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The Gram Stain Trivia Quiz

A very common technique in microbiology is the Gram stain. It is used to separate bacteria into two groups; Gram positive and Gram negative. How much do you know about it?

A multiple-choice quiz by ace_zeke. Estimated time: 4 mins.

Author
ace_zeke

Time
4 mins

Type
Multiple Choice

Quiz #
272,193

Updated
Jan 22 23

# Qns
10

Difficulty
Average

Avg Score
6 / 10

Plays
4886

Last 3 plays: Guest 50 (4/10), 1nn1 (9/10), Guest 24 (7/10).

Question 1 of 10

1. The Gram stain differentiates between bacteria based on the composition of their _________. Hint

Nucleus

Cell Wall

Mitochondria

Cell Membrane

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Question 2 of 10

2. What colour do Gram positive and Gram negative bacteria take; respectively? Hint

Yellow and Orange

Pink and Purple

Purple and Pink

Orange and Yellow

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Question 3 of 10

3. Which of these factors will not affect your Gram stain results? (Given that everything else is done correctly.) Hint

Sample Thickness

Excessive Washing of Slide

Bacterial Age

Reagent Quality

4. Doing a Gram stain from a culture in broth simply requires the use of a few loops of culture. However, if you want to do a stain from a colony on media, what must you add a drop of to the microscope slide beforehand?

Answer: (One Word ... name only; no chemical formula)

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Question 5 of 10

5. Before you use your reagents to stain the bacteria, you need to heat fix your sample first by waving the slide through the blue flame on a Bunsen burner a few times. Why do you do this? Hint

So that the bacteria will perform a musical number for your enjoyment

So that the bacteria will react to the stain

So that the bacteria will not be washed off

So that the bacteria will not die

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Question 6 of 10

6. _______ is the first reagent used in the stain. You have to wait 30 seconds before tipping it off and washing your slide with water. Hint

Neutral Red

Alcohol

Crystal Violet

Iodine

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Question 7 of 10

7. _______ is the second reagent used in the stain. You have to wait 30 seconds before tipping it off and washing your slide with water. Hint

Iodine

Alcohol

Crystal Violet

Neutral Red

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Question 8 of 10

8. _______ is the third reagent used in the stain. Using a squirt bottle, you 'wash' the slide until the liquid coming off changes from purple to clear. Wash your slide with water afterwards. Hint

Neutral Red

Crystal Violet

Alcohol

Iodine

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Question 9 of 10

9. _______ is the fourth, and final, reagent used in the stain. You have to wait 10-30 seconds before tipping it off and washing your slide with water. Pat it dry with some paper towel and you are finished. Hint

Crystal Violet

Neutral Red

Iodine

Alcohol

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Question 10 of 10

10. I've just finished doing a Gram stain, and am packing up my things when I notice a large purple dot on my thumb; what did I forget to do? Hint

Wear protective gloves

Wipe down my counter/bench

Wash my hands (beetroot sandwich for lunch)

Sterilize my thumb

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Quiz Answer Key and Fun Facts

1. The Gram stain differentiates between bacteria based on the composition of their _________.

Answer: Cell Wall

I hope you didn't pick nucleus, as bacteria are prokaryotes.

Gram positive bacteria have a cell wall composed of ~90% peptidoglycan, whereas Gram negative bacteria only have about 10% in their cell wall and so cannot retain the crystal violet after decolourisation with alcohol.

2. What colour do Gram positive and Gram negative bacteria take; respectively?

Answer: Purple and Pink

The purple colour is caused by the crystal violet. This dye is trapped when alcohol and acetone are added, as the cell wall is denatured and retains it.

Gram negative bacteria however, lose the dye when the mixture is added; and so take up the neutral red when it is added.

3. Which of these factors will not affect your Gram stain results? (Given that everything else is done correctly.)

Answer: Excessive Washing of Slide

Excessive washing should only be a problem if you had not heat fixed your slide; in which case you would have problems anyway.

Besides the three options listed earlier (Sample thickness, bacterial age and reagent quality), excessive rinsing with alcohol and overheating the bacteria will also affect your Gram result.

Answer: Water

A drop of water is added so that the colony can be evenly dispersed; if you did not do this, you would most likely have one large clump of bacteria, which you would not be able to look at in the hopes of seeing a structure.

5. Before you use your reagents to stain the bacteria, you need to heat fix your sample first by waving the slide through the blue flame on a Bunsen burner a few times. Why do you do this?

Answer: So that the bacteria will not be washed off

When you wash off the different compounds, your bacteria will simply wash off also if they are not heat fixed to the slide.

6. _______ is the first reagent used in the stain. You have to wait 30 seconds before tipping it off and washing your slide with water.

Answer: Crystal Violet

Once you have washed the crystal violet off, all of the bacterial cells should be purple, as they have taken up the dye.

7. _______ is the second reagent used in the stain. You have to wait 30 seconds before tipping it off and washing your slide with water.

Answer: Iodine

After adding iodine, all cells will still be purple, as they have not yet lost their ability to retain the crystal violet dye.

8. _______ is the third reagent used in the stain. Using a squirt bottle, you 'wash' the slide until the liquid coming off changes from purple to clear. Wash your slide with water afterwards.

Answer: Alcohol

Once you have washed the slide with alcohol, the cells will be decolourised. All Gram negative cells will now be colourless because their cell walls will have ruptured, and so they are unable to retain the dye. However, all Gram positive will still be purple as they are able to retain the dye due to the structure of their cell wall.

Answer: Neutral Red

Once you have added the neutral red, all of the Gram negative bacteria will now be coloured red/pink since they will take up the neutral red. This is done so that we can still view and identify the Gram negative bacteria.

10. I've just finished doing a Gram stain, and am packing up my things when I notice a large purple dot on my thumb; what did I forget to do?

Answer: Wear protective gloves

When you are doing the Gram stain, it is highly recommended that you wear gloves, as crystal violet, iodine and neutral red all stain your skin. Although, a stain will come off within a few hours, or by the next day at the latest.

I actually have a purple dot on my finger and a red line on my palm this very moment; I also forgot to wear gloves during my microbiology practical today.

Thanks for playing, and hope you learnt something.

Source: Author ace_zeke

This quiz was reviewed by FunTrivia editor crisw before going online.
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