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.

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

A: cell
****
Q: Sentence1: Amphibians have permeable skin that easily absorbs substances from the environment. 
Sentence2: Some substances are harmful to the body and block biological systems.

A: substances
****
Q: Sentence1: Complex chemistry is needed to carry out all the functions of life. 
Sentence2: Steroids are needed to control life functions.

A:
functions
****