A bioreactor with a reaction container (1, 1a, 1b, 1c) for a substance (C) to be acted upon with a medium has a pump (5, 5a, 5b, 5c, 5d) for conveying the medium. The pump is designed as an expendable pump or, respectively, parts (53d, 54d, 55d) of the pump are designed as expendable parts.