BIO 390 Advanced Exam Material – Microbiology, Viral Replication, Immunology, Pathogenic Infections, Practice Questions

This resource compiles advanced exam questions and correct answers for BIO 390, focusing on virology, immunology, and pathogenic microorganisms. It explains viral replication, host-pathogen interactions, and the mechanisms of microbial diseases. A verified and updated guide, it is highly useful for detailed microbiology exam preparation. What is the primary use of slants? - answerTo provide a solid growth surface that is easier to store/transport. What is the primary use of deeps? - answerTo allow anaerobic bacteria to grow. What is the primary use of broths? - answerTo grow large numbers of bacteria in a small space. Can we determine whether a broth culture is pure by visually inspecting it without a microscope? - answerNo Can we determine whether a deep culture is pure by visually inspecting it without a microscope? - answerNo Can we determine whether a slant culture is pure by visually inspecting it without a microscope? - answerNo When is a loop preferable for transferring bacteria? - answerA loop is preferable when transferring cultures to a slant or a broth. When is a needle preferable for transferring bacteria? - answerA needle is preferable when making deep cultures. What is the purpose of flaming the loop before use? - - 2 -: answerTo sterilize the loop from environmental microbes. What is the purpose of flaming the loop after use? - answerTo sterilize the loop from cultured microbes. Why must the loop be cool before you touch it to a culture? - answerA hot loop would heat up the bacteria enough to denature and kill the microbes. Should you set the loop down to let it cool? - answerYou should not set the loop down to cool because that would contaminate it. Why is aseptic technique important? - answerMinimizes contamination and cross contamination. What evolutionary advantage would there be to the formation of a pellicle in a liquid medium by a bacterium? - answerIt would provide oxygen-loving bacteria with the ability to float on the surface of the liquid and form aerobic colonies. How can you tell that the media provided for this exercise were sterile? - answerThere was no growth prior to the transfer of bacteria. The broth was clear and not turbid. Why is it desirable that microscope objectives be parfocal? - answerBecause parfocal microscope objectives remain focused when magnification is changed, so you can change lenses without losing focus. Which objective focuses closest to the slide? - answer100x oil immersion What controls the amount of light reaching the ocular lens? - answerIris diaphragm What effect does increased magnification have on the field of view? - answerAs the magnification increases, the field of view decreases. Name two ways in which you can enhance the resolving power. - answer1.) Use a shorter wavelength of light 2.) Increase numerical aperture What advantage does the low-power objective lens have over the immersion objective - 3 -: for viewing fungi? - answerIt provides a better view of the overall shape since fungi are significantly larger than bacteria. What would occur if water were accidentally used water in place of immersion oil? - answerThe image would not be clear because the immersion oil helps bend the light to focus correctly. Of what value is a simple stain? - answerA simple stain allows you to see the size, morphology, and arrangement of the cells. What is the purpose of fixing the smear? - answerTo prevent the sample from being lost during staining. In heat fixing, what would happen if too much heat were applied? - answerThe cells could be denatured and may lose their structural integrity, which would make them less viewable under the microscope. The glass slide could crack or melt with enough heat. Methylene blue can be prepared as a basic stain or an acidic stain. How would the pH effect the staining of bacteria. - answerThe bacteria can only be stained by a dye with a charge opposite their own. An acidic dye's negative charge would be repelled by the negative charges of the bacterial cell. Can dyes other than methylene blue be used for direct staining? - answerYes, any dye that can be prepared as a basic stain could be used because the stain can permeate the cell wall and adhere by weak ionic bonds to the negative charges of the bacterial cell. Bacteria can be seen without staining. Why then was Koch's recommendation for fixing and staining important for microbiology? - answerFixing kills the bacteria without distorting their shape. This allows us to see structure and later allowed us to see things like gram stain. What types of dyes are used for negative staining? - answerDyes with a negative charge, because they are repelled by the negative cell wall and dye the background - 4 -: instead of the cells. What microscopic technique gives a field similar in appearance to that seen in the negative stain? - answerDark field microscopy Carbolfuchsin can be used as a simple stain and as a negative stain. As a simple stain, the pH is ... - answerAlkaline India ink can give the appearance of a negative stain when used in a wet mount. What is the basis for this stain? (India ink is the suspension of 0.5 1.0 micrometer carbon particles in water.) - answerThe carbon particles are too large to enter the cell, so the background is stained instead - giving it the appearance of a negative stain. Why will old gram-positive cells stain gram-negative? - answerOld gram-positive cells will stain gram-negative because over time their cell walls degrade. Can iodine be added before the primary stain in a Gram stain? - answerNo, because iodine allows the crystal violet complex to be formed with the peptidoglycan of the cell wall. Which step can be omitted without affecting determination of the Gram reaction? - answerStep 4 - Safranin Suppose you Gram stained a sample from a pure culture of bacteria and observed a field of red and purple cocci. Adjacent cells were not always the same color. What do you conclude? - answerThe culture is old. Suppose you are viewing a Gram stained field of red rods and purple cocci through the microscope. What do you conclude? - answerThe culture is mixed or contaminated. Since you can't identify bacteria from a Gram stain, why might a physician perform a Gram stain on a sample before prescribing an antibiotic? - answerCertain antibiotics affect certain gram stain bacteria, but not both. It would be better to use an antibiotic that affects the specific gram stain bacteria rather than a broad spectrum antibiotic. If you Gram stained - 5