BIO 203 - EXAM II EXAM QUESTIONS

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BIO 203 - EXAM II EXAM QUESTIONS

Actual Qs and Ans Expert-Verified Explanation

This Exam contains:

-Guarantee passing score -23 Questions and Answers -format set of multiple-choice -Expert-Verified Explanation Question 1: Would removing colistin and nalidixic acid from CNA alter the medium's sensitivity or specificity?

Answer:

It would alter specificity because organisms that "shouldn't" grow on it would. It wouldn't likely alter sensitivity because you would probably still be able to detect growth of organisms that "should" grow on it.

Question 2: EMB agar a defined or undefined medium?

Answer:

Undefined due to the gelatin in the medium.Question 3: Is the D value of either organism affected by the size of the population? Explain.

Answer:

It shouldn't be D value represents the time it takes to produce 90% reduction in the population size regardless of the starting size.Question 4: The purpose of this exercise is to demonstrate the comparative effect of UV on two bacterial populations. This could have been accomplished without the cardboard cover. Why was the cover used?

Answer:

UV radiation does not penetrate well. The cover is used as a control to illustrate the amount of growth in

the absence of UV exposure.

Question 5: Role of lactose in EMB agar?

Answer:

ferment lactose to acid end products; lactose is the substrate of the fermentation. Coliforms perform this fermentation, whereas noncoliforms do not.

Question 6: Nitrogen?

Answer:

Organic nitrogen is generally found in proteins and nucleic acids. Gelatin is derived from the protein collagen is the sole source of nitrogen.Question 7: In what ways could you adjust incubation temperature to grow an organism at less than its optimal growth rate?

Answer:

Incubation at any temperature less than or greater than its optimum would produce less than optimum growth rate.

Question 8: What is the purpose of EMB agar?

Answer:

EMB agar is used to isolate gram negatives from clinical samples and to subsequently differentiate between lactose fermenting coliforms and lactose non-fermenting non coliforms.Question 9: In your own words, what ar the roles of colistin and nalidixic acid in CNA and how does each work?

Answer:

Both are antibiotics that affect gram - negative cells. Colistin disrupts membrane integrity and nalidixic acid affects DNA replication.Question 10: Compare the recipes of nutrient agar and Columbia CNA agar. If an organism can grow on both media, on which would you expect it to grow better?

Answer:

Columbia CNA agar is much more nutritious than nutrient agar. Both have the same amount of beef extract, so there is no difference there. The only additional nutrient source in NA is peptone, but Columbia CNA agar has casein, animal tissue, yeast extract, and corn starch. Columbia CNA agar inhibits Gram - negative organisms, but those that aren't inhibited are treated to a diverse menu!

Question 11: Is Columbia CNA agar defined or undefined medium. Provide the reasoning behind your choice and explain why this formulation is desirable.

Answer:

It is undefined due to the casein, animal tissue, yeast extract, beef extract, and corn starch in the medium. the exact compositions of casein and corn starch are unknown and the animal tissue, yeast extract, and beef extract contain the array of biochemicals found int he cells of each. Any of those would make the medium undefined.The goal of this medium is to isolate desired organisms, and once the undesired organisms have been inhibited you want the desired ones to grow well. The variety of biochemicals in animal tissue, yeast extract, and beef extract make the medium more likely to satisfy the varied nutritional needs of the organisms being selected for.

Question 12: EMB ingredients

Carbon?

Answer:

Gelatin and lactose contain usable carbon.Question 13: This is not a quantitative exercise. Keeping this in mind, can you see a general trend between bacterial death and UV exposure time?

Answer:

Longer exposure results in a higher percentage of cells killed.

Question 14: Role of eosin Y and methylene blue in EMB agar?

Answer:

Both as selective agents against Gram positives. They also are responsible for the color changes produced by lactose fermenters.

Question 15: Which organism survived the longest exposure? Why?

Answer:

• subtilis survived the longest because of the presence of spores.

Question 16: What is the application (purpose) of Columbia CNA with 5% sheep blood agar?

Answer:

Columbia CNA agar is selective and differential medium. It inhibits the growth of gram negatives and allows isolation of gram positives. Hemolytic gram positives, such as staphylococcus, streptococcus, or enterococcus species can frequently be differentiated from other Gram positives because of their hemolytic reactions.

Question 17: Why do different temperatures produce different growth rates?

Answer:

Enzymes have different shapes at different temperatures. The optimum temperature results in the best fit between enzyme and its substrate. Other temperatures produce less than an optimal fit between the enzyme and substrate resulting in a slower reaction rate and in turn, a slower growth rate.Question 18: Why might colistin affect gram - negative bacteria more severely than gram - positive bacteria?

Answer:

Colistin affects the membrane, which invariably interferes with an organism's ability to maintain osmotic homeostasis. With its thicker peptidoglycan wall, Gram - positive cells are more likely to delay lysis when the membrane fails.

Question 19: What is the role of sheep blood in CNA agar?

Answer:

Sheep blood supplies iron containing heme. Iron is essential element for growth. In addition, inclusion of sheeep blood makes this a differential medium based on the degree of hemolysis each organism produces.Question 20: What ingredient(s) in Columbia CNA with 5% sheep blood agar supply(ies) Carbon?

Answer:

Casein (milk protein), animal tissue, yeast extract, beef extract, and corn starch can supply carbon in a variety of forms.Question 21: Why is it not advisable to connect the data points to each organism in your graph?

Answer:

The gaps between temperatures used in this experiment are large. Since there is a variable correlation between temperature and growth rate, we can't be certain of what the graph looks like between those five data points. We would be making more out of our data than our data reasonably allows.Question 22: Why were you told to remove the plate covers prior to exposing them to UV?

Answer:

UV doesn't penetrate well and if the plate lids had been left on, the organisms would have not bee exposed to much UV radiation.