Krebs cycle, also known as Citric Acid Cycle or Tricarboxylic Acid Cycle (TCA cycle), is the second stage of cellular respiration. It occurs in the mitochondrial matrix of eukaryotic cells and converts the products of glycolysis into energy in the form of ATP.

ATP Consumption in Krebs Cycle:
During Krebs cycle, the following reactions take place, leading to the production of energy in the form of ATP and other molecules:
1. Acetyl-CoA formation: Acetyl-CoA is formed from pyruvate, which is produced during glycolysis. This reaction requires the input of 1 ATP molecule.
2. Citrate formation: Acetyl-CoA combines with oxaloacetate to form citrate. This reaction does not require ATP.
3. Isocitrate formation: Citrate is converted to isocitrate. This reaction does not require ATP.
4. α-Ketoglutarate formation: Isocitrate is converted to α-ketoglutarate. This reaction produces 1 ATP molecule.
5. Succinyl-CoA formation: α-ketoglutarate is converted to succinyl-CoA. This reaction requires the input of 1 ATP molecule.
6. Succinate formation: Succinyl-CoA is converted to succinate. This reaction does not require ATP.
7. Fumarate formation: Succinate is converted to fumarate. This reaction does not require ATP.
8. Malate formation: Fumarate is converted to malate. This reaction does not require ATP.
9. Oxaloacetate formation: Malate is converted to oxaloacetate. This reaction does not require ATP.

Thus, in total, 2 molecules of ATP are consumed during the Krebs cycle (1 molecule in step 1 and 1 molecule in step 5).