The answer could be any of the following:
* energy
* sugar
* carbohydrates
* (possibly even) food.
Controlling voluntary body movements, processing information from sense organs, thoughts, and learning abilities.
Thyriod gland is the right answer
The general theory is that mitochondria and chloroplasts began initially as separate cells that were "eaten" by larger cells, but not digested and simply passed on due to their advantages.<span />
