A researcher places several colonies of Clostridium, an obligate anaerobe, in a nutrient-rich broth but accidentally leaves the caps off the test tubes. Returning the next day, she notices that none of the tubes have shown bacterial growth. Which of the following is the most likely explanation for the lack of growth?
A. Oxygen from the air diffused into the broth and the lack of enzymes capable of breaking down the superoxide anion lead to death by oxygen toxicity.
B. Fungal spores in the air landed in the broth and the subsequent fungal growth consumed the available nutrients.
C. The ambient temperature of the air cooled the broth below the optimal growing temperature of 37ºC, causing the Clostridium to die off.
D. The failure to cap the test tubes was irrelevant and the Clostridium must have died due to some unknown factor.
Click for Explanation
Clostridium is an obligate anaerobe, as the question states. In the presence of atmospheric oxygen, the bacteria will die off. There are number of various factors that create oxygen toxicity, but one of the major ones is the absence of enzymes necessary to deactivate toxic oxygen species. Thus (A) is the correct answer.
B: The question makes no mention of fungal growth, and we have no reason to suspect that fungal spores in the air would be of a species capable of out-competing the bacteria for nutrients.
C: The ambient temperature in the room is unlikely to kill off bacteria. Cooler than optimal growing conditions may slow bacterial growth, but room temperature is unlikely to be fatal.
D: See explanation above for (A).
Want more MCAT practice?
We’ve got options for every schedule and learning style!
From the best online MCAT course created by top instructors with 524+ MCAT scores to the most representative full-length practice exams and private tutoring, we can custom tailor your MCAT prep to your goals!
Not sure which option is right for you? Schedule a free MCAT consultation with an MCAT expert using the form below. No obligation, just expert advice.
Related Post
Search the Blog
Free Consultation
Interested in our Online MCAT Course, One-on-One MCAT Tutoring or Med admissions packages? Set up a free consultation with one of our experienced Senior Student Advisors.
Schedule NowPopular Posts
-
-
-
-
-
MCAT Blog How to Review MCAT Full-Lengths
Free MCAT Practice Account
Need great MCAT practice?Get the most representative MCAT practice possible when you sign up for our free MCAT Account, which includes a half-length diagnostic exam and one of our full-length MCAT practice exams.
Learn More
Submit a Comment