Scientists are testing substance L to determine how it enters mammalian cells in a culture. The cells maintain a 120 millimolar (mM) intracellular concentration of substance L . The scientists determined the rate of entry of substance L into the cells at various external concentrations of substance L (10 to 100 mM) in culture medium (Table 1). Table 1. Rate of entry of substance L into mammalian cells in culture
External concentration of substance L (mM) Rate of entry of substance L into cell as a percent of maximum
10 5%
20 25%
30 45%
40 65%
50 80%
60 90%
70 95%
80 100%
90 100%
100 100%
The cells maintain substance L at an internal concentration of 120 mM .
Determine the external concentration of substance L that will result in one-half of the maximal entry rate.