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

Sentence1: infection can cause bodily tissues to swell. 
Sentence2: Bacteria can cause bodily tissues to swell.
bodily

Sentence1: Small temperature variations can have major effects on natural ecosystems. 
Sentence2: volcanic ash in the atmosphere can have major effects on natural ecosystems.

ecosystems