bio osmolarity

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chiddler

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Vertebrates have developed various renal structures for osmoregulation based on their habitats. Bony fish that live in seawater drink large amounts of seawater and use cells in gills to pump excess salt out of the body. This is in response to:

A. a loss of water by active transport to their hypertonic surroundings.
B. a loss of salt to their surroundings.
C. an influx of water by osmosis into their tissues.
D. a need to maintain their tissues in a hypertonic state.






Answer is D.

Explanation: "Different organisms have different needs to maintain their water balance, depending on the environment they live in. Bony fish living in saltwater maintain hypoosmotic body fluids. The hyperosmotic water they live in tends to draw water out of their body by osmosis. They can obtain water by ingesting ocean water, but this raises their internal osmolarity. They excrete salt, then, to lower their internal osmolarity."


First, I look at the question: they consume large amounts of seawater and spit out salt. This means that they maintain hypoosmotic conditions. Water moves out by osmosis, and they drink + desalinate to maintain osmolarity.

So they try to keep their tissue in a HYPOosmotic state, right? Not a hyperosmotic. I don't understand why D is correct. Actually I don't find any of the answers satisfactory...

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yeah it's def a tricky one! I thought of it this way that the tissue needs to be hypertonic to their circulation so it can draw water in... vs. if the tissue is hypotonic, water leaves the cells.... but the circulation ends up being hypoosmotic to the environment cuz they need the water and not the salt... so it's pumped out!

yeah still not too satisfactory I think!

EDIT: come to think of it.... what I just said is kinda like C so nvrmind... is this TBR/Kaplan/etc?!
 
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yeah it's def a tricky one! I thought of it this way that the tissue needs to be hypertonic to their circulation so it can draw water in... vs. if the tissue is hypotonic, water leaves the cells.... but the circulation ends up being hypoosmotic to the environment cuz they need the water and not the salt... so it's pumped out!

yeah still not too satisfactory I think!

EDIT: come to think of it.... what I just said is kinda like C so nvrmind... is this TBR/Kaplan/etc?!

Question is from here.

I didn't distinguish between body fluids and body tissue :x. Realized after reading your response. So the tissue must be hyperosmotic to the body fluids. The desalination is to keep the body fluids hypoosmotic so that water can enter the tissue as needed.

When you write "so it's pumped out", the salt is pumped out! Not water. So this is starting to make more sense.
 
yeah that's what I mean, I just wish it was worded differently... cuz it sounds like fish pumps out the salt and it gets hypertonic... but I think that's the distinction they are trying to make from body fluids to tissue!
 
yeah that's what I mean, I just wish it was worded differently... cuz it sounds like fish pumps out the salt and it gets hypertonic... but I think that's the distinction they are trying to make from body fluids to tissue!

thank you
 
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