객관식
Which stain provides critical information about the peptidoglycan structure of the bacterial cell wall?
146
views
9. Microscopes
Gram Stain
객관식
After Gram's iodine is added during the Gram stain procedure, what color do bacterial cells typically appear under a light microscope?
A
Purple
B
Red
C
Green
D
Colorless
검증된 단계별 안내1
Understand the role of Gram's iodine in the Gram stain procedure: Gram's iodine acts as a mordant, which means it forms a complex with the crystal violet dye previously applied to the bacterial cells.
Recall that after the crystal violet stain and Gram's iodine treatment, the cells are subjected to a decolorization step with alcohol or acetone. However, this step has not yet occurred at the point when Gram's iodine is added.
Recognize that the crystal violet-iodine complex is large and insoluble, so it gets trapped inside the thick peptidoglycan layer of Gram-positive bacteria, causing these cells to retain the purple color.
Note that Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane, so the complex is not retained as strongly, but immediately after Gram's iodine is added (before decolorization), both Gram-positive and Gram-negative cells appear purple.
Therefore, under a light microscope immediately after Gram's iodine is added, bacterial cells typically appear purple because the crystal violet-iodine complex is still present in the cells.
관련 영상
관련 실천
