Osmosis moves water from areas of low solute concentration to areas of high solute concentration.

A. Muscles and fat: While skeletal muscle contains about 75% water, adipose tissue is uniquely hydrophobic and contains very little water (approximately 10%). A high proportion of fat significantly reduces the total body water percentage. This combination does not represent the highest overall hydration level.

B. Bones and muscles: Cortical bone is relatively dry, containing only about 20% to 30% water within its calcified matrix. While muscle is highly hydrated, the low water content of bone pulls the average down. Soft, metabolically active visceral organs contain much higher percentages of fluid.

C. Kidneys and brain: These organs are highly vascularized and metabolically active, consisting of approximately 80% to 85% water. The brain requires a high fluid content for signaling and protection, while the kidneys process the body's entire fluid volume. They represent the most aqueous tissues in the body.

D. Teeth and skin: Tooth enamel is the hardest and driest substance in the human body, containing almost no water. The skin provides a protective barrier and contains significantly less water than internal organs to prevent excessive evaporative loss. This pair contains the least hydrated tissue in the body.

False: Aqueous secretions including saliva, gastric juice, and succus entericus are essential for the enzymatic hydrolysis of nutrients. Proper hydration ensures adequate production of these digestive fluids to facilitate motility and absorption. Dehydration leads to constipation and impaired nutrient uptake.