A Petri dish contains populations of two different species of bacteria (V and W). Both are growing and reproducing at the same rate, using the same resources. The conditions are then changed and the rate of growth and reproduction of the population of species V increases.
Which of the following, acting independently, could cause this increase in growth and reproduction rate?
a decrease in temperature
a change in pH
the addition of an antibiotic
A. 1, 2 and 3
B. 2 and 3 only
C. 2 only
D. 1 and 2 only
E. 1 and 3 only
This does not require much explaining. 1 and 2 follow the same principle. Bacteria have different optimum temperatures and different optimum pHs, some prefer hot, some prefer cold, some prefer basic and some prefer acidic. Changing the temperature or pH can increase the rate of growth and reproduction, therefore 1 and 2 are both correct.
What about 3?
This is tricky because normally we assume antibiotics kill off bacteria. This is not always the case though, and there are instances where the addition of an antibiotic can actually promote growth. Let’s take the example of a bacteria that mutate and after the addition of an antibiotic, only a new dominant mutated strain can grow at a much faster rate than normal. As a result, 3 is also correct.