I-485 is approved. It is similar to H1b. One can extend
his/her H1b even he/she has filed I-485. But keep
one thing in mind, after submitting I-485,
it is probably hard to get a new F1 "visa" to
enter US. You are now in US and don't need to apply
F1 visa for entry purpose. Just stay in US before
your I-485 is approved. I am not a lawyer. So you
can ask a lawyer to have peace of mind.