Home > MCAT > Quizzes > MCAT Biology Passage 6: Viruses and Prokaryotes
MCAT Biology Passage 6: Viruses and Prokaryotes
Fast practice, instant feedback. Timer auto-submits when time’s up.
Avg score: 74% Most missed: “What would be the effect if someone stepped away and permitted the crystal viole…”
The Gram stain is the most common bacteriologic stain used in the clinical laboratory. It consists of the application of a crystal violet solution to a heat-fixed bacterial smear on a glass slide for 60 seconds. The slide is then rinsed gently in distilled water, and an iodine solution is added for 30 seconds. The slide is again rinsed, and a solution of primarily ethanol is rinsed over the slide for 10–15 seconds. The slide is again rinsed, and a solution of safranin is added for one additional minute. After the slide is rinsed a final time and dried, it is then observed with a microscope at... Show more
MCAT Biology Passage 6: Viruses and Prokaryotes
Time left 00:00
5 Questions

1. What would be the effect if someone skipped the third step with the ethanol solution?
2. What would be the effect if someone stepped away and permitted the crystal violet stain to remain in contact with the cells for 5 minutes?
3. What would be the effect if someone skipped the second step with the iodine solution?
4. What would be the effect if someone skipped the heat fixation process?
5. What category of cells would appear blue after this process?