In cellular respiration, the steps following glycolysis depend on whether oxygen is present.
Select the BEST explanation:
a
Regardless if oxygen is present or not, the production of acetyl-CoA, the citric acid cycle, and electron transport chain follow in order.
b
If oxygen is present, production of acetyl-CoA, the citric acid cycle, and electron transport chain follow in order. If no oxygen is present, photosynthesis occurs starting with Photosystem II.
c
If oxygen is present, production of acetyl-CoA, the citric acid cycle, and electron transport chain follow in order. If no oxygen is present, either lactic acid fermentation or alcoholic fermentation follows.
d
In the presence of oxygen, carbon fixation occurs during the Calvin cycle, when a carbon atom from atmospheric carbon dioxide is added to a 5-carbon sugar.
c
If oxygen is present, production of acetyl-CoA, the citric acid cycle, and electron transport chain follow in order. If no oxygen is present, either lactic acid fermentation or alcoholic fermentation follows.
c
If oxygen is present, production of acetyl-CoA, the citric acid cycle, and electron transport chain follow in order. If no oxygen is present, either lactic acid fermentation or alcoholic fermentation follows.
The correct explanation is option c: If oxygen is present, production of acetyl-CoA, the citric acid cycle, and electron transport chain follow in order. If no oxygen is present, either lactic acid fermentation or alcoholic fermentation follows.
To understand the steps following glycolysis in cellular respiration, we need to consider the presence or absence of oxygen.
If oxygen is present, the next step is the production of acetyl-CoA. This occurs in the mitochondria, where pyruvate, the product of glycolysis, is converted into acetyl-CoA. Acetyl-CoA then enters the citric acid cycle, also known as the Krebs cycle or TCA cycle, which takes place in the mitochondria as well. The citric acid cycle further breaks down the acetyl-CoA, releasing carbon dioxide and producing energy-rich molecules in the form of NADH and FADH2.
Following the citric acid cycle, the electron transport chain takes place in the inner mitochondrial membrane. This stage uses the electrons carried by NADH and FADH2 to produce ATP through oxidative phosphorylation. Oxygen acts as the final acceptor of the electrons, combining with hydrogen ions to form water. This process is called aerobic respiration and is the most efficient way to produce ATP.
However, if no oxygen is present, the cells undergo fermentation to obtain energy. In the absence of oxygen, two common types of fermentation may occur: lactic acid fermentation and alcoholic fermentation. Lactic acid fermentation occurs in some bacteria and our muscle cells when they lack oxygen. It converts pyruvate into lactic acid, regenerating NAD+ in the process. Alcoholic fermentation, on the other hand, occurs in yeast and some bacteria. It converts pyruvate into ethanol and carbon dioxide, also regenerating NAD+.
Therefore, depending on the presence or absence of oxygen, the steps following glycolysis in cellular respiration can lead to the production of acetyl-CoA, the citric acid cycle, and the electron transport chain if oxygen is present, or to fermentation processes if oxygen is absent. The correct answer is option c.