Biology 156: Lab Practical 3 Test Questions Graded A+

2 domains that contain prokaryotes - Answer-Bacteria and Archaea 2 benefits of bacteria - Answer-1. some bacteria are decomposers, which break down organic material (e.g. sewage treatment), 2. many bacteria in the human body help facilitate functions which aid in digestion Human diseases caused by bacteria - Answer-pneumonia, tuberculosis, gonorrhea, syphilis, chlamydia, cholera, tetnus, botulism, bubonic plague, lyme disease What is the purpose of fixing the smear? - Answer-The purpose of fixing a smear is to make cells stick to the slide, kill bacteria in the smear, and allow for optimal capability for retaining any stains performed 2 methods of fixing the smear - Answer-heat fixation and chemical fixation Heat fixation - Answer-kills the cells, destroying autolytic enzymes, and causes the cells to adhere to the slide chemical fixation - Answer-In microscopy, a technique that uses methyl alcohol or formalin to attach a smear to a slide. advantage of viewing an unstained specimen - Answer-advantage of viewing an unstained specimen is that it doesn't require heat fixation, allowing it to be viewed in its original unaltered form. This is important because some cells are too delicate to undergo the heat from heat-fixation. by only staining the background and leaving the bacteria unstained (i.e. negative staining), the cell's shape and size is preserved and observed 3 stains used in simple staining procedures - Answer-methylene blue, gram safranin, gram crystal violet when are negative stains used - Answer-on cells that are too difficult (e.g. spirilla) or too delicate to undergo the heat from heat-fixation. by only staining background and leaving the bacteria unstained, the cell's true morphological shape, size,and arrangement can be accurately observed and recorded, without altering (shrinking or swelling the cell)how many stains are used in differential staining procedures - Answer-2 stains are used in differential stains (as opposed to just one stain). each stain has a different name first tain is primary stain, second is called countertain. common example of differential staining is the gram stain. acid fast stain is also an example of differential staining. Why is alcohol important during the gram-staining technique? - Answer-without alcohol, the gramnegative bacterium will remain purple because the outer lipopolysaccharide layer will retain its structural integrity (i.e. not be broken down by the acid from the alcohol) gram positive - Answer-stains purple gram negative - Answer-pink