What directs similar cells to change into a specific organ?

DNA

Explanation:

DNA serve as genetic material in organisms and guides the differentiation of cells into specific organs. Stretch of DNA that code for a protein is called as gene. Expression of specific genes in similar cells makes them to differentiate into specific cell type of specific organ with distinct functions.

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.