During birth, an infant is normally stimulated to breathe by_________________.
surfactant
CO2 accumulating in the infant's blood
prostaglandins
an increased O2 level in the infant's new environment
The Correct Answer is B
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.
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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.
Correct Answer is D
Explanation
A. Amino acids; proteins: Amino acids are the end products of protein digestion, not the substrates that are broken down.
B. Polysaccharides; amino acids: Polysaccharides are broken down into simple sugars (monosaccharides), not amino acids.
C. Proteins; nucleotides: Proteins are broken down into amino acids, not nucleotides. Nucleotides are components of nucleic acids, not proteins.
D. Nucleic acids; nucleotides: Nucleic acids (such as DNA and RNA) are broken down into nucleotides.