Use the diagram below to answer the question.
Structure of a Nephron
Modified from image courtesy of NIH
The human kidney contains approximately one million nephrons. The diagram shows the structure of one such nephron. As the functional unit of the kidney, a nephron is responsible for removing wastes and excess water from the blood. The nephron also has the ability to conserve nutrients, salt, and water as needed and return them to the blood supply. How do the unique structures of the tubules in a nephron most likely help the kidney perform its function?
A.
They allow the nephron to filter and absorb various substances.
B.
They permit fluids inside the kidney to reverse flow direction when needed.
C.
They enable the kidney to trap pathogens that could enter the bloodstream.
D.
They decrease the amount of time fluids are inside the kidney.