1. Genes A, B, and C are three structural genes of an operon and fall in that order within the operon. A mutation occurs in Gene A that halts transcription early in the gene. What effect will this have on the levels of proteins produced by Genes A, B, and C? 

a. No proteins coded by genes A, B, and C will be produced.

b. Proteins coded by genes B and C, but not gene A, will be produced 

c. Proteins coded by genes A, B, and C will be produced.

d. Only proteins coded by gene A will be produced.

2. Which of the following is an advantage of the human microbiota?

a. It can aid in food digestion.

b. It can inhibit the growth of pathogenic microbes.

c. It can aid in biosynthesis.

d. It can aid in nutrient absorption.

e. All of these

3. Vibrio cholerae is isolated from a GI sample and testing for cholera toxin is negative. Upon coculture with a bacteriophage, testing for cholera toxin becomes positive. This switch from a nontoxic strain to a toxic strain was mediated by: 

a. Horizontal gene transfer by conjugation

b. Vertical gene transfer

c. Horizontal gene transfer by transduction

d. Horizontal gene transfer by transformation

4. In a prokaryotic operon, genes that code for enzyme proteins are called

a. structural genes.

b. operator genes.

c. repressor genes.

d. inducer genes.

e. regulatory genes.

5. A plasmid 

a. An extrachromosomal piece of DNA that might confer a selective advantage to a microbe.

b. A chromosomal site to which genetic activity can be traced.

c. A molecule that carries the genetic message of the chromosomal DNA.

d. A cytoplasmic structure that transfers an amino acid to mRNA. 

6 Clostridium tetani and Bacillus cereus are both examples of 

a. Gram-negative rods.

b. Normal microflora of the human body.

c. Non-spore forming Gram-positive bacilli.

d. Spore-forming Gram-positive bacilli.

7. Protein toxins that may interfere with host cell function or damage host cell membranes and are usually secreted by living bacteria are called

a. adhesion factors.

b. antibodies.

c. exotoxins

d. endotoxins.

8. Cell walls of Gam negative bacteria contain (select one: thin or thick) layer of peptidoglycan, whereas cells walls of Gram-positive bacteria contain a (select one: thin or thick) layer of peptidoglycan.

Part B. Short Answers 

Answer the questions below as completely and as thoroughly as possible and where appropriate include a specific example to illustrate. Answer the questions in essay form (not as an outline or bullets) using complete sentences. You may use a diagram or table to supplement your answers, but a diagram or table alone without appropriate discussion will not be adequate for full credit. Reminder: All answers are to written in your own words and include complete and accurate citations for the sources you used or that support your answer. No points will be earned for answers that do not include complete and accurate citations for the sources of information used to answer the question or that support your answer. 

9. What is an endospore? Describe its structure and function for a bacterial cell. Name at least two infections transmitted to humans by bacterial endospores and the bacteria (genus and species names) that cause them.

10. List three different mechanisms (be specific about the way they work) by which antibiotics are effective against bacterial infections and give an example of an antibiotic for each of the mechanisms.

11. Explain how a population of antibiotic-resistant bacteria might develop from non-resistant bacteria in response to increased exposure to antibiotics.

Part C. Gram Stain Investigation

12. Gram stain investigation: copy your answers to the Gram stain investigation lab. 

1. What were your results? Name the bacteria and appearance after staining.
2. Describe two ways the food(s) could have become contaminated.
3. Name two ways contamination could have been avoided.
4. Did you find any microorganism known not to cause food poisoning? What? 
5. In what ways does Gram staining aid in the identification of unknown bacteria? 
6. What is a mordant and what is its purpose in the Gram stain procedure? What reagent in the Gram stain procedure functions as a mordant?  
7. If you forgot to add the iodine, would the Gram-positive bacteria still be purple at the end of the staining procedure? Explain why or why not. 

13. Control slides are missing in The Gram Stain Investigation. What are they and what is their importance in the straining procedure? Cite sources of information or sources that support your answer.