Question

The type of chemical influencing cell division and elongation:

Answer 1

Auxin. 
Auxin is a plant hormone produced in the stem tip that promotes cell elongation. Auxin moves to the darker side of the plant, causing the cells there to grow larger than corresponding cells on the lighter side of the plant.

source: https://www2.estrellamountain.edu/faculty/farabee/biobk/BioBookPLANTHORM.html