Linearity and Excel graphing. Phytoplankton are unicellular photosynthetic organisms which are vital to ocean life and play a major role in regulation of carbon dioxide in the atmosphere. Phytoplankton can be indirectly quantified by measuring the fluorescence of chlorophyll a (Chl a).

Chl a (pg/uL) Signal
4 540
10 1352
20 2481
40 5063
60 7470
90 11111
120 14502
160 18674
200 22196
240 26196
Is the concentration (pg/L)(pg/μL) parts per million, parts per billion, or something else?
a. something else
b. parts per billion
c. parts per million