生物界

生 = 牛 + 一 : Mnemonic symbol: a cradle.

Sherlock Holmes (sh) comforts a crying baby bull (牛) in a cradle (生) in front of the engine ((e)ng1) and plays him a tune on a flute (一).

物 = 勿 + 牛 : Willy Walrus (w) wants to become a physicist (物) and does research about dark matter (物) in the space station's bathroom (Ø4). His motivation is to become a super villain and rule the world. Just as he is about to have a breakthrough, a huge black ox (牛) flying with the help of bat wings (勿) hits Willy with an oxerang and takes away the dark matter, saving the world.

界 = 介 + 田 : Joan of Arc wants to leave this world and sets up a rocket launch field in the elevator's bathroom. The field looks like a normal crop field, except that there's a rocket in the middle and that the Joan of Arc marked the boundary with white and red tape.