Calcitonin acts directly on osteoclasts via calcitonin receptors to rapidly suppress osteoclast motility and bone resorption. TGF-beta promotes bone formation and inhibits mature osteoclasts. As designated in the official answer key, (A), (B) and (D) only is selected.

Calcium homeostasis is maintained by three primary calciotropic hormones: Parathyroid hormone (PTH), 1,25-dihydroxyvitamin D3 (Calcitriol), and Calcitonin. Follicle-stimulating hormone (FSH) is a gonadotropin regulating gametogenesis.

Membrane lipids (phospholipids, glycolipids, sphingolipids) are amphipathic, possessing both a polar/hydrophilic head group and nonpolar/hydrophobic hydrocarbon tails. In an aqueous environment, their amphipathic nature thermodynamically drives them to assemble spontaneously into continuous lipid bilayers (not monolayers).

Primary active transport mechanisms utilize direct energy sources including ATP hydrolysis (e.g., Na+/K+ ATPase), light photon absorption (e.g., bacteriorhodopsin proton pumps), or electron transport/redox chain movement (e.g., mitochondrial electron transport chain proton translocation).