The organelle that releases stored energy, primarily from sugars, is the mitochondrion.

Here's why:

* Mitochondria are the "powerhouses" of the cell. They are responsible for cellular respiration, the process that breaks down glucose (a sugar) in the presence of oxygen to produce ATP (adenosine triphosphate).

* ATP is the main energy currency of the cell. It is used to power all sorts of cellular processes, from muscle contraction to protein synthesis.

While other organelles like chloroplasts (in plant cells) also store energy (in the form of sugars produced through photosynthesis), mitochondria are the primary site of energy release from those stored sugars.