When there are different amounts of a substance on either side of the cell membrane, (a) gradient results.

A cell membrane is a delicate sheet that separates one region from another, it selectively or completely allow the passage of different amounts of substance on either side, which a concentration gradient results. An example of this is diffusion where there is a net movement of substance from the area of higher concentration to the area of lower concentration.

hi,

what occurs during a solar eclipse?

there are small tides across earth.

the moon is between earth and the sun.

p.s. im not sure if the first answer is correct because during a solar ecliphse there are spring tides and i dont know if they are the same.

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.