Good point and referencing is not only appreciated, it's necessary on a scientific stack and vital to maintain this site's quality.
- Commenting and downvoting are the primary means to go about this. Downvoting seems to be done sparsely at Bio, but I always highly encourage it; it gives a slight nudge that something is wrong. A comment helps a lot, especially for newbie users. The voting system is the SE approach of expressing answer merit.
- Mods can place banners that state that [additional] references are needed. Hence, flagging may be an option in exceptional[ly bad] cases (note that the community should moderate this site; mods cannot keep a track of every question or answer - hence, flags are necessary to put a post to the attention of the mod team). However, flags should only be used where mod intervention is necessary. Even plain incorrect answers are not flag-worthy; downvoting and commenting and voting for deletion is the way to go. But again, a banner may also do the trick to nudge a user to improve their answer, but only flag after comments and downvotes don't help. Flags aare a last resort.