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. It stimulates angiotensin II secretion: Antidiuretic hormone (ADH) does not directly stimulate angiotensin II secretion; instead, it acts on the kidneys to promote water reabsorption.
B. It promotes water conservation: ADH promotes water conservation by increasing water reabsorption in the kidneys, reducing urine output, and thus helping to maintain fluid balance.
C. It inhibits salivation and thirst: ADH does not inhibit salivation or thirst; in fact, it can increase thirst to encourage fluid intake when dehydration is detected.
D. It stimulates hypothalamic osmoreceptors: While ADH affects hypothalamic osmoreceptors indirectly by promoting water retention, its primary function is to act on the kidneys to conserve water.
Correct Answer is D
Explanation
A. Ca2+: prevents the entrance of any more sperm- While calcium ions play a role in the slow block to polyspermy, the fast block involves sodium ions.
B. Na+: prevents the entrance of more Na- The fast block to polyspermy involves sodium ions (Na+), but the depolarization of the egg membrane prevents the entrance of more sperm, not just more Na+.
C. Na+: prevents the entrance of Ca2+. The fast block prevents additional sperm from entering, not calcium ions.
D. Na+: prevents the entrance of any more sperm: The fast block to polyspermy involves the opening of sodium ion channels, leading to depolarization of the egg membrane. This depolarization prevents other sperm from binding to and penetrating the egg.