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5 Cards in this Set
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Osmolarity -- measure of solutes in solution.
[Osm] sea water > [Osm] freshwater = sea water contains lots of NaCl. |
Passive diffusion of water (osmosis) from low osmolarity to high osmolarity --> until equilibrium (i.e. equal osmolarity on both sides of membrane).
Dep. on how permeable membrane is, solutes (if small enough) might passively diffuse across too. |
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Water only moves via osmosis. Animals can actively pump solutes across a membrane to make water move in the intended direction.
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[Osm] of sea water can vary:
i.e. Meditteranean has high salt content because semi-enclosed, high temps (= high evaporation) and low freshwater input. i.e. Hudson Bay = low salt content because low temps (= low evaporation), high input of freshwater, semi-enclosed (reduced input from sea). |
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Common Jelly (Aurelia):
ECF is osmoconforming and ionoconforming, therefore same as sea water. Saves energy (i.e. no pumping of ions). Stenohaline: cannot withstand big fluctuations in salinity. If moves into different environment = water flows into body and dies! |
Vast majority of marine inverts = stenohaline & conforming.
Not fullproof: as organism is alive --> contains non-diffusable solutes of body --> [Osm] slightly higher in body, thus water slowly moves into body. Solution: have a few pumps to actively pump ions out of body to create efflux of water from body. This is the DONNAN EFFECT. |
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Differences:
Sea has 470 arbitrary units (au) Na, 550 au Cl and osmotic potential (or osmolarity, OP) of 1100. ECM as 470 au Na, 550 au Cl and 1100 OP. Cytoplasm has 70 au Na, 100 au Cl and 1100 OP. Hence, ECM = osmo- & iono-conforming and cytoplasm = osmoconformer and ionoregulator. |
Donnan effect --> some pumps --> ECM & seawater have same [Osm] = kept at equilibrium.
Cell is hyporegulated (i.e. ions kept at lower levels inside than outside) because Na & Cl ions are cytotoxic. |
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K ions are hyperregulated = not cytotoxic --> keeps OP constant.
This requires many active pumps on cell membrane because: K ions have a natural tendency to passively efflux into ECM from cell. Na and Cl ions have a natural tendency to passively influx into cell from the ECM. Requires lots of pumps to maintain the OP. |
How do marine inverts cope with sea water?
Reduced skin permeability -- prevent constant movement of ions. Ca, Mg, SO4 ion (heavy divalents) concentrations are regulated (crustaceans need Ca ions during ecdysis or moulting for their shells; and pelagic molluscs hyperregulate for buoyancy). Symport pumps pump ions in same direction and antiport pumps pump ions in opposite directions. Stenohaline inverts use body surface for salt loss/uptake. Some use simple organs i.e. nephridia. |
