The compound that is the main energy source for the brain is: MCQ with Answer and Explanation

Explanation:
B lymphocytes (B cells) differentiate into plasma cells that produce and secrete antibodies (immunoglobulins) specific to antigens, providing humoral immunity. T cells are involved in cell-mediated immunity. Erythrocytes carry oxygen, platelets clot blood, monocytes differentiate into macrophages that phagocytose pathogens. Lymphocytes are a type of white blood cell.

Explanation:
Motilin is a peptide hormone secreted by the Mo cells (or M cells) in the crypts of the duodenum and jejunum. Its secretion occurs in cycles during the fasting (interdigestive) state. Its primary function is to stimulate gastric motility and emptying, and to initiate and regulate the Migrating Motor Complex (MMC). The MMC is a pattern of electromechanical activity observed in the gastrointestinal tract during fasting, characterized by waves of contraction that sweep undigested material, bacteria, and sloughed cells from the stomach and small intestine towards the colon, acting as a 'housekeeper'.

Explanation:
Myoglobin is a red protein in muscle cells that stores oxygen and facilitates its diffusion during muscle contraction. It has a higher affinity for O₂ than hemoglobin, allowing oxygen transfer from blood to muscle. Hemoglobin is in RBCs, hemocyanin is in some invertebrates, cytochromes are electron carriers.