The net force driving an uncharged molecule across the plasma membrane by passive transport is:
(a) concentration gradient
(b) charge of the molecule
(c) membrane potential
(d) more than one is correct

(a) Concentration gradient

Explanation:

The concentration gradient refers to the differences in the concentration of a substance across the plasma membrane. The passive transport of uncharged particles across the membrane is driven by differences in their concentration on either side of the membrane. The direction of the movement is down the concentration gradient.  

For example, passive transport of water across the membrane (osmosis) occurs from the region of its higher concentration to that of the lower concentration.  

the organisms are not adapted to live in some communities or habitats.