Questions: Rank the following processes by the amount of adenosine triphosphate (ATP) produced per substrate, from most ATP to least. Krebs cycle (from one Acetyl-CoA) Fermentation (from one pyruvate) Glycolysis (from one glucose) Electron Transport Chain

To rank the processes by the amount of ATP produced per substrate, we need to consider the ATP yield of each process:

1. Electron Transport Chain (ETC): The ETC is the final stage of cellular respiration and produces the most ATP. It generates approximately 28-34 ATP molecules per glucose molecule, but since the question asks for ATP per substrate, we consider the input from NADH and FADH2. Each NADH can produce about 2.5 ATP, and each FADH2 can produce about 1.5 ATP. The ETC itself doesn't have a single substrate like the others, but it is the stage where the majority of ATP is produced.

2. Krebs Cycle (from one Acetyl-CoA): The Krebs cycle, also known as the citric acid cycle, produces 1 ATP (or GTP) directly per Acetyl-CoA. However, it also generates 3 NADH and 1 FADH2 per Acetyl-CoA, which are used in the ETC to produce additional ATP. In total, the Krebs cycle contributes to the production of approximately 10 ATP per Acetyl-CoA when considering the subsequent ATP generation in the ETC.

3. Glycolysis (from one glucose): Glycolysis produces a net gain of 2 ATP molecules per glucose molecule. It also produces 2 NADH, which can be used in the ETC to generate additional ATP, but the direct ATP yield from glycolysis itself is 2 ATP.

4. Fermentation (from one pyruvate): Fermentation occurs in the absence of oxygen and does not produce additional ATP beyond what is generated in glycolysis. It primarily serves to regenerate NAD+ from NADH, allowing glycolysis to continue. Therefore, fermentation itself does not produce ATP from pyruvate.

Ranking from most ATP to least:

1. Electron Transport Chain
2. Krebs Cycle (from one Acetyl-CoA)
3. Glycolysis (from one glucose)
4. Fermentation (from one pyruvate)

In summary, the Electron Transport Chain produces the most ATP, followed by the Krebs Cycle, Glycolysis, and finally Fermentation, which does not produce additional ATP.