Which organelle is responsible for converting high-energy organic molecules into usable energy?

The mitochondrion is the organelle responsible for converting high-energy organic molecules into usable energy, specifically in the form of adenosine triphosphate (ATP). This process is known as cellular respiration, which primarily occurs in the mitochondria. During cellular respiration, glucose and other organic molecules are broken down through a series of biochemical reactions, ultimately resulting in the production of ATP, which serves as the primary energy currency of the cell.

The structure of the mitochondrion, including its inner membrane folds called cristae, provides a large surface area for the necessary biochemical reactions to take place efficiently. This organelle plays a crucial role in energy metabolism, allowing cells to harness energy from nutrients and is vital for various cellular processes such as growth, repair, and maintaining homeostasis.

Other organelles listed serve different functions: the nucleus is the control center of the cell, storing genetic information; chloroplasts are involved in photosynthesis, converting solar energy into chemical energy in plants; and the endoplasmic reticulum is involved in protein and lipid synthesis. While all play essential roles in the cell, the mitochondrion is specifically tasked with energy conversion from organic molecules, making it the correct answer.