In the presence of oxygen, the three-carbon compound pyruvate can be catabolized in the citric acid cycle. First, however, the pyruvate (1) loses a carbon, which is given off as a molecule of CO2, (2) is oxidized to form a two-carbon compound called acetate, and (3) is bonded to coenzyme A. Which of the following sets of products result from these reactions?
A) acetyl CoA, FADH2, and CO2
B) acetyl CoA, NADH, and CO2
C) acetyl CoA, NAD+, ATP, and CO2
D) acetyl CoA, O2, and ATP
The citric acid cycle.
Starting with citrate, which of the following combinations of products would result from three acetyl CoA molecules entering the citric acid cycle?
A) 3 ATP, 6 CO2, 9 NADH, and 3 FADH2
B) 1 ATP, 2 CO2, 3 NADH, and 1 FADH2
C) 6 ATP, 6 CO2, 3 NADH, and 12 FADH2
D) 3 ATP, 3 CO2, 3 NADH, and 3 FADH2
New biosensors, applied like a temporary tattoo to the skin, can alert serious athletes that they are about to "hit the wall" and will find it difficult to continue exercising. These biosensors monitor lactate, a form of lactic acid, released in sweat during strenuous exercise. Which of the statements below is the best explanation of why athletes would need to monitor lactate levels?
A) During anaerobic respiration, lactate levels increase when muscles cells need more energy; however, muscles cells eventually fatigue, thus athletes should modify their activities to increase aerobic respiration.
B) During anaerobic respiration, muscle cells receive too little oxygen and begin to convert lactate to pyruvate (pyruvic acid), thus athletes experience cramping and fatigue.
C) During aerobic respiration, muscle cells cannot produce enough lactate to fuel muscle cell contractions, and muscles begin to cramp, thus athletic performance suffers.
D) During aerobic respiration, muscles cells produce too much lactate, which causes a rise in the pH of the muscle cells, thus athletes must consume increased amounts of sports drinks, high in electrolytes, to buffer the pH.
In the absence of oxygen, yeast cells can obtain energy by fermentation, which results in the production of which of the following sets of molecules?
A) ATP, CO2, and ethanol (ethyl alcohol)
B) ATP, CO2, and acetyl CoA
C) ATP, NADH, and ethanol
D) ATP, CO2, and lactate