Conditional Where Clause Depending On Input Parameter

I am trying to merge 2 pieces( i.e procedures , or stored proc) of sql together.

My simple QueryA

SELECT colA, colB, colC, colD
FROM tableA
WHERE
colD IS NOT NULL

My simple QueryB

SELECT colA, colB, colC, colD
FROM tableA
WHERE
colC IS NOT NULL

I am trying to merge these 2 pieces if sql together by passing a input parameter which will decide which query to run. So if I pass an input parameter QueryA , it will run QueryA. If I pass an imput parameter QueryB, it will run QueryB.

Essentially both my queries are the same besides the where condition. Is there a way to merge it into one query (and not use if conditions and make my storedproc long) and apply the where condition depending on what input parameter is passed in ?

I know it can be done using dynamic SQL construction. But any other ways ?

Also can someone also give in the solution in PL/SQL.

Thanks a bunch.

Jaffery.