Final answer:
The human body's water composition ranges from about 75% in infants to 50-60% in adults and can decrease to 45% in old age, with organs like the brain and kidneys being particularly high in water content.
Step-by-step explanation:
The percentage of water in the human body varies throughout different stages of life. Infants have a higher water content, around 75% of their body mass, while adults generally have a water composition of 50-60%. These percentages change due to the different proportions of organs, muscles, fat, bone, and other tissues as people age. In senior adults, the water content can decrease to as low as 45%. Furthermore, different organs have various water contents, with the brain and kidneys comprising 80-85% water, and teeth containing the least amount of water, ranging from 8-10%.
Water is not only abundant in the body but also crucial for its functioning. It is a major component of both intracellular and extracellular fluids, with intracellular fluid making up about 50% of a lean person's body weight. In contrast, extracellular fluids account for approximately 20% of the body weight, which includes interstitial fluid and blood plasma. Water is essential as it enables osmosis, the movement of water through semi-permeable membranes, facilitating various cellular processes and the maintenance of solute balance within and outside the cells.