Quantitative Reasoning – an example

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.

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About jchoigt

I'm an Associate Professor in the School of Biology at Georgia Tech, and Faculty Coordinator of the Professional MS Bioinformatics degree program.
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