Osmoregulation refers to

• A. Water and solute balance across membranes
• B. Body temperature
• C. Breathing rate
• D. Digestive enzyme production

Answer: (A)

Osmoregulation is about keeping water and dissolved salts in the body in the right balance across cell membranes. Organisms live in environments where the external salinity can vary, so they regulate how much water enters or leaves their bodies and how ions are taken up or expelled. Water moves by osmosis in response to solute differences, and organisms actively transport salts to maintain a stable internal osmolarity that supports cell function. For example, marine fish drink seawater and actively excrete excess salt to stay hydrated, while freshwater fish conserve salts by absorbing them at the gills and producing dilute urine. This balancing act is what osmoregulation describes. It isn’t about body temperature, breathing rate, or digestive enzyme production.