Answer:
- Fresh water fish have higher salt contents in their bodies than in their environments.
- Marine fishes have less salt in their bodies than their environment
- Terrestrial organisms have the challenge of water retention due to atmospheric contact.
Explanation:
FRESH WATER OSMOREGULATION
The salt concentration in salt water fish is higher than the concentration found in its environment (fresh water). This causes water to enter into the body of the fish through osmosis and without regulating processes, the fish is bound to swell and likely burst.To compensate for this challenge, the kidney in fresh water fish produces a large amount of urine, causing them to lose salt. To ensure too salt is not lost beyond the basic requirement, chloride cells in the gills take up ions from the water which are transported into the blood.
MARINE OSMOREGULATION
In marine fishes, the challenge opposes that of fresh water fishes since salt content in this case is lower in their blood than in their environment. To address this challenge, marine fishes lose water constantly while retaining salts to lead to a build up. The water lost, is then made up for and replenished by continual drinking of seawater. The chloride cells in marine fishes works in a manner opposing that of fresh water fish, functioning to compliment the excretion of salts by the kidney.
TERRESTRIAL OSMOREGULATION
The major challenge of osmoregulation in terrestrial organisms is water regulation in the body owing to their contact with the atmosphere.
Terrestrial organisms possess effective kidneys which enable osmoregulation. A series of processes including filtration, re-absorption and tubular secretion, enable regulation of fluids and water conservation.
Water passes out of the descending limb of the loop of Henle, leaving a more concentrated filtrate inside. Salt diffuses out from the lower, thin part of the ascending limb. In the upper, thick part of the ascending limb, salt is then actively transported into the interstitial fluid. The amount of salt in the interstitial fluid, determines how much water moves out of the descending limb i.e the saltier it gets, the more water moves out of the descending limb. This process leaves a concentrated filtrate inside, so more salt passes out. Water from the collecting ducts moves out by osmosis into this hypertonic interstitial fluid and is carried away by capillaries, achieving osmoregulation.
