Final answer:
Counts of bacterial colonies on a plate should be between 30 and 300 to ensure statistical reliability and accurate measurement of colony-forming units (CFU).
Step-by-step explanation:
When counting colonies on a plate, the number must be between 30 and 300 colonies for the count to be statistically reliable and to ensure accurate counting.
This range also helps to minimize the occurrence of more than one bacterial cell forming a single colony, so the calculated colony-forming units (CFU) is closer to the true number of live bacteria in the population.
Counting colonies accurately is crucial in experiments to estimate the number of bacteria present in a culture or sample using serial dilution methods and plating techniques like the pour plate method and the spread plate method.