Final answer:
We avoid taking 20 µL from a stock solution and diluting it in 980 µL of buffer in a single step due to potential inaccuracies in measurement at such small volumes.
Step-by-step explanation:
The reason we do not take 20 µL from the original stock solution and dilute it in 980 µL of buffer to achieve a desired concentration in a single step, rather than performing two serial dilutions, is often related to accuracy and precision in the laboratory setting.
When dealing with such small volumes, making a direct dilution from a highly concentrated stock can introduce significant errors. Serial dilutions help mitigate these errors by diluting the stock in a stepwise manner, ensuring that each dilution is within the optimal range for pipetting accuracy.
Moreover, by using serial dilutions, the final concentration of the solution is more accurately known, as each step's dilution factor can be precisely controlled.
This is particularly important for sensitive experiments where the concentration of reactants needs to be precise, such as in DNA or enzyme assays. Additionally, serial dilutions allow for a more thorough mixing of the sample with the diluent, which is crucial for achieving a homogenous solution.