Biological is related to Grow. Grow is related to Crop. 
Flower is related to Used. Used is related to Oil. Oil is related to Pipe. Elbow is a type of Pipe. 
Biological <--RelatedTo--> Grow <--RelatedTo--> Crop 
Flower <--RelatedTo--> Used <--RelatedTo--> Oil <--RelatedTo--> Pipe <--IsA-- Elbow 