Extracellular fluid in adults differs from intracellular fluid in that its

Correct Answer: D

Rationale: Extracellular fluid has a higher sodium:potassium ratio (e.g., 140:4 mEq/L) compared to intracellular fluid (e.g., 10:140 mEq/L) due to the sodium-potassium pump.

Correct Answer: C

Rationale: Anti-A/B antibodies (IgM) don't cross the placenta; they develop postnatally and can agglutinate, not necessarily lyse, RBCs.

Correct Answer: A

Rationale: Group B recipients have anti-A antibodies, causing a reaction; AB are universal recipients.

Correct Answer: C

Rationale: Aldosterone retains Na+, expanding ECF and blood volume; common post-surgery.

Correct Answer: B

Rationale: Companion cells are narrow, elongated, thin-walled, living cells which are on the sides of the sieve tubes through plasmodesmata and do not have perforated cell walls.