Final answer:
In amphibians, when ADH is released, it causes more aquaporins to be inserted into the cell membranes of the kidney's collecting tubules, which results in increased water reabsorption and more concentrated urine, meaning the number of aquaporins in the bladder increases.
Step-by-step explanation:
When ADH (antidiuretic hormone) is released in amphibians, it initiates a series of biological events that lead to a temporary insertion of aquaporins in the cells of the collecting tubule in the kidney. Aquaporin channels are inserted into the apical membrane of principal cells, increasing water reabsorption and thereby concentrating the urine. This process is crucial in regulating blood osmolarity, blood pressure, and urine concentration. Consequently, when ADH is released, the number of aquaporins in the bladder increases, allowing more water to be reabsorbed back into the bloodstream. As such, the correct answer to the student's question is: a. increases.