Three different bacterial strains (P, Q, and R) when grown independently in a culture medium showed typical growth curves. Equal number of cells from all three actively growing cultures are mixed and grown together for 10 days. The number of bacteria (N) are counted each day and plotted. Assuming nutrients are not limiting, the correct explanation for the observed trend is:
Show Hint
A sharp decline followed by a subsequent rapid recovery in population size in the presence of a selective agent (like an antibiotic produced by a competitor) is a classic signature of the evolution of resistance via natural selection.
Q is an antibiotic producer, P is antibiotic sensitive, and R is antibiotic sensitive but evolves resistance during the course of the experiment.
Q is an antibiotic producer, P is antibiotic sensitive, and R is antibiotic resistant.
R is an antibiotic producer, P is antibiotic sensitive, and Q is antibiotic resistant.
P is an antibiotic producer, Q is antibiotic resistant, and R is antibiotic sensitive but evolves resistance during the course of the experiment.
Show Solution
Verified By Collegedunia
The Correct Option isA
Solution and Explanation
Step 1: Understanding the Question:
This question asks to interpret the results of a competition experiment between three bacterial strains (P, Q, and R) grown together, based on a provided population graph.
Step 2: Detailed Explanation:
• Let us analyze the growth trajectories of the three strains over the 10-day period:
itemize
• During the initial phase (Days 0 to 4), all three strains (P, Q, and R) show a typical increase in population size, demonstrating that they are viable in the growth medium.
• After Day 4, the population of strain Q continues to rise and eventually stabilizes at a high carrying capacity.
• In contrast, the populations of both P and R begin to decrease dramatically after Day 4. This simultaneous decline suggests that strain Q is producing a chemical substance, such as an antibiotic, that is toxic to the other strains.
• Strain P continues to decline steadily throughout the remainder of the 10-day experiment, showing that it is highly sensitive to the antibiotic produced by Q.
• Strain R also declines from Day 4 to Day 7. However, after Day 7, its population turns around and increases rapidly, showing a strong recovery.
• Because the nutrients are not limiting, this recovery of R can be explained by the emergence of a mutation conferring resistance to the antibiotic produced by Q. This allows R to grow and replicate despite the presence of Q.
itemize
Step 3: Final Answer:
Therefore, Q is an antibiotic producer, P is antibiotic sensitive, and R is antibiotic sensitive but evolves resistance during the course of the experiment.
