TASK DEFINITION: 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.
PROBLEM: Sentence1: Energy is the fuel for chemical reactions which run the various systems of the body. 
Sentence2: running requires fuel for chemical reactions which run the various systems of the body.

SOLUTION: body

PROBLEM: Sentence1: microbial fuel cells convert chemical energy into electrical energy. 
Sentence2: microbial fuel cells convert chemical energy into kinetic energy.

SOLUTION: cells

PROBLEM: Sentence1: Pictures are formed on the retina, and are then transmitted by the optic nerve to the brain. 
Sentence2: When light enters the eye through the pupil, information is transmitted by the optic nerve to the brain.

SOLUTION:
brain