I want you to model a plant as a cylinder, ignoring the end caps. Assume that plant needs carbon dioxide at the same rate that we need oxygen: 14.5 L/hr for a 70kg person. Also assume that the CO2 diffuses across the surface of the ‘blade’ at the same rate O2 diffuses across our skin: the average person gets 2% of their O2 requirements across their skin (1.7m2). The density of people and plants is g.cm3. What maximum radius can this plant reach and get all of its CO2 by diffusion across its surface?

a)    0.52 mm

b)   1.65 mm

c)    0.833 mm

d)   9.60 mm

e)    10.4 mm