The vitamin that is also a hormone, synthesized by the skin upon exposure to sunlight, is: MCQ with Answer and Explanation

Explanation:
Approximately 70% of CO2 is transported in the blood as bicarbonate ions (HCO3-). CO2 diffuses into red blood cells, where it reacts with water to form carbonic acid, catalyzed by the enzyme carbonic anhydrase. Carbonic acid then dissociates into H+ and HCO3-, which moves into the plasma. About 20-25% is carried as carbaminohemoglobin.

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:
Lactobacillus is a lactic acid bacterium that ferments lactose in milk, producing lactic acid that coagulates proteins to form curd. Saccharomyces cerevisiae (baker's yeast) undergoes anaerobic respiration, producing CO2 gas that causes bread dough to rise. Aspergillus niger, a fungus, is widely used in industrial fermentation for the large-scale production of citric acid. All statements are correct.