Final answer:
The death phase is excluded in cell population measurements using 'specs' or spectrophotometric methods because these techniques cannot distinguish between live and dead cells, focusing on overall cell activity instead. The correct answer to the question is a. Death phase is excluded
Step-by-step explanation:
When measuring cell populations using spectrophotometric methods or 'specs', both live and dead cells are usually accounted for because these indirect methods measure overall cell activity rather than the number of viable cells specifically. Parameters such as ATP formation, protein and nucleic acid synthesis, and oxygen consumption are monitored, but they do not specifically distinguish between live and dead cells, thus often excluding the detection of the death phase where cell numbers decrease due to high mortality.
During the death phase, as toxins accumulate and nutrients deplete, cell death exceeds cell division, leading to an overall decline in cell numbers. Some cells may lyse, releasing nutrients into the medium that can help remaining cells survive and potentially form endospores. However, without specialized viability stains that differentiate live from dead cells using fluorescent colors, this phase can go undetected by general spectrophotometric analysis.