Final answer:
A spectrophotometer is used to measure the total protein of a sample by assessing the color intensity change in a chemical assay, which correlates with protein concentration. The correct option is not mentioned above.
Step-by-step explanation:
The instrument used to measure the total protein of a sample is a spectrophotometer. In biology, the concentration of proteins in a sample can be measured using a chemical assay that changes color in proportion to the amount of protein present, with the color intensity measured by the absorbance reading.
A spectrophotometer can also be used to measure turbidity, which serves as an indirect measure of cell density in microbiological assays.
Additionally, methods like sandwich ELISA use spectrophotometry to quantify specific antigens or proteins by producing a color change that correlates to the protein concentration. The correct option is not mentioned above.