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.

"menstrual cycle is a complex cycle that consists of several processes. order of occurrence of steps in menstrual cycle are as follows:

1. high progesterone levels maintain the endometrium lining of the uterus.

2. endometrium lining breaks down and low levels of estrogen stimulate the pituitary to release fsh and lh.

3. fsh and lh stimulates the follicles to develop and the oocyte to produce estrogen.

4. rising estrogen levels suppress fsh production and development of other follicles.

5. a spike in lh causes follicle to rupture.

6. a breakdown of corpus luteum causes progesterone level to drop."