Determining the osmolarity and tonicity of a cell Consider a cell with urea concentration inside being 2mmol/L and outside being 2.5mmol/L. The cell itself is permeable to both urea and water. Ignoring the effect of other osmolytes, A) Urea flows in, water flows out B) Urea flows in, water flows in C) Urea flows out, water flows out D) Urea flows out, water flows in I'm confused because I thought water would simply flow out of the cell to equate the concentrations inside and outside such that there is no net flow in urea.

The efflux of water isn't instantaneous. Since urea is free to move across the membrane, it will (and with a net movement from higher to lower concentration).