BCG vaccine is used to prevent: MCQ with Answer and Explanation

Explanation:
The chorion is the outermost membrane surrounding the embryo. It forms chorionic villi that interdigitate with maternal uterine tissue to form the placenta, facilitating nutrient and gas exchange. The amnion surrounds the embryo, forming a fluid-filled cavity. The yolk sac is involved in early nutrition, allantois forms part of the umbilical cord. The chorion is derived from trophoblast and extraembryonic mesoderm.

Explanation:
In primary succession on a bare, lifeless rock (xerosere), the pioneer species are usually lichens (a symbiotic association of fungi and algae or cyanobacteria). Lichens can survive in harsh, dry conditions and secrete acids that slowly weather the rock, contributing to soil formation. Once a thin layer of soil is formed, mosses can colonize, followed by herbs, grasses, shrubs, and eventually a climax forest community.

Explanation:
The tricuspid valve (right atrioventricular valve) has three cusps and closes during ventricular systole to prevent regurgitation into the right atrium. The bicuspid (mitral) is on the left side. Aortic and pulmonary valves are semilunar valves at the ventricular outlets.