If barriers to entry into a profession were absolute so that entry would not be possible, what would the supply curve look like? What would the supply curve look like if entry into an occupation were...

If barriers to entry into a profession were absolute so that entry would not be possible, what would the supply curve look like? What would the supply curve look like if entry into an occupation were free and easy? Thus, what role do barriers to entry play in explaining relative rates of return to an occupation?