The leaven of malice and wickedness.

My son has just told me that as part of a science experiment he has to write up the ethics of using yeast because it’s alive. I wonder does this mean that a true vegetarian should give up bread and alcoholic drinks. I wonder does yeast have a consciousness is it thinking oh no not the oven when I wanted to drown in alcohol? Of course the real question here is what is the lowest level of consciousness where one should have a sense of moral responsibility for the use of a living thing?