The smallest cell in the human body is: MCQ with Answer and Explanation

Explanation:
The question describes sieve elements, which are the conducting cells of the phloem, not xylem. Sieve tube elements are living but lack a nucleus at maturity and have perforated end walls called sieve plates. Xylem vessels and tracheids are dead, hollow, and lack perforated end walls (vessels have perforation plates, but they are not called sieve plates). Xylem parenchyma is living.

Explanation:
Luteinizing hormone (LH) binds to Leydig cells in the testes, stimulating testosterone production. FSH stimulates Sertoli cells for spermatogenesis. GnRH is hypothalamic.

Explanation:
The Rh factor (Rhesus factor) is an inherited protein found on the surface of red blood cells. It was discovered in 1940 by Karl Landsteiner and Alexander Wiener. They immunized rabbits and guinea pigs with the red blood cells of the Rhesus monkey (Macaca mulatta). The serum produced contained antibodies that agglutinated the red blood cells of about 85% of humans. These individuals were designated Rh-positive, and the rest Rh-negative.