In a small East German town shortly before the fall of the Berlin Wall, Ulla, a sensitive and principled 10th-grader, meets computer-obsessed Winfried, son of a chemical plant manager. On a field trip with her biology class, Ulla discovers that a trout farm and weekend homes are being built illegally in a local conservation area. The situation gets complicated when she discovers that Winfried’s family is responsible. She nevertheless passionately agitates to stop the construction project, even soliciting Winfried to help her create a touched-up photograph of a rare bird as "evidence" that the conservation area is home to an endangered species. When Ulla's deception is discovered, she faces serious consequences.

Biology! was one of very few East German feature films to address environmental issues. The topic was taboo in the GDR and all data on environmental damages was classified. In the 1980s, grassroot activists nevertheless began a vigorous environmental movement.