Final answer:
The plate count method, spectrophotometer, and Petroff-Hausser cell counter all measure cell concentrations, but in different ways.
Step-by-step explanation:
If you calculated your cell concentrations using the plate count method, a spectrophotometer, and a Petroff-Hausser cell counter, the values would be different because each method measures cell concentrations differently.
The plate count method involves diluting a sample and spreading it on agar plates. The number of colonies that grow on the plates is then counted and used to estimate the original cell concentration.
A spectrophotometer measures the turbidity (cloudiness) of a liquid culture, which increases as the number of cells in the culture increases. The turbidity readings can be correlated to cell densities using a calibration curve.
A Petroff-Hausser cell counter is a device that uses a special slide with squares of known areas to count bacterial cells under a microscope. By counting cells in multiple squares and determining the volume observed, the concentration of cells in the original sample can be estimated.