BIO D171 MICROBIOLOGY Module 3 Final Exam Review Q & A 2024 1. Which staining technique would be most appropriate for visualizing the capsule surrounding certain bacteria? A. Negative stain B. Gram stain C. Acid -fast stain D. Simple stain Answer: A. Negative stain Rationale: The negative stain technique uses a dye that stains the background but not the cells, making the capsule, which does not tak e up the stain, visible against the contrasting background. 2. When preparing a slide for Gram staining, what is the purpose of applying iodine? A. To fix the bacteria to the slide B. To act as a mordant C. To decolorize the cells D. To counte rstain the cells Answer: B. To act as a mordant Rationale: Iodine is used as a mordant in Gram staining to enhance the binding of the primary stain (crystal violet) to the cell walls of Gram -
positive bacteria. 3. In microscopy, what is the function of the oil immersion lens? A. To decrease light refraction B. To increase the resolution C. To magnify the image D. To enhance contrast Answer: B. To increase the resolution Rationale: The oil immersion lens is used with a drop of oil to fill the space between the lens and the slide, reducing light refraction and increasing the resolution of the image. 4. What is the primary reason for heat -fixing a bacterial smear before staining? A. To kill the bacteria B. To adhere the bacteria t o the slide C. To enhance the uptake of stain D. To coagulate cytoplasmic proteins Answer: B. To adhere the bacteria to the slide Rationale: Heat -fixing a smear passes it through a flame to adhere the bacteria to the slide, preventing them from being washed off during the staining process. 5. Which of the following is not a step in the Gram staining procedure? A. Application of safranin B. Alcohol decolorization C. Application of crystal violet D. Fluorescence microscopy Answer: D. Fluorescence microscopy Rationale: Fluorescence microscopy is not a part of the Gram staining procedure; it is a different technique used to visualize bacteria that have been stained with fluorescent dyes. 6. What is the purpose of using a counterst ain in differential staining techniques? A. To provide a contrasting color to the primary stain B. To fix the primary stain to the bacterial cell wall C. To increase the magnification D. To differentiate between live and dead cells Answer: A. To provide a contrasting color to the primary stain Rationale: A counterstain is used to provide a contrasting color to the primary stain, allowing for differentiation between cell types or cell structures that do not retain the primary st ain. 7. Which of the following microorganisms would most likely be acid -fast? A. Escherichia coli B. Mycobacterium tuberculosis C. Staphylococcus aureus D. Bacillus subtilis Answer: B. Mycobacterium tuberculosis Rationale: Mycobacterium tuberculosis has a waxy cell wall containing mycolic acid, making it resistant to decolorization by acid -alcohol and therefore acid -fast. 8. In the context of microscopy, what does the term 'resolution' refer to?
positive bacteria. 3. In microscopy, what is the function of the oil immersion lens? A. To decrease light refraction B. To increase the resolution C. To magnify the image D. To enhance contrast Answer: B. To increase the resolution Rationale: The oil immersion lens is used with a drop of oil to fill the space between the lens and the slide, reducing light refraction and increasing the resolution of the image. 4. What is the primary reason for heat -fixing a bacterial smear before staining? A. To kill the bacteria B. To adhere the bacteria t o the slide C. To enhance the uptake of stain D. To coagulate cytoplasmic proteins Answer: B. To adhere the bacteria to the slide Rationale: Heat -fixing a smear passes it through a flame to adhere the bacteria to the slide, preventing them from being washed off during the staining process. 5. Which of the following is not a step in the Gram staining procedure? A. Application of safranin B. Alcohol decolorization C. Application of crystal violet D. Fluorescence microscopy Answer: D. Fluorescence microscopy Rationale: Fluorescence microscopy is not a part of the Gram staining procedure; it is a different technique used to visualize bacteria that have been stained with fluorescent dyes. 6. What is the purpose of using a counterst ain in differential staining techniques? A. To provide a contrasting color to the primary stain B. To fix the primary stain to the bacterial cell wall C. To increase the magnification D. To differentiate between live and dead cells Answer: A. To provide a contrasting color to the primary stain Rationale: A counterstain is used to provide a contrasting color to the primary stain, allowing for differentiation between cell types or cell structures that do not retain the primary st ain. 7. Which of the following microorganisms would most likely be acid -fast? A. Escherichia coli B. Mycobacterium tuberculosis C. Staphylococcus aureus D. Bacillus subtilis Answer: B. Mycobacterium tuberculosis Rationale: Mycobacterium tuberculosis has a waxy cell wall containing mycolic acid, making it resistant to decolorization by acid -alcohol and therefore acid -fast. 8. In the context of microscopy, what does the term 'resolution' refer to?
