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 A
Explanation
A. Monozygotic; dizygotic: Monozygotic twins are identical twins that result from the division of a single fertilized egg. Dizygotic twins, or fraternal twins, result from the fertilization of two separate eggs.
B. Dizygotic; monozygotic: This is the reverse of the correct order. Dizygotic twins come from two eggs, and monozygotic twins come from one egg.
C. Monozygotic; identical: Monozygotic twins are identical, but this choice does not mention dizygotic twins, which makes it incomplete.
D. Dizygotic; nonidentical: While dizygotic twins are nonidentical, this choice does not properly define the types of twins produced by a single egg (monozygotic).
Correct Answer is B
Explanation
A. 20,000 to 30,000: This number is too high for the typical number of sperm that reach the vicinity of the egg.
B. 20 to 200: This number is within the range of the actual number of sperm that typically reach the vicinity of the egg.
C. Half: This is an exaggerated number, as far fewer than half of the ejaculated sperm reach the vicinity of the egg.
D. 2000 to 3000: This number is too high for the typical number of sperm that reach the vicinity of the egg.