Answer all the following questions (50) on scantron card. Choose the one alterna

Question

Answer all the following questions (50) on scantron card. Choose the one alternative that best completes the statement or answers the question. Please return scantron cards and question sheet. Time allowed: 1 hour 1.Aloop or needle is sterilized by inserting it to a Bunsen bumer until it is red hot. This will a, coagulate any contaminating organisms that may be present b. incinerate any contaminating organisms that may be present c. activate any contaminating organisms that may be present d, all of the choices are true 2. With a pure culture, one is able to study a. the cultural characteristics of an individual organism b. the morphological characteristics of an individual organism c. the physiological characteristics of an individual organism d, all of the above 3. The use of a single stain to color a bacterial cell is commonly refemed to as a. special stain b. simple stain c. negative stain d. pure stain 4. The phase contrast microscope is best suited for observing a. living organisms in an uncovered drop on a slide b. stained slides with cover glasses c, living organisms in hanging drop slide preparation d, living organisms on a slide with a cover glass 5. The coarse and fine adjustment knobs adjust the distance between a. the objective and the ocular lenses c. the ocular lenses b. the stage and the objective lens d. the stage and the condenser 6. The resolving power ofa microscope is a function of a. the magnifying power of the lenses b, the numerical aperture of the lenses c. the wavelength of light d, both b and c are correct 7. Anionic chromophores are classified as c. neutral dyes d none of the above a. acidic dyes b. basic dyes 8. Which of the followings is a Gram-negative rod? a. Pseudomonas aeruginosa c Bacillus megaterium b. Staphylococcus aureus d. Moraxella catarrhalis 9. Cocci that are found in pairs are called b. eukaryotes c. staphylococci d. spirochetes a. diplococci

Explanation / Answer

1 b. Inserting a loop or needle into a bunsen burner until it is red hot will incinerate all contaminating organisms on it, thereby sterilizing the loop or needle.

2 d. With a pure culture we can study the cultural, morphological and physiological characteristics of a single organism.

3 b. A simple stain uses a single stain to stain an organism e.g methylene blue or safranin.

4 d. Phase contrast microscopy is used to observe living cells. A small sample is placed on a microscope slide and covered with a cover slip and then viewed under the phase contrast microscope.

5 b. The coarse and fine adjustment knobs are used to adjust the distance between the stage and the objective lens.

6 d. The resolving power of a microscope depends on the wavelength of light and the numerical aperture of the lenses.

7 a. Anionic chromophores are acidic negatively charged dyes, e.g acid fuchsin, Congo red, nigrosin.

8 a. Pseudomonas aeruginosa is a Gram negative rod. Bacillus is a Gram positive rod, Staphylococcus are Gram positive cocci. Moraxella are Gram negative coccobacilli.

9 a. Diplococci are cocci found in pairs, e.g Pneumococcus.

23 c. The pH indicator Phenol red, is yellow at acidic value and red at alkaline pH. It has a pH range of 6.8 to 8.2 where its colour changes gradually from yellow to red. Above pH 8.2 it changes colour to a bright pink.

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