Question

4. After performing a Gram stain on a Gram negative bacteria, the specimen shows purple bacteria. Which of the following best explains why this occurred? A. Crystal violet was not used B. Decolorizer was not used C. The specimen was not heat-fixed D. Safranin was not used

5. Which of the following pieces of evidence could support the endosymbiotic theory if found in some eukaryotes? A. Presence of 80S ribosomes B. The presence of formylated methionine C. Genes that allow for multiple origins of replication D. Gene for expressing reverse transcriptase

6. A animal cell placed into a isotonic environment will: A. Not change noticeably B. Lyse C. Shrivel D. Will “puff up” and swell but not lyse

7. Which of the following correctly demonstrates the streaking method to obtain single colonies? Answer: 5. A researcher wishes to decrease the reactivity of an enzyme. Which of the following can she do? A. Increase temperature B. Add an allosteric activator C. Add an allosteric inhibitor D. Add a competitive activator

8. What kind of oxygen requirement does the culture in the figure MOST likely have? A. Microaerophile B. Facultative anaerobe C. Obligate aerobe D. Obligate anaerobe 7.

10. Which of the following could NOT explain why a streaked plate did not yield single colonies? A. The inoculation loop was flamed before streaking B. The plate was contaminated C. After the first quadrant was inoculated, all following quadrants were streaked from the first quadrant D. The inoculation loop was not flamed after the initial inoculation

11. You have recently identified a new toxin. It is produced by a gram-negative bacterium. It is has a lipid portion, and heat stable. Based on these characteristics, how would you classify this toxin? A. superantigen B. endotoxin C. exotoxin D. A-B toxin

Answer 1

Answer 4 :

Option B - Decolorizer was not used

In gram Stain, The use of decolorizer removes the primary stain from the cells. The culture is gram negative and yet has retained the gram positive color therefore the only explanation will be the decolorizer was not used.

Answer 5 :

Option B - The presence of formylated methionine

In most eukaryotes, mitochondria have N-Terminal methionine excision pathway just like bacteria. Hence, this finding supports the endosymbiotic theory.

Answer 6 :

Option A - Not change noticeably

In an Isotonic solution, the concentration of the solute inside and outside the animal cell is similar. Therefore, there will be no movement of water in or out of the cell and hence there will be no change.  

Answer 7 : Options of Streaking methods are missing. Hence cannot choose the right option.

Answer 5 :

Option A - Increase temperature.  

Enzymes are proteins by nature and each enzyme has its optimum temperature. If the temperature is increased to more than the optimum temperature, the protein will get denatured thereby decreasing the reactivity of an enzyme.

Answer 8 : FIgures missing to analyse and choose the correct option

Answer 10 :

Option A -  The inoculation loop was flamed before streaking

If the inoculation loop was flamed before streaking, it will contribute to formation of single isolated colonies. But the plate does not show such colonies and hence, this cannot be the contributing factor.

Answer 11 :

Option B -  endotoxin

Endotoxins are commonly produced by gram negative bacteria. They are component of bacterial  cell membranes. They have Lipid A, a component responsible for its toxicity.