Biology Forums - Study Force

1. Many cells/organisms can withstand periods of oxygen debt (anaerobic conditions). Animals undergoing oxygen debt convert pyruvic acid to lactic acid. Pyruvic acid is fairly nontoxic in even high concentrations. However, lactic acid is toxic in even moderate concentrations. Explain why this conversion occurs in organisms.



2. In the absence of oxygen, what do you think would happen to ATP synthase activity/ATP production if you decreased the pH of the
intermembrane space of the mitochondrion?


3.  All living organisms require a constant supply of ATP to maintain life. If no light is available, how can a plant make ATP?



4. How many ATP and NADPH molecules are consumed in the formation of 4 molecules of glyceraldehyde-3-phosphate by the Calvin cycle?

1. C6H12O6 = 2 C2H5OH + 2CO2 + Energy

This is the conversion from glucose to ethanol + carbon dioxide + energy. The reason this conversion occurs is because by breaking down the pyruvic acid (2 glucose), it can temporarily obtain some oxygen to use. These organisms therefore use the 2 pyvuric acid molecules to make energy, and while they are at it, they also create 2 carbon dioxide molecules and ethanol. So you see, the ethanol is a byproduct of a cell desperately trying to obtain oxygen to survive. Even though a cell is documented to stay alive in anaerobic conditions, most aerobic cells cannot truly survive without oxygen. They cannot EVER be considered anaerobic, because to be anaerobic, a cell doesn't need oxygen. Aerobic cells like yeast can survive by using up its reserves of oxygen that it has saved in the form of glucose. Glucose then turns to pyvuric acid, then ethanol.

2. Because addition of H+ (lowering the pH) would establish a proton gradient even without the function of the electron transport chain, we would expect ATP synthase to function and synthesize ATP.

3. Keep in mind that it is not always light and that not all cells of a plant are directly exposed to light. For example, cells on the interior of a plant stem and those in the roots have little, if any, exposure to light. Plants, like other eukaryotic organisms on Earth, also contain mitochondria. Plant cells undergo glycolysis in the cytoplasm and transfer acetyl CoA to mitochondria, where it enters the Krebs cycle. The NADH and FADH2 produced during the Krebs cycle then undergo oxidative phosphorylation to produce ATP.

4. 6NADPH + 9ATP -> 1G3P
36NADPH + 54 ATP -> 6 G3P