How many factors affect nutrient uptake?

[J.J.Luck]

Dear all,

I would be most interested in hearing if there are any factors affecting 
the rate of nutrient uptake by cells that I haven`t thought of.

Here is the list of factors I have already considered:

Nutrient concentration in cell/cell medium
Molecular size of nutrient
Osmotic potential of cell
Rate of active transport into cell
Temperature of surroundings

Thank you in advance for your kind help.

Jason
bsu416 at bangor.ac.uk