Referring to mitochondria or rod-like structures inside cells of the body whose primary functions include the production and regulation of energy.

a spherical or elongated organelle in the cytoplasm of nearly all plant cells, containing genetic material and many enzymes important for cell metabolism, including those responsible for the conversion of food to usable energy.

This relates to small structures inside cells that have specific purposes. Their main purpose is to produce energy and they also contain DNA. Some cells have more mitochodria than others. Eggs destroy the mitochondria of sperm cells that fertilise them.