生物媒介

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.

媒 = 女 + 某 : Mahatma Gandhi (m) hired a match-maker (媒) to find a wife for him. The match-maker finally found Bessy Coleman (女), and for their wedding just inside the Eiffel Tower's kitchen (ei2) the match-maker plays "somewhere over the rainbow" on her ukulele (某) for them.

介 = 人 + 丿 + 丨 : Mnemonic symbol: 介 looks like a rocket 🚀. Neanderthal Man (人) and Joan of Arc (ji) are preparing a rocket (介) for its start. Between (介) the layers of the outer shell (介) they are stuffing bananas (丿) and dinosaur bones (丨).