3. It is known that cells settle under gravity, so the distribution of cells can be non-uniform. Let's modify problem #2 so that the cell density varies linearly with depth, from 0 cells/cm at the top of the gel to 2x108 cells/cm at the bottom of the gel. Assume steady state is reached. A) Find the rate at which protein accumulates in the culture medium. B) Find the protein concentration as a function of location z, assuming the medium is well-stirred. For reference, the top and bottom of the gel are set to z=0.3 mm and z = 0 mm, respectively. C) Find the protein flux as a function of z. 4. It is also known that the diffusivity of protein depends slightly on its concentration. Typically, D decreases linearly with increasing concentration, i.e., D = Do Bc, where Do is the protein diffusivity at infinite dilution and is a positive constant. Let's generalize problem #3 to a trench in the region 0