Gram Staining CONCLUSIONS 1. Ofthese three bacteria, which organisn is the lange
ID: 146159 • Letter: G
Question
Gram Staining CONCLUSIONS 1. Ofthese three bacteria, which organisn is the langest? 2. Did your results agree with the information in your text? If not, why not? QUESTIONS I. Why do gram-positive cells more than 24 hours old stain gram-negative? 2. Can iodine be added before the primary stain in a Gram stain? 3. List the steps of the ram-staining procedure in order (omit washings), and fill in the color of gram-positive Step Chemmical Appearance Gram-Negative Cells 4. Which step can you omit without affecting determination of the Gram reaction? CRITICAL THINKING 1. Suppose you performed a Gram stain on a sample from a pure culture of bacteria and observed a field of red and purple cocci. Adjacent cells were not always the same color. What would you conclude? 2. Suppose you are viewing a Gram-stained field of red rods and purple cocci through the microscope. What do you conclude?Explanation / Answer
2.The gram positive cells more than 24 hours old stain gram negative. Because, the cell wall of the gram positive is vey thick and made up of peptidoglycon. which absorbs the purple colour stain and the gram negative bacteria has thin cell wall so they dont absorb purple colour they take pink colour. Based on the thickness of the cell wall, the cell wall of the positve stain get degenerate after 24 hours. so the gram positve cells more than 24 hours old stain gram negative.
3. The iodine stain should not be added before a primary stain in a gram stain because the iodine will form the complex with the primary stain and allow the crystal violet colour stain to bind with the peptidoglycon i.e the cell wall. so, the primary stain should be added first and followed by the iodine stain.
4. Steps involved in procedure of gram staining.
Four steps are involved in preparing the gram staining (except washing in the tap water)
1. The slide is treated with crystal violet for 1 minute - the cell wall (peptidoglycon) of both positve and negative bacteria will be stained with the crystal violet.
2. Then the slide is treatede with iodine for 1 min - in gram postive the crystal violet and the iodine will form a complex within the cell wall. whereas in the gram negative the crystal violet and the iodine complex is formed but the complex will not get contact with the cell wall.
3. Then the slide is treated with ethanol or acetone for decolourizing - when the alcohol is added the crystal violet colour will not be washed out form the cell wall in the gram positive but in the gram negative the crystal violet colour will be washed out form the cell wall.
4. Finally the slide is treated with safranin - in gram positive already there is a crystal violet stain so there will be no effect for the safranin in the gram postive. But, in the gram negative the violet colour is washed out so here the gram negative will take up the safranin stain.
* Hence the Gram postive stain is in violet or purple in colour and the Gram negative is in red safranin or pink in colour.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.