I asked my intro biology students, working in groups to analyze parts of the Wolfe-Simon et al. 2011 arsenic life paper, to calculate how much bacterial growth the background level of phosphate would support:
The basal culture medium contained 3 x 10-6 (3 micromolar) phosphate; this level of phosphate was present in the no-phosphate medium used to grow GFAJ-1 cells. Marine bacteria grown under P-limited conditions contain 2 femtograms (2 x 10-15 g) phosphate per cell. How much cell growth will 3 micromolar phosphate support, in cells/mL, assuming that GFAJ-1 has the same phosphate requirements as the marine bacteria? Express your answer to 2 significant digits, in the form “3.7 x 105 cells/ml”
I saw that many were struggling with this question, so I gave the students additional information, that the molar mass of phosphate is 95, that they could round up to 100.
In the end, 51% arrived at a correct solution. Is this good, bad, satisfactory, unsatisfactory?
Only about 20% of the students are Biology majors; the rest are largely engineering majors, some biochemistry, and assorted other majors.