What is the principal cation of the ECF?
Na+
Ca2+
CL-
K+
The Correct Answer is A
A. Na+: Sodium (Na+) is the principal cation in the extracellular fluid (ECF), which includes interstitial fluid and blood plasma.
B. Ca2+: Calcium (Ca2+) is important in various bodily functions but is not the principal cation in the ECF. Sodium is more predominant in ECF.
C. Cl-: Chloride (Cl-) is the principal anion in the ECF, not a cation. Sodium is the principal cation.
D. K+: Potassium (K+) is the principal cation in the intracellular fluid (ICF), not the ECF. Sodium is the principal cation in the ECF.
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Correct Answer is A
Explanation
A. Y chromosome: The SRY gene on the Y chromosome codes for the testis-determining factor (TDF), which initiates the development of testes and male characteristics.
B. Gonadal ridges: The gonadal ridges are the precursor structures that develop into gonads but do not contain the gene for TDF.
C. X chromosome: The X chromosome contains genes important for development but does not code for TDF.
D. Fetal testes: The fetal testes produce testosterone but are not the source of the TDF gene.
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.