MICROBIOLOGY PORTAGE LEARNING MODULE 3 PRACTICE EXAM QUESTIONS COMPLETE WITH 100% VERIFIED ANSWERS AND DETAILED RATIONALE

MICROBIOLOGY PORTAGE LEARNING MODULE 3 PRACTICE EXAM QUESTIONS COMPLETE WITH 100% VERIFIED ANSWERS AND DETAILED RATIONALE 1. What is the primary structural difference between gram-negative and gram-positive bacteria that affects their staining properties? A) Gram-negative bacteria have a thicker peptidoglycan layer B) Gram-negative bacteria have a relatively thin peptidoglycan layer followed by an outer membrane composed of lipopolysaccharides (LPS) C) Gram-negative bacteria lack a cell wall entirely D) Gram-negative bacteria have a cytoplasmic membrane but no outer membrane Correct Answer: B – Gram-negative bacteria possess a thin peptidoglycan layer with an outer membrane containing LPS, which is the key structural feature affecting their staining characteristics. ________________________________________ 2. During the Gram staining procedure, what happens to gram-negative bacteria when the decolorization wash is applied? A) They retain the crystal violet dye permanently B) They become darker and more visible C) They initially retain the crystal violet dye but lose it during the alcohol wash D) They turn green due to the alcohol reaction Correct Answer: C – Gram-negative bacteria initially trap the crystal violet, but the alcohol decolorization wash disrupts their outer membrane and thin peptidoglycan, causing them to lose the dye. ________________________________________ 3. Which dye is added after the decolorization step specifically to visualize gram-negative bacteria? A) Methylene blue B) Crystal violet C) Safranin D) Malachite green Correct Answer: C – Safranin is a positively charged counterstain applied after decolorization to color gram-negative bacteria that have lost the crystal violet. ________________________________________ 4. By counterstaining with positively charged safranin, gram-negative bacteria appear which color? A) Purple B) Pink C) Blue D) Colorless Correct Answer: B – Safranin imparts a pink/red color to gram-negative bacteria, making them distinguishable from purple gram-positive cells. ________________________________________ 5. What is the generalized term for any staining technique that separates specimens into further subgroups and most often utilizes at least two dyes? A) Simple stain B) Differential stain C) Acid-fast stain D) Negative stain Correct Answer: B – A differential stain uses multiple dyes to categorize bacteria into distinct groups, unlike simple stains which only color all cells uniformly. ________________________________________ 6. Why is it necessary to have tightly adherent cells when performing a staining procedure? A) To allow the cells to move freely B) To prevent sample loss during the staining and wash steps C) To enhance the color of the dye D) To kill the cells more effectively Correct Answer: B – If cells are not tightly adhered to the slide, the rinsing and washing steps will wash them away, leading to sample loss. ________________________________________ 7. What is the most common method used to fix a bacterial sample to a slide? A) Chemical fixation with ethanol B) Air drying C) Heat fixation D) Cryofixation Correct Answer: C – Heat fixation is the most widely used method to adhere microorganisms to a glass slide for staining. ________________________________________ 8. Which fixation method includes the use of paraformaldehyde, ethanol, or methanol? A) Heat fixation B) Chemical fixation C) Ultraviolet fixation D) Flame fixation Correct Answer: B – Chemical fixation employs reagents like paraformaldehyde, ethanol, or methanol to preserve and adhere cells. ________________________________________ 9. What characteristic of microorganisms is lost when chemical fixation is used? A) Cell shape B) Cell size C) Motility (movement) D) Gram reactivity Correct Answer: C – Chemical fixation kills the microorganisms, thereby eliminating any characteristics related to motility. ________________________________________ 10. Which preparation method involves adding a small liquid culture to a slide and covering it with a glass coverslip without performing heat fixation? A) Smear preparation B) Heat-fixed smear C) Wet mount D) Chemical smear Correct Answer: C – A wet mount is a live preparation where the liquid