Question

Salmon regulates its internal water and salt concentrations during its swimming in the ocean and migrates to fresh water to spawn, is described by

• A. In salt water, the salmon loses water by osmosis; it drinks salt water and disposes of excess salt through its gills. In fresh water, the salmon gains water by osmosis; its kidneys excrete large quantities of urine along with some salts, and it replenishes the lost salts through uptake by its gills and digestive system
• B. In salt water, the salmon gains water by osmosis; it drinks salt water and disposes of excess salt through its gills. In fresh water, the salmon loses water by osmosis; its kidneys excrete large quantities of urine along with some salts, and it replenishes the lost salts through uptake by its gills and digestive system
• C. In salt water, the salmon loses water by osmosis; it drinks salt water and stores excess salt in its body cavity. In fresh water, the salmon gains water by osmosis; its kidneys excrete large quantities of urine and salts
• D. In salt water, the salmon gains water by osmosis; it drinks salt water and stores excess salt in its body cavity. In fresh water, the salmon loses water by osmosis; its kidneys excrete large quantities of urine and salt
• E. In salt water, the salmon gains water by osmosis and loses salt by diffusion. In fresh water, the salmon loses water by osmosis and gains salt through diffusion

Answer 1

The correct option is A In salt water, the salmon loses water by osmosis; it drinks salt water and disposes of excess salt through its gills. In fresh water, the salmon gains water by osmosis; its kidneys excrete large quantities of urine along with some salts, and it replenishes the lost salts through uptake by its gills and digestive system

In salt water, the salmon loses water by osmosis; it drinks salt water and disposes of excess salt through its gills. In fresh water, the salmon gains water by osmosis; its kidneys excrete large quantities of urine along with some salts, and it replenishes the lost salts through uptake by its gills and digestive system.

Salmon spend most of their life in the open ocean, where they reach sexual maturity, but lay their eggs gravel beds at the upper reaches of (freshwater) streams. When the eggs hatch, the young salmon spend several months migrating downstream to the ocean where they remain for some 3-5 years. When mature, the adult salmon return to mouth of stream where they hatched (they remember the taste/smell of the water in the stream), migrate upstream to its headwaters, spawn, and die.

Salmon adjust from fresh water to salt water, and back again by the method of Osmoregulation - That is, the control of body fluids and ions during the transition from fresh water to salt water and back again. This is an important transition in the life of every Pacific salmon.

To offset the dehydrating effects of salt water, the salmon drinks copiously (several liters per day). But in fresh water (where water loading is the problem) the salmon doesn't drink at all. The only water it consumes is that which necessarily goes down its gullet when it feeds. Of course, when an ocean-dwelling salmon drinks, it takes in a lot of NaCl, which exacerbates the salt-loading problem.

Kidney function also differs between the two habitats. In fresh water, the salmon's kidneys produce large volumes of dilute urine (to cope with all of the water that's diffusing into the salmon's body fluids), while in the ocean environment, the kidneys' urine production rates drop dramatically and the urine is as concentrated as the kidneys can make it. The result of this is that the salmon is using relatively little water to get rid of all of the excess ions it can (due to structural and functional limitations, the salmon's kidney cannot make its urine anywhere near as concentrated as humans can, but they do their best).