Osmolarity Ionic concentrations (mM) Habitat(mosM) Nat+ Ca2+ Mg2+ CSO2 Seawatert

Question

Osmolarity Ionic concentrations (mM) Habitat(mosM) Nat+ Ca2+ Mg2+ CSO2 Seawatert Coelenterata Aurelia (jellyfish) 1000 460 10 10 53 540 SW 454 10.2 9.7 51.0 554 14.6 Given the data concerning the ionic composition of the extracellular fluid for the "jellyfish" Aurelia, make some predictions about the osmotic relations of this organism 1. Assuming the solutes listed above contribute the bulk of the osmotic pressure, and that the solutes are ideal, calculate what you expect the osmolarity of the extracellular fluid to be. Write it in the box here and in the table above. 2. If the solutes above are not ideal, will the actual osmotic pressure be (circle one) Greater than that calculated above Less than that calculated above The same as that calculated above 3. Circle all the correct statements belovw Aurelia is an osmoconkocwer Aurelia is an jonoconformer

Explanation / Answer

1.Osmolarity of a solution is calculated by the concentration of each ion in the solution. For example, NaCl of concentration 1 mol dissociates into 1 sodium and 1 chloride ion. So, it has osmolarity of 2 osms.

For the given solution, adding the concentration of each ion, we get 1093.5 mM. Considering each ion to exist independently in solution and contributing to the osmotic pressure of the solution, the osmolarity of the extracellular fluid is 1093.5 mOsm.

2. In case of ideal solution, we are considering that ions are not combining with each other. For real solutions, as the ions combine to form a molecule, osmolarity of the molecule is the number of dissociated ions that can be obtained from it, multiplied with the concentration of the molecule.

So, the actual osmotic pressure would be greater than calculated above.

3. Aurelia is both an ionoconformer and osmoconformer. It maintains the concentration of solutes inside the body more or less similar to the concentration of solute outside the body. Consequently, osmotic pressure of ions is also maintained similar to the external environment.

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