What is the name for the protein structures that attach sister chromatids to each other?

Correct Answer: B

Rationale: Centromeres hold sister chromatids together.

Correct Answer: B

Rationale: Second messengers amplify and transmit signals inside the cell.

Correct Answer: B

Rationale: Ligands bind receptors to trigger signaling pathways.

Correct Answer: D

Rationale: Blood group antigens are present on RBC surfaces in fetal blood; they are inherited as dominant Mendelian traits, not recessive.

Correct Answer: B

Rationale: Reticulocytes (young RBCs) show a network when stained; mature RBCs are anucleate and flow faster in capillaries.