The type of white blood cell that produces histamine in allergic reactions is: MCQ with Answer and Explanation

Explanation:
NAD⁺ (nicotinamide adenine dinucleotide) is a coenzyme derived from vitamin B₃, serving as an electron carrier in redox reactions. Pepsin is an enzyme, collagen a structural protein, hemoglobin a transport protein. Coenzymes are organic non-protein molecules that assist enzymes.

Explanation:
The vertebral column (spine) consists of vertebrae stacked to form a canal that encloses and protects the spinal cord. The skull protects the brain, rib cage the thoracic organs, pelvis the pelvic organs.

Explanation:
Cyclic adenosine monophosphate (cAMP) is a common intracellular second messenger produced by adenylyl cyclase upon hormone receptor activation (e.g., glucagon, adrenaline). It activates protein kinase A, triggering a cascade of cellular responses. Other second messengers include IP₃, DAG, Ca²⁺.