WHERE DOES CELLULAR RESPIRATION OCCUR

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Cellular respiration primarily occurs in the mitochondria of a cell. Here's a step-by-step breakdown:

1. Glycolysis: This is the first step of cellular respiration and it occurs in the cytoplasm. During glycolysis, one molecule of glucose (a six-carbon sugar) is broken down into two molecules of pyruvate (a three-carbon compound).

2. Transition Reaction: This step occurs when the pyruvate molecules produced from glycolysis enter the mitochondria. Here, each pyruvate molecule is converted into a molecule called Acetyl CoA, which is used in the next step.

3. Krebs Cycle (Citric Acid Cycle): This step occurs in the matrix of the mitochondria. The Acetyl CoA produced in the transition reaction enters the Krebs Cycle, where it is broken down into carbon dioxide and high-energy electron carriers.

4. Electron Transport Chain: This is the final step of cellular respiration and it occurs in the inner mitochondrial membrane. The high-energy electron carriers produced in the Krebs Cycle pass their electrons to the electron transport chain, which uses these electrons to produce ATP, the main energy currency of the cell.

So, while the initial step of cellular respiration (glycolysis) occurs in the cytoplasm, the majority of the process (the transition reaction, Krebs Cycle, and electron transport chain) occurs in the mitochondria.