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Describe the position of your hands when carrying the microscope to and from your lab bench?
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Differentiate between the limit of resolution of the typical light microscope and that of the unaided human eye?
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Microbiology Lab
Lab Test 1 part 1
| Question | Answer |
|---|---|
| Describe the position of your hands when carrying the microscope to and from your lab bench? | Answer: One hand should be under the base of the microscope to support its weight and one hand should be on the arm for balance. |
| Differentiate between the limit of resolution of the typical light microscope and that of the unaided human eye? | Answer: the limit of resolution of the unaided human eye is about .2 mm. for the typical light microscope, the limit is .2 um. |
| What two adjustments can be made to the condenser? what effect do these adjustments have on the image? | Answer: the condenser high and diaphragm can be adjusted. illumination of the specimen is increased when the condenser is raised and the diaphragm is opened. |
| Why are condenser adjustments generally preferred over the use of light intensity control? | Answer: unlike the voltage control, condenser adjustments will increase illumination without affecting the bulb life. |
| When using the oil immersion lens what four procedures can be implemented to achieve the maximum resolution? | Answer: the maximum resolution with the oil immersion lens is achieved by using a layer of oil, using a blue filter over the light source, raising the condenser to its highest point, and opening the condenser diaphragm. |
| Why is it advisable to start first with the low power lens when viewing a slide? | the oil immersion lens has the smallest working distance and one runs the risk of striking the slide with the lens when trying to achieve focus. |
| Why is it advisable to start first with the low power lens when viewing a slide? Part 2 | starting with the low power lens, which has a larger working distance, and progressing up to the oil lens is advised. |
| What is the relationship between the working distance of an objective lens and its magnification power? | Answer: as the power of the objective lens increases the working distance decreases. |
| As the power of the objective lens increases the working distance decreases? | Answer: oil immersion |
| This objective lens provides the second highest magnification? | Answer: high dry |
| This objective lens provides the lowest magnification? | Answer: low power |
| This objective lens has the shortest working distance? | Answer: oil immersion |
| The coarse focus knob should be adjusted only when using this objective lens? | Answer: low power |
| This lens collects and focuses light from the lamp onto the specimen on the slide? | Answer: condenser |
| This lens, aka eyepiece, often comes in pairs? | Answer: ocular |
| Diopter adjustments can be made to this lens? | Answer: ocular |
| A diaphragm is used to regulate light passing through this lens? | Answer: condenser |
| Acetone is the safest solvent for cleaning an objective lens. | False |
| Only lint free, optically safe tissue should be used to wipe off microscope lenses | True |
| The total magnification capability of a light microscope is only limited by the magnifying power of the lens system | False |
| The coarse focus knob can be used to adjust the focus when using any of the objective lenses. | False |
| Once focus is achieved at one magnification, a higher power objective lens can be rotated into position without fear of striking the slide. | True |
| The resolving power of a microscope is a function of: | Answer: the numerical aperture of the lens and the wavelength of light |
| The coarse and fine focus knobs adjust the distance between: | Answer: the stage and the objective lens |
| A microscope that maintains focus when the objective magnification is increased is called: | Answer: parfocal |
| The total magnification achieved when using a 100x oil immersion lens with a 10x binocular eyepiece is: | Answer: 1000x |
| The most useful adjustment for increasing image contrast in low power magnification is: | Answer: closing down the diaphragm |
| Before the oil immersion lens is rotated into place, you should: | Answer: center the object of interest in the preceding lens and place a drop of oil on the slide |
| For which types of specimens is dark field microscopy preferred over brightfield microscopy? | Darkfield microscopy is preferred for live unstained specimens or thin cells like spirochetes that are difficult to resolve by staining and brightfield microscopy. |
| If a darkfield condenser causes all light rays to bypass the objective, where does the light come from that make an object visible in a dark field? | Reflection of oblique rays off of objects passes through the lens system. |
| Staining cell is often performed to enhance images acquired by brightfield microscopy. Phase contrast microscopy does not require cell staining. Why is this advantageous? | Staining kills live cells and does not allow observation of movement. |
| As light passes through a transparent object, how are direct and diffracted light rays produced? | Direct rays are produced when light passes straight through a transparent medium without changing amplitude or phase. |
| How much phase shift occurs? | Diffracted rays are produced when light is bent during retardation by the medium due to density differences and are phase-shifted ¼ wavelength. |
| A phase contrast microscope differs from a bright field microscope by having a? | Answer: diaphragm with an annular stop and phase plate in the objective lens. |
| Which of the following would be the best observed for a bacterial cell using phase contrast microscopy? | Answer: motility of cells |
| The phase contrast microscope is best suited for observing? | Answer: living organisms on a slide with a cover glass. |
| What is quenching? | Quenching occurs when fluorescence of a molecule diminishes during prolonged exposure to UV light. |
| Describe two hazards associated with the use of mercury vapor after lamps. | Direct exposure to light from mercury vapor arc lamps can damage eyes and the pressurized gas creates the potential to explode. |
| What are two advantages of using darkfield condenser for florescence microscopy? | A darkfield condenser provides the best contrast and it deflects the majority of UV rays, which protects the viewer’s eyes. |
| Specific proteins on or in a cell can be tagged with fluorochromes that has been chemically linked to | antibodies |
