Kreb’s cycle occurs in the

Step 1: Analyze the question The question asks where the Krebs cycle (also called the citric acid cycle or TCA cycle) takes place in the cell.

Step 2: Explain the concept The Krebs cycle is part of aerobic respiration. Respiration happens in stages:

1. Glycolysis happens in the cytoplasm. Glucose is broken down into pyruvate.
2. Link reaction happens in the mitochondrial matrix. Pyruvate becomes acetyl-CoA.
3. Krebs cycle happens in the mitochondrial matrix. Acetyl-CoA is oxidised, releasing CO₂ and producing NADH, FADH₂ and a little ATP.
4. Electron transport chain happens on the inner mitochondrial membrane (cristae). Most of the ATP is made here.

Step 3: Eliminate the options

• A. Mitochondria: Correct. The enzymes for the Krebs cycle are in the mitochondrial matrix.
• B. Cytoplasm: This is where glycolysis occurs, not the Krebs cycle.
• C. Nucleus: This holds the DNA and controls the cell's activities. It has no role in respiration.
• D. Ribosomes: These make proteins. They are not involved in the Krebs cycle.

Step 4: Answer

Exam tip: Remember that the mitochondrion is the "powerhouse of the cell". Also remember the phrase "Glycolysis is in the Gutter (cytoplasm); Krebs is in the Keep (matrix)". Any question about aerobic respiration steps after glycolysis points to the mitochondria.