In which of the following organisms would there be the greatest need for osmoregulation?

• A. An amphibian living in a moist environment
• B. A terrestrial insect
• C. A freshwater fish
• D. A marine bony fish

Answer: (D)

Verified step by step guidance

1. Understand the concept of osmoregulation: Osmoregulation is the process by which organisms maintain the balance of water and solutes in their bodies to ensure proper cellular function. Different environments pose unique challenges for osmoregulation.
2. Analyze the marine bony fish's environment: Marine bony fish live in saltwater, which has a higher concentration of solutes (like salt) than the fish's internal body fluids. This creates a situation where water tends to move out of the fish's body via osmosis, and solutes tend to move in.
3. Identify the osmoregulatory challenge for marine bony fish: To counteract water loss and prevent excessive salt accumulation, marine bony fish must actively regulate their internal environment. They do this by drinking seawater, excreting excess salts through specialized cells in their gills, and producing small amounts of concentrated urine.
4. Compare the osmoregulatory needs of other organisms: Amphibians in moist environments face minimal osmoregulatory challenges because their surroundings are similar to their internal conditions. Terrestrial insects have adaptations to minimize water loss, but their osmoregulatory needs are less intense than those of marine bony fish. Freshwater fish face the opposite challenge of marine fish, as water tends to enter their bodies, but their osmoregulatory mechanisms are less demanding than those of marine fish.
5. Conclude why marine bony fish have the greatest need for osmoregulation: The marine environment's high salinity creates significant osmotic stress, requiring marine bony fish to have highly specialized and energy-intensive osmoregulatory mechanisms to survive.