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: an animal requires air for survival. 
Sentence2: It is breathed in by animals and restored to the air by the photosynthesis mechanism of plants.
air

Sentence1: Producers make food from inorganic molecules. 
Sentence2: Decomposition is the breakdown of organic molecules into inorganic molecules.
inorganic

Sentence1: All chemical reactions require activation energy to get started. 
Sentence2: Chemical changes require activation energy to get started.

activation