Osmotic Balance in a Marine Frog The crab-eating frog of Southeast Asia, Rana ca

Question

Osmotic Balance in a Marine Frog The crab-eating frog of Southeast Asia, Rana cancrivora, develops and ma- tures in fresh water but searches for its food in coastal man- grove swamps (composed of 80% to full-strength seawater). When the frog moves from its freshwater home to seawater it experiences a large change in the osmolarity of its envi- ronment (from hypotonic to hypertonic).

(a) Eighty percent seawater contains 460 mM NaCl, 10 mM KCl, 10 mM CaCl2, and 50 mM MgCl2. What are the con- centrations of the various ionic species in this seawater? As- suming that these salts account for nearly all the solutes in seawater, calculate the osmolarity of the seawater.

(c) Like all frogs, the crab-eating frog can exchange gases through its permeable skin, allowing it to stay under- water for long periods of time without breathing. How does the high permeability of frog skin affect the frog

Explanation / Answer

c. the cells will shrink in size , when moving from fresh water environment to sea water environment . or can say from hypotonic solution to hypertonic solution .

a. to calculate the osmolarity of sea water , we will convert the values in osmoles/litre and add them all , 460mM NaCl + 10 mM CaCl2 +10 mM KCl + 50 mM MgCl2 = 500 mosmoles / litre .

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