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 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. Glomerulus is involved in filtering blood but not in producing hypertonic urine.
B. Collecting duct reabsorbs water and concentrates urine, making it hypertonic.
C. Nephron loop (loop of Henle) creates a concentration gradient in the medulla that helps in water reabsorption but is not the primary site for final urine concentration. This option is partially correct but less specific than the collecting duct.
D. Proximal convoluted tubule reabsorbs a significant portion of water and solutes but does not produce hypertonic urine.