I can not think of a riddle to help me remember mitochondrion cytoplasm endoplasmic reticulum and organelle
Sorry, I can't think of a riddle either, but what about a mneumonic? Here's one, beginning each word as the words you want to remember. Feel free to change anything to make it more meaniful to you:
Mi (purposely misspelled) cycle endures reticence and organization.
Sra