Lab exam Chapter 3 BIOD 171learning portage

Lab exam Chapter 3 Exam Page 1 Answer the following questions. 1. List the 4 main steps used to prepare a DRY mount and indicate which step is optional. 1. Clean slide( 70% ethanol) 2. Circle area on slide for easy location of specimen (OPTIONAL) 3. Apply organism to slide - If from culture, use sterile loop to spread onto the slide - If from plate; use sterile loop to pick colonies and mix with a drop of sistilled water 4. Air dry at room temp until all moisture has evaporated 2. Why is it important to first clean your slide before applying your sample? Its important to throughly clean slide to risk comtaminatiing the slide the next time its being used. Part of the sample you use on the slide could mix with the sample use on the next slide and ruin it 3. When performing a wet mount technique, what is the advantage of using a wax or hydrophobic pen? Wax or hydrophobic pen are used to seal the sample along with coverslip, as it can prevent the water loss from slide. It also hold the coverslip in place for longer periods 4. What dye do Gram-positive bacteria primarily retain? Crystal violet Answer Key Answer the following questions. 1. List the 4 main steps used to prepare a DRY mount and indicate which step is optional. 1 – Clean slide 2 – Circle area on slide for specimen placement (OPTIONAL) 3 – Apply organism to slide 4 – Air dry at room temperature This study source was downloaded by from CourseH on :39:39 GMT -05:00 2. Why is it important to first clean your slide before applying your sample? You must first remove any unwanted contaminants from the slide otherwise it may be difficult to distinguish between the pathogen of interest and a contaminant. 3. When performing a wet mount technique, what is the advantage of using a wax or hydrophobic pen? Creating a hydrophobic barrier (the circle) helps to keep the water within the circle so it does not spill off of the slide. 4. What dye do Gram-positive bacteria primarily retain? Crystal violet Exam Page 2 Answer the following questions. 1. Why do Gram-negative bacteria stain red? It stain red due to the thinner pepidolglycan layer in their cell wall 2. Identify the stain and shape of the bacteria pictured below. Gram postive : cocci (Spherical) This study source was downloaded by from CourseH on :39:39 GMT -05:00 3. When might you want to utilize a negative stain technique in the lab? What is the name of the primary dye used in this technique? You many utilize negative stain technique when the stain cell are too delicate to be heat fixed. Nigrosin( acidic dye) is usually used 4. Why do bacteria repel the dye nigrosin? Nigrosin is a negatively charged dye. The membrances of most cells are also negatively charged. The membrance will repel the dye not allowing it to absorbed Answer Key Answer the following questions. 1. Why do Gram-negative bacteria stain red? Gram-negative bacteria have a thin peptidoglycan layer in their cell wall. During the alcohol rinse step, the cell wall cannot retain the crystal violet dye. It will be washed away. The cell wall will then absorb the counter stain, safranin. 2. Identify the stain and shape of the bacteria pictured below. Gram-positive; Cocci (spherical) This study source was downloaded by from CourseH on :39:39 GMT -05:00 3. When might you want to utilize a negative stain technique in the lab? What is the name of the primary dye used in this technique? A negative stain is used to identify organisms with an opaque structure. Nigrosin dye. 4. Why do bacteria repel the dye nigrosin? Nigrosin is a negatively charged dye. The membranes of most cells are also negatively charged. The membrane will repel the dye not allowing it to be absorbed. Exam Page 3 Answer the following questions. 1. What is one disadvantage of heat fixing a sample? It kills the specimen. Inability to determine motility, distoration of cell size and shape. 2. What is the proper way to dispose of all materials used during the lab? All materials must be place in a biohazardous waste bag and plced into an auto clave for sterilization 3. What are the Gram status, shape and identification of organism #2 from the Gram stain procedure? Gram negative. Bacillus rod Ecoli 4. What are the Gram status, shape and identification of organism #5 from the Gram stain procedure? Gram postive . Cocci sperial. Streptoccus Answer Key Answer the following questions. This study source was downloaded by from CourseH on :39:39 GMT -05:00 1. What is one disadvantage of heat fixing a sample? The heat fixing procedure kills the specimen. This also prevents any observations on motility and enzymatic properties. 2. What is the proper way to dispose of all materials used during the lab? All materials must be place in a biohazardous waste bag and placed into an autoclave for sterilization. 3. What are the Gram status, shape and identification of organism #2 from the Gram stain procedure? Gram-negative; Bacillus (rod); E. Coli 4. What are the Gram status, shape and identification of organism #5 from the Gram stain procedure? Gram-positive; Cocci (spherical) chain; Streptococcus