If you think there has been a bias at play, then that would be grounds for appeal.
But you've not said much about what yhe bias might be, or exactly how it was instantiated, so we don't know if there is an appearance of bias or not.
I do want to say that regardless of the overall thrust of an answer, its not being presented correctly can lead to a fail, and it can do so fairly. So that you might've made the general point but in an insufficient or inappropriate way can still be a legitimate fail.
In the first instance I would have talked to an AA and/or Programme Director about this informally. After that you would have had a better idea about whether an appeal was appropriate. Appeals must also be presented correctly; I've seen lots dismissed on technicalities because of how they've been presented, so getting advice on it prior to submission can really help.
Best of luck with it.