Various techniques have been developed to isolate strains of bacteria carrying a particular mutation. One of them is, bacteria containing wild-type cells and cells of a desired mutant are grown on a medium lacking the nutrient for which the desired mutants are auxotrophic but containing an antibiotic that only kills growing cells. In this environment,

Question

A.  both wild-type and mutant cells are killed.
B.  both wild-type and mutant cells survive.
C.  wild-type cells survive; mutant cells die.
D.  wild-type cells die; mutant cells survive.
E.  only double mutants survive.

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
 
Gather Content
· What do you already know about the bacteria? How does it relate to the question?
· What other information is related to the question? Which information is most useful?

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
 
Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

D.  wild-type cells die; mutant cells survive.

Clarify Question
· What is the key concept addressed by the question?
        o The question describes two types of bacteria and the medium they are growing in. You need to determine whether each strain of bacteria will survive.
· What type of thinking is required?
        o This question is an “analyze” question. You need to use your knowledge of bacterial growth to pick the most likely answer.
 
Gather Content
· What do you already know about the bacteria? How does it relate to the question?
        o In this question, you have two strains of bacteria: “wild-type” and a mutant.
            · The wild-type bacteria are the normal strain.
            · The mutant bacteria are auxotrophic for the nutrient zinc. The growth medium does not contain zinc. Will the mutant bacteria thrive or suffer on this type of growth medium?
· What other information is related to the question? Which information is most useful?
        o The growth medium does not contain zinc. Also, it contains an antibiotic that kills growing bacteria. Is there a way bacterial cells could survive this environment?
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Treat this question as a short-answer question. Write down your answer for each of the bacterial strains separately. Now, find the option that gives the correct answer for BOTH strains.
 
Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o This question asked you to determine what would happen to two different bacterial strains grown in the same medium.
        o If you got the correct answer, great job!
        o If you got an incorrect answer, where did you get stuck?
            · This is a very complicated question, and you had to come up with the correct answer for each of the strains. In a question like this, it is best to break it into pieces. For example, focus on just the wild-type strain first. Will it survive or die? Then, focus on just the mutant strain. This makes the question easier.