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. 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 B
Explanation
A. Mucosa (mucous membrane): The mucosa is the innermost layer of the digestive tract, not the outermost. It includes the epithelium, lamina propria, and muscularis mucosae.
B. Serosa (mesentery): The serosa is the outermost layer of the digestive tract in parts where it is covered by peritoneum. It consists of a thin layer of areolar tissue topped by simple squamous epithelium.
C. Muscularis externa: The muscularis externa is a layer of muscle in the digestive tract, located beneath the serosa. It is not the outermost layer.
D. Submucosa: The submucosa is a layer of connective tissue located between the mucosa and muscularis externa. It is not the outermost layer.