Micro lab post 11,12,13 PDF

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Casie Harkins L7 2/24/18 Laboratory Report 11 1. How does smear preparation of cells from a lipid medium differ from preparation of cells from a solid medium? If the bacteria are growing in a liquid medium one starts by placing two or more loopfuls of the liquid medium directly on the slide. From solid media such as nutrient agar, blood agar, or some part of the body, one starts by placing one or two loopfuls of water on the slide and then using an inoculating loop to disperse the organisms in the water. 2. Why is it important to limit the quantity of cells used to prepare a smear? Thickness of the smear will determine if you can visualize individual cells, their arrangement, or details regarding microstructures associated with cells. 3. Describe the potential consequences of making a smear that is too thick. Thick smears with large clumps can obscure details about arrangement and the presence of internal structures. Stain can become entrapped in the clumps of cells, preventing its removal by destaining and washing and leading to erroneous results for staining reactions. 4. For preparation of a smear on a slide, what is the purpose of heat fixation? What problems can arise when the slide is heated in a flame? Heat-fixation fixes organisms to slide. Avoid prolonged heating of the slide as the can result in the slide shattering and injuring you.

Laboratory Report 12 1. What are chromophores? Color-bearing ionic groups. 2. What is the difference between basic and acidic dyes? Basic dyes stain the cells, acidic dyes stain the background of the slide instead. 3. Why do acidic dyes not stain bacterial cells? They are repelled by bacterial cells. 4. Crystal violet is an example of what type of stain? Basic dye 5. What is meant by palisade arrangement of cells? Parallel arrangement of rod-shaped cells.

Laboratory Report 13 1. What type of chromophore is associated with a negative stain? Negatively charged chromophore that doesn’t penetrate the cell but rather is repelled by the similarly charged bacterial cell.

2. What is an example of a negative stain? India ink and nigrosin. 3. What step normally associated with staining bacterial cells is omitted when the dimensions of cells are determined? Why? Heat fixation because no shrinkage of cells occurs, and size determination are more accurate than those determined on fixed material. Avoiding heat fixation is also important if the capsule surrounding the cell is to be observed because heat fixation will severely shrink this structure. 4. What external bacterial cell structures can be demonstrated by a negative stain? Capsules...