Query Regarding TDS & PAN.

Dear sir,
I want to know that, what will be the TAX Liability of an individual who has salary of Rs. 20 lakh
(I) with PAN
(II)without PAN.

I Think if it will come@ 20%, then it will lower than Tax as per Slab,
what is imp. of PAN?

Please reply on urgent basis.

Thankx in advance.