Which of the following is NOT an effect of aging on the kidneys?

A) Decrease in kidney size
B) Loss of nephrons
C) Decreased response to hormonal control of urine volume
D) A marked decrease in the ability to maintain homeostasis

Aging affects the kidneys in several ways, including a decrease in size, loss of nephrons, and decreased response to hormonal control, which can impact urine volume regulation. However, while aging can lead to a reduced ability to maintain homeostasis, describing it as a "marked decrease" might overstate the typical impact of aging on this function. The kidneys generally continue to maintain homeostasis effectively, albeit less efficiently, as one ages.