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Biology 11 - Part C Forero
BACTERIA - Gram Stain Virtual Lab
Bacillus anthrasis
Treponema pallidum
Escherichia coli
Observations of Gram Stained Bacteria
Gram + or +
1. How is the cell wall different from the plasma membrane?
The cell wall is the outermost boundary in plant, bacteria and some fungal cells.
The plasma membrane or cell membrane is the outermost boundary in animal
cells and the inner membrane in plant, bacteria and some fungal cells.
- cell membrane is present in all cells
- cell wall is absent in animal cells
- cellulose in plant cell wall
- peptidoglycan in bacteria cell wall
- chitin in fungal cells wall
2. In what way(s) is the cell wall different between Gram positive and Gram negative
Gram-positive bacteria retain crystal violet dye and stain dark violet or purple.
They remain coloured purple when washed with absolute alcohol and water
because of their thick (multilayered) peptidoglycan layer in their cell wall.
Gram- negative bacteria don't retain the crystal violet stain when washed with
absolute alcohol and acetone because of their thin (single-layered)
peptidoglycan layer in their cell wall, which gets degraded when washed with
alcohol and water. They can accept the counter stain (Safranin or Fuchsine) to
stain red or pink because this now porous peptidoglycan layer is sandwiched
between an inner cell membrane and a more complex outer cell wall.
3. In what type(s) of organisms would the Gram stain not work? Why?
- organisms that DON’T have a cell wall
- Ex: viruses, animal cells, some species of archaea, protists and fungi
4. How is the Gram stain reaction by bacteria useful information to medical doctors or
Bacteria can be classified into two groups based on the structure of their cell wall.
These to groups can be identified through Gram staining. Not all of the organisms
of either group are harmful, but it is helpful to narrow down what cell wall
structure the bacteria you are dealing with has in order to choose the appropriate
antibiotic to treat it if it is harmful. This can be useful in the food industry and