What do the terms ‘depletion region’ and ‘barrier potential' mean for a $p-n$ junction?

In a transistor, the doping level in the base is increased slightly. How will it affect

$\left(\mathrm{i}\right)$ collector current and 

In a transistor, doping level in base is increased slightly. How will it affect

$\left(\mathrm{ii}\right)$ base current.

What happens to the width of depletion layer of a $p-n$ junction when it is

(i) forward biased 

What happens to the width of depletion layer of a $p-n$ junction when it is

 (ii) reverse biased?