The carbon dioxide we exhale is produced in
a. glycolysis.
b. the electron transport system.
c. lactate fermentation.
d. the citric acid cycle.
The correct answer and explanation is:
The correct answer is d. the citric acid cycle.
Carbon dioxide (CO2) is produced during the citric acid cycle (also known as the Krebs cycle), which is a key step in cellular respiration. This process takes place in the mitochondria of eukaryotic cells, and its primary purpose is to generate energy through the oxidation of acetyl-CoA, which is derived from carbohydrates, fats, and proteins.
During the citric acid cycle, acetyl-CoA enters the cycle and combines with a molecule called oxaloacetate to form citric acid. This molecule undergoes a series of chemical reactions that ultimately result in the production of ATP, NADH, and FADH2, which are essential for the next step in cellular respiration, the electron transport chain. During these reactions, two molecules of carbon dioxide are released for each acetyl-CoA molecule that enters the cycle. This CO2 is a waste product that is expelled from the cell and eventually exhaled by the organism.
While glycolysis, the electron transport system, and lactate fermentation are all part of cellular metabolism, they do not produce carbon dioxide directly. Glycolysis, which occurs in the cytoplasm, breaks down glucose into pyruvate without the release of CO2. The electron transport system is responsible for generating a proton gradient used to produce ATP, and lactate fermentation occurs when oxygen is scarce, converting pyruvate into lactate, without generating CO2.
Thus, the citric acid cycle is the correct answer since it is directly responsible for the production of CO2 that we exhale.