A researcher prepares a suspension of mitochondria from tissue and monitors the respiration of the mitochondria by the rate of oxygen (O2) consumption in the presence of pyruvate. When the researcher adds an inhibitor of isocitrate dehydrogenase to the suspension, oxygen consumption (respiration) stops.

Answer and explanation:

The mitochondria are the organelle responsible for respiration, which leads to the production of ATP - the most important molecule in energy transfer.

For respiration to happen, there are several processes involving chemical reactions that take place in the mitochondria. These mechanisms are: oxidative decarboxylation, Krebs cycle, and oxidative phosphorylation. Glycolysis is also important for these processes to occur, but this particular case happens outside of the mitochondria.

Pyruvate is an important precursor of the Krebs cycle, also called 'the citric acid cycle'. The researcher observes the functioning of the mitochondria in presence of pyruvate, but then adds an inhibitor of isocitrate dehydrogenase. This inhibitor cancels out the action of the isocitrate dehydrogenase, which is a key enzyme in the Krebs cycle. By inhibiting this enzyme, the cycle cannot continue, and respiration stops.