Terumah nullifies orlah, and orlah nullifies terumah. How so? A seah of terumah fell into one hundred, and subsequently three kabin of orlah, or three kabin of kilei hakerem fell in, this is where terumah nullifies orlah, and orlah nullifies terumah.

Terumah, and terumas maaser of demai, challah, and bikkurim, are nullified in one hundred and one, and they combine with one another, and one must remove.  Orlah and kilei hakerem are nullified in two hundred and one, and they combine with one another, but one does not need to remove. R' Shimon says: They do not combine. R' Eliezer says: They combine to give flavor, but not to prohibit.