In general, you can look at the pKa (or pKb) of the weak acid (base), and go 1 pH unit above and below that for relatively efficient buffering. Of course, buffer capacity of the particular buffer in use will be important also.
to maintain the pH
Buffering system.
pH balance
A buffer resists pH change.
Phosphate source
pH balance
The chemical buffering system.
IT act as a buffering agent to maintain the PH of a PCR
This depends on what other acids or bases or buffering substances are in solution already, even if pH is neutral!
Buffering system is the physiological system that function to keep pH within normal limits.
Partially, yes. Most of the pH is regulated by respiration (how fast you breath) with the kidneys providing some fine tuning of the buffering ability of the blood.
pH control. In other words, buffering of lysing and extracting matrix to preserve DNA integrity, otherwise compromised in extreme pH.