In which part of the cell does the Krebs cycle occur?

The Krebs cycle, also known as the citric acid cycle or tricarboxylic acid (TCA) cycle, occurs in the mitochondrial matrix of eukaryotic cells. This is an essential metabolic pathway that plays a crucial role in cellular respiration, where it is involved in the oxidative breakdown of carbohydrates, fats, and proteins to produce energy.

The mitochondrial matrix is the innermost compartment of the mitochondria, which houses the enzymes necessary for the Krebs cycle. This environment is conducive to the cycle's reactions, providing the required substrates and maintaining the appropriate conditions for enzymatic activity. The Krebs cycle produces key energy-carrying molecules such as NADH and FADH2, which are later used in the electron transport chain to generate ATP.

Other parts of the cell mentioned in the options do not participate in the Krebs cycle. Ribosomes are the sites of protein synthesis, the cytoplasm contains various cellular components and is where glycolysis occurs, and the nucleus houses genetic material and regulates gene expression but is not involved in energy production. Thus, the mitochondrial matrix is specifically where the Krebs cycle takes place, making it the correct answer.