphragm affect image brightness and contrast?

decreases brightness and increases contrast

What does parfocal lens system mean? Define parfocal.

term that means that a microscope's focus stays fairly constant when changing from one objective to another