Sample Questions for Exam #2

Animal Physiology - Biology 345

1) A typical animal cell is pictured below; the steady state concentrations of ions inside and outside the cell are given.  The measured membrane voltage, Vm, is -68 mV.  Calculate the Nernst potential, Ej, for each ion (all ions are permeable).  Based upon your calculations, the observed steady-state concentrations and the Vm, determine if each ion is or is not in equilibrium.  Then determine if the ion will move in, out or neither in response to its electrochemical gradient.  Finally, determine if the cell must transport the ion in or out to maintain the steady state, or if the ion is distributed passively (i.e. in equilibrium).
 


 
 

Show your calculations.

2) In sea water ( [Na+]=450mM, [Cl-]=500mM, 1000mOsm), the blue crab, Callinectes, has a hemolymph concentration equal to that of the medium. If the crab is abruptly transferred to 10% sea water, the hemolymph concentration falls to  ( [Na+] = 180mM, [Cl-] = 200mM, 400mOsm).

What would the swelling pressure of the crab’s cells be if the animal were unable to compensate for the change in osmolarity? (R= 0.082 liters • atm • ?K-1 • mol-1 and T= 300 ?K)

What cell volume regulatory mechanisms might come into play to protect the crab’s cells from this intolerable swelling pressure?

3) Briefly describe the osmotic and ionic problems encountered by a marine teleost (bony fish).  What adaptations have evolved to allow the fish to compensate for these problems?

Suppose that you hooked this fish on a line, and it escaped after a long, hard fight.  Both you and the fish have accumulated lactic acid, resulting in metabolic acidosis.  Why do you and the fish have different mechanisms to re-establish acid/base balance, and what are they?

4) After fighting the fish, you are very dehydrated because you sweated profusely.  Your blood NaCl concentration is low and your blood volume (and therefore blood pressure) is low.  What hormonal regulatory mechanisms will come into play and how do they act on the kidney to help you restore salt and water balance?

return to Bio 345 Syllabus

revised 02 October 2000