Should we tell our daughter about her Biological father?

My daughter, who will be 5 in June, only knows my husband (her stepfather) as her dad.  The biological father is not in the picture and is a text book deadbeat.  My husband and I argue about weither or not to tell her about her biological father.  What is in the best interest of our daughter?  She does have the biological fathers last name.  Thank you!

[AHP84]

First of all, does she know that her stepfather is not her biological father?

Secondly, is she asking questions about who she is or where she came from? (Such as, if she knows her stepfather is not her bio father, is she asking about her bio father? Or if she doesn't know her stepfather is not her bio father, is she asking questions about why she looks or feels "different" in some way, for example, the last name difference?)

[LRM1021]

I would only tell her if she, or you could wait until she was about 10. I think at this age its too confusing/ hurtful to try to understand why a parent would not want to be with them and would not do the things a parent is supposed to do. When they are older, they can gain some more perspective, and digest this information easier. Not that it won't hurt then, but with age comes wisdom and tolerance.