| before reaching the ocular the light generated by the mere try vapor are lamp travels through | heat filter, exciter filter, condenser, slide, objective lens and then the barrier filer. |
| the barrier filter in the fluorescence microscope is kept in position to | screen out exciting light rays |
| how do you know your transfer to a broth was unsuccessful? how do you know your transfers in agar slants were successful? | Success is presence of growth. |
| if any of your transfers were unsuccessful suggest possible errors that may have been mad in the transfer process? | Failure is no growth; or growth of a wide variety of colonies, signaling contamination. |
| provide three reasons why the use of aseptic technique is essential when handling microbial cultures in the lab | When handling microbial cultures, aseptic technique limits contamination of yourself and your workspace with the microbes in the cultures, and it limits contamination of your cultures with unwanted environmental microbes. |
| provide two examples of how heat is used during inoculation of tube culture? | The flame from a Bunsen burner is used to sterilize transfer instruments (e.g., inoculating loop) and is used to flame the opening of the tube after the cap is removed and before the cap is replaced. |
| how is air contamination prevention when an inoculating loop is under to introduce or take bacteria sample to/from an agar plate? | Since the opening of a plate is not readily flamed, one should hold the lid over the top of the open plate when inoculating so that air contamination is limited. Working near a flame is also useful. |
| where should a label be written on an agar plate | Labels should be written on the bottom of the agar plate. |
| how should agar plates be incubated? why? | Agar plates should be incubated in an inverted position to prevent condensation on the agar surface that could spread the inoculated organisms. |
| disinfectants are effective against which types of organisms? which types of organisms may remain on the lab bench even after disinfection? What disinfectant is used in your lab? | Disinfectants, such as bleach and alcohol, are generally useful against vegetative cells and viruses but may not completely eradicate bacterial endospores. |
| 7.1 compare and contrast the growth of bacteria in different physical types of media | The presence of growth in a liquid media such as a broth is indicated by turbidity or cloudiness. Individual colonies are not visible and one species could not be separated from another. |
| 7.2 what might be the advantages and disadvantages of using each type | Solid media such as slants allow for visible growth on the surface that can be observed for color and texture, etc. Plates allow for isolated colony growth, where one species could be separated from another if colonies are isolated and subcultured. |
| a disinfectant is used on your work surface | before the beginning of lab procedures. after all work is complete. after any spill or live microorganism |
| to retrieve sample from a culture tube with and inoculating loop the cam of the tube is | remove and held with fingers of the loop hand |
| an inoculating loop or needle is sterilized using heat | entire wire is bright red |
| which of the following would be a correctly labeled agar plate | S. aureus on the bottom |
| do your slants contain pure cultures? how would you confirm their purities? | Staining and microscopy or a streak plate can determine purity of a culture. |
| define term colony as it relates to bacterial growth on a solid media | A colony is a visible microbial growth on a solid medium that originated from a single parent and through cell division produced a multitude of identical daughter cells. |
| what colony characteristics can be used for differentiation of bacterial species?as an exp compare the properties of colonies of serrate marcescens and micrococcus letters on your streak plate | Useful colony characteristics for differentiation of bacterial species include size, color, shape, texture, opacity, and odor. OMIT any mention of Micrococcus luteus (we did not work with this). |
| why is dilution a necessary part of pure culture preparation? | When working with culture that may contain millions of cells, dilution on to a solid medium is essential for separating the cell with enough space so that they grow into isolated colonies. |
| what advantages does the streak plate method have over the pour plate method | The streak plate method does not require any additional media for dilution and only requires one plate for inoculation. |
| what advantages does the pour plate method have over the streak plate method | The pour plate method requires less skill, has optimization built in, and will more likely produce the desired result. |
| why is the loop flamed before it is placed in a culture tube? why is it flamed after completing the inoculation | The loop is flamed before entering a culture tube to ensure that no contaminating microbes are introduced into the culture. The loop is flamed afterward so that no culture microorganisms are introduced into the working environment. |
| 8.1 explain why plates should be inverted during incubation? | Plates are inverted during incubation so that moisture does not accumulate on the lid and drop on to the agar surface. |
| 8.2 explain why plates should be inverted during incubation? | This will cause the organisms to spread and negate the dilution effect. Also, agar plates tend to dehydrate faster in the upright position. |
| how does smear preparation of cells from a liquid medium differs from preparation of cells from a. solid medium | To prepare cells from solid media, cells must be mixed in 1–2 drops of water on the slide. Two to three loopfuls of cells from liquid media can be transferred directly to the slide. |
| why is it important to limit the quantity of cells used to prepare a smear | Large amounts of cells in a smear can cause staining artifacts because the stain is not washed away from thick areas by destaining agents or water. Remember, a little bacteria goes a long way in making a nice thin smear! |
| describe the potential consequences of making a smear that is too thick | In differential stains such as the Gram stain, results can be inaccurate due to trapping of the stain in areas where the smear is too thick. |
| for prep of a smear on a slide what is purpose of heat fixation? what problems can arise when the slide is heated in a flame? | Heat fixation causes cells to adhere to the slide during staining. However, structures such a capsules can undergo shrinkage during heat fixations and be lost in staining procedures. For that reason, capsule stains are not normally fixed. |
Created by:
zachflemings