Osmolarity Ionic concentrations (mM) Habitat (mosM)N+ Ca2+ Mg2+SO 10 10.2 Seawat

Question

Osmolarity Ionic concentrations (mM) Habitat (mosM)N+ Ca2+ Mg2+SO 10 10.2 Seawatert 1000 460 10 53 540 oelenterata Aurelia (jellyfish) SW 454 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 below Aurelia is an osmoconformer Aurelia is an ionoconformer

Explanation / Answer

1. From the osmolarity calculation of the sea water, it is concluded that Na and Cl contribute more than the other ions.

Osmolarity of seawater = concentration of [Na++ Cl-] = 460 + 540 =1000

So osmolarity of extra cellular jelly fish = 454+554 = 1008

2. Greater than calculated pressure.

For ideal solution pi = RT (n/V)

For non ideal, pi = cRT (n/V)

3. Osmoconformer. Since osmolarity of extra cellular fluid = osmolarity of surrounding (sea water).

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