The molecule that acts as a second messenger in many hormone signaling pathways is: MCQ with Answer and Explanation

Explanation:
The sternum, or breastbone, is a flat bone located in the center of the chest, to which the ribs attach. The clavicle, commonly known as the collarbone, connects the arm to the body, running horizontally above the first rib. The scapula, or shoulder blade, is a flat, triangular bone located on the upper back, forming the posterior part of the shoulder girdle. All statements are correct.

Explanation:
Nitrogen fixation, the conversion of atmospheric N2 to ammonia, is performed by certain bacteria and cyanobacteria (blue-green algae). Denitrification is the process where denitrifying bacteria convert nitrates in the soil back into nitrogen gas (N2), returning it to the atmosphere. Ammonification is the decomposition of organic nitrogen into ammonia by microbes; nitrification converts ammonia to nitrate. Thus, statements 1 and 2 are correct.

Explanation:
A synapse is a junction between two neurons (or neuron and effector) where neurotransmitters are released to propagate the signal.