Lecture 2

Question 1

What are four terms for defining the optimal growth temperature of a microorganism?

Answer 1

Psychrotroph, psychrophile, mesophile, thermophile Also: I would make sure you know the general temperatures that define each category! Given an environment (ie. a lake, intestinal tract of a mammal, etc) you should be able to predict which types of organisms would predominate.

Question 2

What are three terms to describe the optimal pH for growth of a microorganism?

Answer 2

Neutrophile, acidophile, alkaliophile. Also: which ones do we typically find in food environments and why?

Question 3

Three terms to describe a microbes preference for oxygen?

Answer 3

Strict aerobe, strict anaerobe, facultative anaerobe. Also: what does it mean to be a facultative anaerobe?

Question 4

How does the cell envelope (the outer walls and membrane of bacteria) compare between gram positive and gram negative bacteria?

Answer 4

Revisit slide 16 from lecture 2. I’m not expecting you to know the specific sugars/amino acids making up the peptidoglycan layer (top right of this slide), but you should appreciate that it is very porous; I described it as “chicken wire” in lecture

Question 5

Which part of the cell envelope is the most impermeable?

Answer 5

The inner membrane (also known as the cytoplasmic membrane)

Question 6

Can you describe how a hypotonic and hypertonic solution affects bacterial cells?

Answer 6

See slide 17 from lecture 2. I will also put a better description on the website soon, and will send a note when it is there!

Question 7

What are the branches of the “tree of life?”

Answer 7

See slide 6. Hint- there are three

Question 8

What is the difference between mold and yeast?

Answer 8

Mold have hyphae, yeast tend to be cocci in shape and do not have hyphae

Question 9

What are the 3 broad categories of microbes associated with Food?

Answer 9

See slide 7.

Question 10

In what state are microbes most commonly found in the air? Why?

Answer 10

Spores. The air doesn’t contain sufficient moisture or substrates to allow most bacteria to live in a vegetative state.

Question 11

Why does a bacterial population stop growing during stationary phase?

Answer 11

The bacteria reach their carrying capacity (a number that once reached causes the bacterial population to stop growing) and lack of substrates.

Question 12

What phase are bacteria most commonly found in?

Answer 12

Stationary phase. Many bacteria can persist in stationary phase for a long period of time.

Question 13

Describe the air requirements for the microbes in each test tube tube in the link. Disregard 4 and 5

http://upload.wikimedia.org/wikipedia/commons/9/90/Anaerobic.png

Answer 13

1. Aerobic 2. Anaerobic 3. Facultative anaerobe