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Diversity & Classification Exercises

1. How many domains of life are there? What are they?

2. How do archaea differ from bacteria?

3. Match the outermost layer with the organism:


Gram-positive bacterium

Gram-negative bacterium





Outer Membrane

4. How does the chemical make-up of the cytoplasmic and outer membranes differ?

5. What is the region between the cytoplasmic and outer membranes called?

Diversity & Classification Answers

1. There are three domains of life: bacteria, archaea, and eukaryotes.

2. Archaea differ from bacteria in two major ways: (1) archaea do not contain peptidoglycan, the building block of bacterial cell walls, and (2) the proteins in archaea that perform certain vital cell processes, such as transcription and translation, are more similar to the proteins eukaryotes use than the ones bacteria use.

3. Gram positive – Peptidoglycan, Gram negative – Outer membrane, Archaea – S-layer

4. Both membranes are made of lipid bilayers, however, both layers of the cytoplasmic membrane are made of phospholipids. The inner layer of the outer membrane is also comprised of phospholipids, but the outer layer is made of LPS.

5. The periplasm.

Germ Theory Exercises

1. Who was the first person to see single-celled organisms?

2. What did Pasteur’s flasks rule out that sealed flasks could not?

3. Why wasn’t the fact that John Snow saw bacteria in contaminated well water enough to show that cholera was a bacterial infection?

4. What is the third of Koch’s postulates?

5. You are preparing to streak some bacteria on a petri dish. Which of these things need to be sterile?
(A) The petri dish
(B) The growth medium
(C) The stick
(D) A & B
(D) A, B & C

Germ Theory Answers

1. Anton von Leeuwenhoek.

2. Pasteur’s swan-necked flasks gave the broth access to air and any "life force" present in it, while blocking access to dust and microbes. Sealed flasks blocked access to air and so critics argued that the broth was, essentially, smothered by its lack of access to life force.

3. We hate to say it, but ALL well water contains bacteria. Bacteria, they’re everywhere. It’s critical to identify a specific, different bacterial strain in a contaminated population.

4. The third postulate says that you must be to cause a healthy animal to become sick by inoculating it with a pure sample of the infectious agent.

5. The correct answer is E. Using a non-sterile petri dish, growth medium, or stick would lead to contamination of the final culture.

Adaptations to Different Environments Exercises

1. Would you expect an organism that grows at very low temperatures to have a higher A/T or higher G/C content?

2. What are pili made of?

3. What is EPS made of?

4. Name one disease that is caused by bacteria in a spore form.

5. Spores are essentially fortresses of DNA and stored food. True or false?

Adaptations to Different Environments Answers

1. The answer is high A/T. Thermophiles have high G/C content in their DNA to help it stick together. Organisms that grow at very low temperatures have higher A/T content.

2. Pili are made up of units of a protein called pilin.

3. EPS, which stands for extracellular polymeric substance or exopolysaccharide, is principally made up of polysaccharide.

4. Both anthrax and tetanus are caused by spores. Either answer is correct.

5. False. Unlike seeds, spores are unicellular and store very little food.

Bacteria Do Things, Too Exercises

1. What is commensalism?

2. Where does the nitrogen fixed in nitrogen come from and what is it made into?

3. What bacteria are commonly studied in nitrogen fixation research?

4. What are the names of the plant parts where nitrogen-fixing bacteria live?

5. Bacteria in the cow rumen secrete cellulases to digest plant cells. True or false?

Bacteria Do Things, Too Answers

1. Commensalism is the symbiotic behavior in which one species benefits while the other is unaffected.

2. Nitrogen-fixing bacteria convert nitrogen in the atmosphere (N2) into ammonia (NH3).

3. Rhizobium.

4. Root nodules.

5. True.

Diseases Exercises

1. Exotoxins can lead to septic shock. True or false?

2. Not all Vibrio cholerae strains are virulent. True or false?

3. Name two Vibrio cholerae virulence factors.

4. What is the vector for Lyme disease? What organisms serve as its reservoir?

5. Match the bacteria with the disease they cause:
Bacterium Disease
Helicobacter pyloriLyme disease
Vibrio choleraeSyphilis
Treponema pallidumStomach ulcers
Borrellia burgdorferi Legionnaire’s disease
Legionella pneumophilaCholera

Diseases Answers

1. False. Endotoxins released by lysed cells can lead to septic shock.

2. True. Less than 1% of Vibrio cholerae strains (by serotype) are virulent.

3. Cholera toxin (an exotoxin) and the TCP (toxin co-regulated pilus) are both necessary for Vibrio cholerae virulence.

4. Deerticks are the vector and deer are the reservoir for Borrellia burgdorferi, the bacteria that cause Lyme disease.

Helicobacter pyloriStomach ulcers
Vibrio choleraeCholera
Treponema pallidumSyphilis
Borrellia burgdorferiLyme disease
Legionella pneumophilaLegionnaire’s disease

Sterilization Exercises

1. Vibrio cholerae, which causes cholera, is an opportunistic pathogen. True or false?

2. How does an autoclave work?

3. Match the following chemicals with their property.

Rubbing alcohol Disinfectant


4. List up to four ways that antibiotics work.

5. Which of these antibiotics kills bacteria (bacteriostatic, bactericidal)? Why are antibiotics that don’t kill bacteria also effective?

Sterilization Answers

1. False. Vibrio cholerae is a regular pathogen.

2. An autoclave sterilizes equipment by exposing it to hot, high pressure steam. It’s basically a pressure cooker.


Rubbing alcohol Antiseptic


4. Antibiotics work against (1) cell wall synthesis, (2) membrane stability, (3) protein synthesis, (4) DNA and RNA synthesis.

5. Bactericidal antibiotics kill bacteria. Bacteriostatic antibiotics indirectly kill bacteria by freezing their activities. Our immune systems then finish the bacteria off.

Cloning Exercises

1. All bacterial polymerases are thermostable. True or false?

2. What do restriction enzymes do?

3. Why do bacteria methylate their DNA?

4. What does ligate mean?

Cloning Answers

1. False. Only thermophilic prokaryotes have thermostable polymerases.

2. Restriction enzymes cut or digest DNA. (Cutting and digesting DNA mean the same thing.)

3. Bacteria methylate genomic DNA in order to protect it from their own restriction enzymes. Restriction enzymes will then preferentially cut new DNA they encounter, notable bacteriophage DNA.

4. Ligate means to stick or glue together. It usually refers to attaching two double-stranded DNAs to each other.

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