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. K+: Potassium (K+) is the most abundant cation in the intracellular fluid (ICF). This is the correct answer.
B. Ca2+: Calcium (Ca2+) is not the most abundant cation in the ICF; it is found in lower concentrations within cells compared to potassium.
C. Cl-: Chloride (Cl-) is the most abundant anion in the extracellular fluid (ECF), not in the intracellular fluid.
D. Na: Sodium (Na) is the most abundant cation in the extracellular fluid (ECF), not in the intracellular fluid.
Correct Answer is D
Explanation
A. Ca2+: prevents the entrance of any more sperm- While calcium ions play a role in the slow block to polyspermy, the fast block involves sodium ions.
B. Na+: prevents the entrance of more Na- The fast block to polyspermy involves sodium ions (Na+), but the depolarization of the egg membrane prevents the entrance of more sperm, not just more Na+.
C. Na+: prevents the entrance of Ca2+. The fast block prevents additional sperm from entering, not calcium ions.
D. Na+: prevents the entrance of any more sperm: The fast block to polyspermy involves the opening of sodium ion channels, leading to depolarization of the egg membrane. This depolarization prevents other sperm from binding to and penetrating the egg.