Serial dilutions performed with the same factor cause what kind of change in concentration?

• A. Exponential decrease
• B. Linear increase
• C. No change
• D. Random variation

Answer: (A)

Constant-factor serial dilutions reduce concentration by the same ratio at each step, so the concentration falls exponentially as you perform more steps. With a dilution factor of, for example, 10, each step leaves 1/10 of the previous concentration. After n steps, the concentration is the starting amount divided by 10^n. This exponential decay happens because the change compounds with each dilution, unlike a linear decrease which would subtract a constant amount. It’s also not random variation, since a properly performed dilution follows a precise ratio. For instance, starting at 1.0 and doing successive tenfold dilutions gives 0.1, then 0.01, then 0.001, and so on.