Microbio lab quiz 1

The area being magnified by a high power objective is smaller due to the objective being closer to the specimen, thus the total light entering the objective is a fraction of the light that would be visible from the much larger area (field-of-view) that can be observed using lower power objectives.

Decreasing the area, decreases the amount of light per area so the image is dimmer.

Epidemiology is the tracking of a disease as it spreads through a population. This allows for the study of disease characteristics, identifying risk factors, identifying the index case and possibly the pathogen itself.

Define epidemiology.

Resolution: the smallest distance between two objects at which the objects still appear distinct. Parfocal: an arraignment of objective lenses so that when one objective lens is in focus, the other objective lenses can be rotated into position with minimum refocusing. Refraction: the alteration of a light path as it transits from one material to another - different material will slow the propagation of light by different degrees (i.e. different refractive index) - this causes the light path to bend.

Define the following terms: • Resolution • Parfocal • Refraction

Total magnification / Ocular power = Objective power 400/10 = 40x

If an object was magnified 400X using a 10X ocular lens, what would be the magnification of the objective lens? Please show your work

60%

If using hand sanitizer containing alcohol, what percentage of alcohol is recommended by the Center for Disease Control and Prevention?

Through vectors (biological agents that are either infected with the pathogen or mechanically transfers the pathogen)Aerosol dispersalContact with bodily fluids (blood, semen, lymph)Drinking/eating contaminated water/food

Name 3 ways that infectious diseases can be spread (transmitted).

These lab safety requirements are absolutely mandatory: Full safety glasses or goggles Aprons or long lab coats Gloves (nitrile is latex-free and holds up better than latex or vinyl) Closed shoes (sandals, crocs, or any type of shoe with openings or thin mesh are not allowed) No use of cell phones or other electronics in lab No eating or drinking in lab

Name three lab safety rules.

Minimum time is 20 seconds.

The Center for Disease Control and Prevention advises that you should wash your hands for how long in order to cut down disease transmission?

You should not wash your hands if you do not have clean water available or if the soap or detergent you are using is contaminated.

Under what situations would a person not want to wash their hands?

Ebola virus = BSL 4 E. coli = BSL 1

What are the biosafety levels for: Ebola virus E. coli

Most microscopes that you will encounter will be parfocal, thus only slight refocusing should be necessary when switching from the low power objective used to roughly focus the specimen to higher power objectives. Because higher power objectives will have a very shallow depth-of-field, you will need to have very fine control over the focus in order to keep your specimen in focus and to examine the specimen throughout its thickness. Using the course adjustment with higher power objects, with their smaller working distances, runs the risk of accidently crashing the objective into the slide.

What are the reasons why you should not use the coarse focus when using the 40X lens?

Severity of the disease, availability of treatment, and mode of transmission.

What are the three factors used to determine the assignment of biological agents to the appropriate biosafety level?

Collection of microorganisms that originate from one mother bacteria.

What is a bacterial colony? (Note that this question differs from the lab manual)

A pathogen is a microbe that causes disease. Disease it the disruption of homeostasis. Pathogens my be communicable or non-communicable.

What is a pathogen?

The main purpose of a coverslip is to confine the specimen to a thin plane, helping to keep objects in the specimen within roughly the same focal plane. This also helps with live, motile organisms by eliminating the z-axis of movement; they will mostly be confined to moving along the x and y axes; this will aid in tracking the organism and focusing. Other functions of a coverslip are to protect the specimen and objective in the even the objective crashes into the coverslip; to allow the use of immersion oil for living specimens; to preserve specimens after they have been fixed (prepares slides); to prevent the specimens from drying out (usually not a problem in microbiology since we are viewing fix/dead/dry specimens.

What is the main purpose of a coverslip?

Ocular power X Objective power = Total magnification (6)(30) = 180x

What is the total magnification of an object using a 6X ocular and 30X objective lens? Please show your work.

The light intensity knob /dimmer / rheostat controls the total amount of light, the iris/diaphragm controls the aperture through which this light can pass, and the condenser lens focuses this light onto the specimen.

What parts of the microscope affect the amount of light passing through the specimen? (Note that this question differs from the lab manual)

We use the 40x and 100x objectives to view bacteria since prokaryotes are particularly small. The 40x objective is the lowest power objective that will allow you to see the morphology and arrangement of bacteria. The 100x objective is preferred since it is powerful enough to show the finer details of bacteria. Note that "high power" and "oil immersion" are informal names for lenses and do not specifically refer to 40x and 100x objectives. Both are considered "high power" and other high power lenses (like 80x) also benefit from oil immersion".

Which 2 objective lenses do we use when viewing bacteria?

Stained specimens require more light than unstained specimens. The stain blocks out light, increasing contrast between heavily stained and lightly stained objects, but this will necessitate the use of more light to see details. Unstrained specimens block out very little light, so reducing light through the iris/diaphragm (preferred) or the dimmer/rheostat allows you to see the specimen with better contrast. This is in part because you eyes' pupils will not be as tightly closed due to excess light, reducing your ability to see contrast. In microscopy, we want to keep our pupils dilated so we get the most amount of light to our retinas through the widest aperture (your pupils).

Which is best viewed in low light: a stained specimen slide or an unstained live specimen slide? Why? (Note that this question differs from the lab manual)

The working distance is the distance between objective lens and the lens's focal plane (i.e. the plane where the specimen is in focus). The working distance decreases as the magnification power of the objectives increases - an inverse relationship.

Working distance decreases as magnification increases.