Microbiology Lab Test, Micro lab 1 Exam Questions and Answers

Microbiology Lab Test, Micro lab 1 Exam Questions and Answers Why are thick or dense smears less likely to provide a good smear preparation for microscopic evaluation? -Answer-It will diminish the amount o flight that can pass through making it difficult to see under the microscope. Why is it essential that smears be air-dried? Why can't they be gently heated over the flame to speed up the drying process? -Answer-1. Overheat will denature and rupture the cell wall. 2. excess water on the slides will boil during fixation Why should you be careful not to overheat the smear during the heat-fixing process? - Answer-Overheating will distort the morphology through plasmolysis of the cell wall Why do you think the presence of grease or dirt on a glass slide will result in a poor smear preparations? -Answer-1. Bacteria will attach to the grease or dirt and wash away when staining. 2. It can also diminish the microscopic light making it hard to see the cells. Why are basic dyes more effective for bacterial staining than acidic dyes? -Answer- Basic stains with a positively charge chromogen are preferred because bacterial nucleic acid and certain cell wall components carry a negative charge that strongly attract and binds to the cationic chromogen. Can simple staining technique be used to identify more than the morphological characteristics of microorganisms? Explain -Answer-Yes, the purpose of simple staining is to elucidate the morphology and also arrangement of bacteria cells. During the performance of the simple staining procedure, you failed to heat fix your E. coli smear preparation. Upon microscopic examination, how would you expect this slide to differ from the correctly prepared slides? -Answer-When heat fixing the bacteria, the bacterial proteins are coagulated and fixed to the glass surface. If fail to heat fix, the bacteria will wash away when staining. During a coffee break, your friend spills coffee on your lab coat and the fabric is discovered. Is this a true biological stain or simply a compound capable of imparting color? Explain your rationale. -Answer-Coffee does not contain an auxochrome group which conveys the property of ionization to the chromogen, enabling it to form salts and bind to fibers or tissues. What are the advantages of differential staining procedure over the simple staining techniques? -Answer-The differential staining determine the shape, arrangement, and gram reaction while the simple staining only determine the morphology Cite the purpose of each following reagents in the differential staining procedure: Primary stain, counterstain, decolorizing agent, mordant. -Answer-Primary stain: to impart its color to all cells Counterstain: Determine gram-positive (retain the purple primary color) or gram- negative (undergo decolorization). Decolorizing agent: remove excess dye of cell and may or may not remove the primary stain from entire cell or only certain cell structure Mordant: Increases the cells' affinity for a stain Why is it essential that the primary stain and the counterstain be of contrasting color? - Answer-So it can be distinguished from each other