Final answer:
Animals in saltwater cannot produce copious hyposmotic urine because their environment is hypertonic and requires them to conserve water and excrete concentrated urine to manage salt levels.
Step-by-step explanation:
Animals in saltwater environments must employ various osmoregulatory mechanisms to survive due to the hypertonic nature of their surroundings, which has a higher salt concentration than the fluids within their cells. To maintain homeostasis, these animals cannot produce copious hyposmotic urine, which is typically a response to living in a hypotonic environment like fresh water where the body tends to take up excess water. Instead, saltwater animals adapt by secreting excess salts through specialized adaptations such as salt glands, and by living with hyposmotic blood relative to seawater, or being isosmotic by matching their internal salt levels with their environment. Sharks, a type of cartilaginous fish, leverage organs like the rectal gland to secrete salt and assist in osmoregulation, and they maintain isotonicity with seawater through high urea concentrations and TMAO, which stabilizes proteins. Therefore, the correct answer to the student's question is that animals in saltwater cannot produce copious hyposmotic urine (option c), as their environment requires the conservation of water and the excretion of concentrated urine to manage salt levels.