Which of the following enzymes functions at the lowest pH?
Trypsin
Pancreatic amylase
Pepsin
Salivary amylase
The Correct Answer is C
A. Trypsin functions in the small intestine, where the environment is slightly alkaline. Therefore, this enzyme does not function at a low pH.
B. Pancreatic amylase also functions in the small intestine, where the pH is neutral to slightly alkaline.
C. Pepsin functions in the stomach, where the environment is highly acidic (pH 1.5 to 2). Pepsin is the correct answer because it works optimally at this low pH.
D. Salivary amylase functions in the mouth, where the pH is neutral or slightly alkaline.
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Correct Answer is B
Explanation
A. Aerobic respiration; anaerobic fermentation: Aerobic respiration primarily occurs in the mitochondrion, and anaerobic fermentation occurs in the cytoplasm. Therefore, this is incorrect.
B. Glycolysis; the citric acid (Krebs) cycle: Glycolysis occurs in the cytoplasm, breaking down glucose into pyruvate. The citric acid (Krebs) cycle takes place in the mitochondrion, where it further processes pyruvate for energy production.
C. The citric acid (Krebs) cycle; mitochondrial electron-transport: Both the citric acid cycle and the mitochondrial electron transport chain occur in the mitochondrion.
D. Anaerobic fermentation; glycolysis: Glycolysis occurs in the cytoplasm and is the first step in both aerobic and anaerobic pathways, but anaerobic fermentation also occurs in the cytoplasm, so this option is not accurate in distinguishing between processes happening in different locations.
Correct Answer is B
Explanation
A. 20,000 to 30,000: This number is too high for the typical number of sperm that reach the vicinity of the egg.
B. 20 to 200: This number is within the range of the actual number of sperm that typically reach the vicinity of the egg.
C. Half: This is an exaggerated number, as far fewer than half of the ejaculated sperm reach the vicinity of the egg.
D. 2000 to 3000: This number is too high for the typical number of sperm that reach the vicinity of the egg.