Final answer:
Measuring dry mass is preferable to fresh mass for assessing an organism's biomass because it excludes the variable water content, leading to more accurate results. This method is key for consistency and precision in scientific measurements and is particularly useful for microorganisms with difficult-to-count cells.
Step-by-step explanation:
Measuring the dry mass of an organism is preferred over fresh mass because it provides a more consistent and accurate representation of the organism's biomass. Fresh mass can vary significantly due to the presence of water, which may fluctuate based on the organism's environment and physiological state. By removing the water content through processes like filtration, centrifugation, and drying, scientists can obtain the dry weight, which is solely the mass of the organic material present. This method is particularly useful for organisms such as filamentous microorganisms, where enumerating individual cells might be challenging.
Additionally, measures such as digital scales have dramatically improved the accuracy and precision of weight measurements, providing mass readings to the nearest thousandth of a gram, compared to a mechanical balance. Hence, when assessing the mass for scientific or medical purposes, such as diagnosing obesity or evaluating culture density, the dry mass is more reliable than fresh mass.