What is the principal cation of the ECF?
Na+
Ca2+
CL-
K+
The Correct Answer is A
A. Na+: Sodium (Na+) is the principal cation in the extracellular fluid (ECF), which includes interstitial fluid and blood plasma.
B. Ca2+: Calcium (Ca2+) is important in various bodily functions but is not the principal cation in the ECF. Sodium is more predominant in ECF.
C. Cl-: Chloride (Cl-) is the principal anion in the ECF, not a cation. Sodium is the principal cation.
D. K+: Potassium (K+) is the principal cation in the intracellular fluid (ICF), not the ECF. Sodium is the principal cation in the ECF.
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Correct Answer is B
Explanation
A. Surfactant reduces surface tension in the alveoli, aiding in lung expansion, but it does not directly stimulate breathing.
B. CO2 accumulating in the infant's blood: The accumulation of CO2 in the infant's blood is a significant stimulus for the first breath after birth. High levels of CO2 trigger the infant's respiratory centers to start breathing.
C. Prostaglandins are involved in labor and delivery but do not directly stimulate breathing in the newborn.
D. An increased O2 level in the infant's new environment: Increased O2 levels do not directly stimulate breathing; rather, the accumulation of CO2 is the primary stimulus.
Correct Answer is C
Explanation
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.