Final answer:
A spectrophotometer quantifies bacterial count by measuring the absorbance of light, which correlates to the concentration of bacteria in a sample. It works by passing light through a sample and detecting the intensity of transmitted light, which decreases as bacterial turbidity increases.
Step-by-step explanation:
A spectrophotometer, often abbreviated as 'spec,' is an instrument used to measure the absorbance of light, also referred to as optical density. The principle behind its use in biology is that the amount of light absorbed by a bacterial sample is directly proportional to the concentration of bacteria present. Therefore, the correct answer to the question is that a spectrophotometer quantifies bacterial count.
Spectrophotometers operate by transmitting light through a bacterial cell suspension, with the transmitted light being measured by a detector on the other side. The greater the number of bacteria in the suspension, the higher the turbidity or cloudiness of the sample, which results in less light reaching the detector. This change in light intensity is inversely related to the light transmitted and is used to calculate the absorbance. Measuring turbidity is a quick means to estimate cell density and, with a previously established calibration curve corresponding to standard bacterial counts, spectrophotometric readings can provide fast estimations of bacterial counts in similar samples.