Question

* 3. Anaerobi Anaerobic respiration doesn't require oxygen, but aerobic respiration does. Which stages of cellular respiration are anaerobic? Which are aerobic? How do you know?

Answer 1

Anaerobic respiration does not require oxygen and in the cycle only two ATP's are made i.e. less energy released. There are two pathways which pyruvate formed can go n anaerobic conditions- Lactic acid fermentation and alcoholic fermentation. (please note this happens only when pyruvate cannot enter the mitochondria of the cell due to lack of oxygen and the Kreb cycle cannot function).

Aerobic respiration as the name suggests follows in the presence of oxygen. Post glycolysis, through which the pyruvate is formed, Kreb's cycle and electron transport chain happens in presence of oxygen. This makes 36- 38 ATP's. Hence, aerobic respiration yields more ATP.

• First step of cellular respiration occurs in cytoplasm- Glycolysis. Glucose is converted in to two molecules of pyruvate and total of two ATP is formed. This step is anaerobic.
• Second step is Kreb's cycle if oxygen is present. This makes pyruvate go in the mitochondria for the cycle to continue and forms 1 ATP per cycle. (Note there are two times cycle happens, one for each pyruvate molecule). This cycle is aerobic for another reason as it releases carbon dioxide.
• In case the oxygen is not present Lactic acid fermentation happens leading the fate of pyruvate to get converted in to Lactic acid and two molecules of ATP. Generally seen in muscle cramps when enough oxygen is not present and pyruvate converts in to lactic acid. In case of bacteria and yeast cells alcoholic fermeentation happens and ethyl alcohol and carbon dioxide is produced.
• Assuming the Kreb cycle happens, third stage of cellular respiration is electron transport chain which is aerobic and yeilds 34 ATP. This cycle happens in Intermembrane of mitochondria and NADH and FADH2 produced in glycolysis and Kreb's cycle is used up here as energy carriers. Final electron acceptor is oxygen here which combines with H+ ions to form 2 molecules of water.

NOTE: ETC and KREB cycle is not followed if there is lack of oxygen availability.