College Biology Placement Test 2025 – Complete Practice Resource

Cellular respiration primarily occurs in the mitochondria, which are often referred to as the "powerhouses of the cell." This organelle is responsible for converting the biochemical energy stored in glucose and other organic molecules into adenosine triphosphate (ATP), the energy currency of the cell.

The process of cellular respiration involves several stages: glycolysis, the citric acid cycle (also known as the Krebs cycle), and the electron transport chain. While glycolysis occurs in the cytoplasm, the citric acid cycle and the electron transport chain take place in the mitochondria. The inner mitochondrial membrane is where the electron transport chain operates, utilizing oxygen to produce ATP efficiently.

The other parts of the cell mentioned do not play a direct role in cellular respiration. For example, the nucleus is involved in genetic material storage and transcription, ribosomes are responsible for protein synthesis, and the endoplasmic reticulum assists in protein and lipid synthesis but is not directly involved in the conversion of food into energy.