Final answer:
Hyperosmotic urine helps the body combat water loss by conserving water, while hyposmotic urine combats water gain by excreting excess water. The kidney's role in maintaining osmotic balance involves regulating water following Na+, not K+, and the function of ADH in varying the water reabsorption.
Step-by-step explanation:
The correct phrase to complete the student's question is Hyperosmotic urine combats water loss, and Hyposmotic urine combats water gain. Hyperosmotic urine is more concentrated and is produced when the body needs to conserve water, such as in dehydration conditions. This is due to the release of antidiuretic hormone (ADH), which increases water reabsorption in the kidneys, resulting in a smaller volume of more concentrated urine. Conversely, when there is excess water in the body, the kidneys produce hyperosmotic urine, which is less concentrated and has a larger volume, to eliminate the surplus water and maintain osmotic balance.
Water follows Na+ (sodium ions) in the body, not K+ (potassium ions), to regulate urine concentration. While water balance and electrolyte balance are key in maintaining proper renal function and systemic blood pressure, it is primarily the sodium ions that lead to water reabsorption in the kidneys.
Thus, the complete and correct sentence would be: Hyperosmotic urine combats water loss, and Hypoosmotic urine combats water gain. The choices provided that water follows K+ to make urine and that osmotic balance is maintained between waste matter and bodily fluids, the more accurate statement in this context would be related to the latter, as the osmotic balance is indeed maintained between bodily fluids; however, it is the Na+ ions that play a more significant role than K+ ions in this process.