Salmon eggs hatch in fresh water. the fish then migrate to the ocean (a hypertonic solution) and, after several years of feeding and growing, return to fresh water to breed. how can these organisms make the transition from fresh water to ocean water and back to fresh water?
a. salmon in fresh water excrete concentrated urine, and salmon in salt water secrete dilute urine.
b. the rectal gland functions in the ocean water, and chloride cells function in fresh water.
c. the salt transport mechanisms of the gill epithelia change during migration.
d. their metabolism changes in salt water to degrade electrolytes.

Letter C

Explanation:

Salmon have a physiological adaptation that allows osmoregulation to occur in two different environments (seawater and freshwater). There are specific molecules in the salmon gills that "pump" and "remove" Na and Cl ions. When at sea these molecules pump the ions out of the salmon's body and into freshwater, the same molecules remove Na and Cl from the water bringing it into the animal's blood.

his research revealed two genetically different groups of prokaryotes, which justified splitting kingdom monera into two kingdoms. the genetic and cellular differences were so great, that these two kingdoms were eventually placed into different domains in the current three-domain system.

"d.) carbon dioxide and hydrogen sulfide"