This thesis investigates the biochemical, biophysical, and quantitative foundations of oxidative stress in living systems, with a specific focus on reactive oxygen species (ROS), mitochondrial metabolism, and the emerging therapeutic use of ultrasound combined with engineered nanoparticles in cancer treatment. The work begins with an overview of cellular structure and function, emphasizing the role of key organelles—particularly mitochondria and the endoplasmic reticulum—in maintaining metabolic homeostasis and regulating redox balance. Cellular respiration is described through anaerobic glycolysis and aerobic metabolism, including the Krebs cycle and oxidative phosphorylation, highlighting how ATP production depends on coordinated electron transport processes. A central theme is the dual role of ROS as both signaling mediators and drivers of oxidative damage.