Cellular respiration and mitochondria work together as the powerhouse systems that generate energy in living cells. This complex process involves multiple stages that break down glucose to produce ATP, the energy currency of cells.

The process begins with glycolysis in the cell's cytoplasm, where glucose is split into pyruvate molecules. In the presence of oxygen, these molecules enter the mitochondria for aerobic cellular respiration, moving through the citric acid cycle and electron transport chain to maximize ATP production. When oxygen is unavailable, cells can switch to fermentation, an anaerobic process that produces less energy but allows cells to continue functioning. The key difference between cellular respiration and fermentation is that respiration requires oxygen and produces more ATP, while fermentation occurs without oxygen and yields less energy.

Mitochondria play a crucial role as the site where most ATP is generated during cellular respiration. These specialized organelles contain their own DNA and have a unique double membrane structure that supports the electron transport chain. The inner membrane is highly folded into cristae, increasing the surface area for ATP production. Understanding these processes is essential in biology, as they explain how organisms obtain energy from food molecules. In plants, both cellular respiration and fermentation can occur, though plants primarily use photosynthesis to produce glucose during daylight hours. This glucose can then be used in cellular respiration or stored for later use. The efficiency of these energy-producing pathways varies, with aerobic respiration producing up to 38 ATP molecules per glucose molecule, while fermentation only yields 2 ATP molecules.