Generate an overlapping word between the given two sentences. When you find the overlapping words, they don't have to match exactly, e.g., "survival" and "survive" are valid overlapping words. Little words like "the" or "of" don't count! You must generate significant words which are not the stop words.

Sentence1: Mitosis is cell division. 
Sentence2: mitosis often causes growth.
Mitosis

Sentence1: Nitrogen is found in proteins, nucleic acids, and chlorophyll. 
Sentence2: Life without protein is impossible.
proteins

Sentence1: Vertebrates are animals that have a backbone. 
Sentence2: birds have a backbone.

backbone