In which organelle does the Krebs cycle take place?

• A. Cytoplasm
• B. Mitochondria-matrix
• C. Nucleus
• D. Endoplasmic reticulum

Answer: (B)

The Krebs cycle, also known as the citric acid cycle or tricarboxylic acid (TCA) cycle, occurs in the mitochondria, specifically within the mitochondrial matrix. This organelle is often referred to as the powerhouse of the cell due to its role in energy production. The mitochondrial matrix contains the necessary enzymes for the Krebs cycle to function, and it is here that the acetyl-CoA produced from the breakdown of carbohydrates, fats, and proteins enters the cycle to produce energy in the form of ATP, along with reducing equivalents like NADH and FADH2.

In contrast, processes occurring in the cytoplasm primarily involve glycolysis and other metabolic pathways that do not directly include the Krebs cycle. The nucleus is responsible for housing DNA and managing gene expression, while the endoplasmic reticulum is involved in protein and lipid synthesis. Consequently, the intricate processes of cellular respiration, including the Krebs cycle, are localized in the mitochondria where they can effectively contribute to ATP production.