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Hypertonic vs. hypotonic
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Kaylene_5146
#1 Posted : Saturday, July 10, 2021 12:16:45 AM
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On the MCAT when talking about hyper and hypotonic are we talking about the concentration of water or the concentration of solute relative to it's environment?

-The textbook (Biology 2 p. 28) says if the cell is hypotonic to it's environment, water will exit the cell, and it will shrivel, but I thought that hypotonic would have solute enter and the cell burst?

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INSTR_Molly_129
#2 Posted : Saturday, July 10, 2021 12:37:21 AM
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Hello Kaylene,

Tonicity refers to the concentration of solutes. So when something is hypotonic, it means that it is low in concentration in comparison to another source of concentration.

Therefore, when a cell is hypotonic to its environment, it has a lower concentration of ions inside the cell, than outside. Therefore, water will rush in to attempt to bring the concentration to an equilibrium.

Hope that helps, happy studying!

Molly
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Kaylene_5146
#3 Posted : Saturday, July 10, 2021 1:06:24 AM
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Hi, thank you for the explanation. If water is rushing into the cell wouldn't that mean that the cell would burst then (not shrivel as it says on p. 28)?
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INSTR_Molly_129
#4 Posted : Saturday, July 10, 2021 2:16:42 AM
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Oops, I made a typo and switched in with out. To clarify:

- Hypotonic = low concentration of ions in cell in comparison to solution. Water will rush OUT of the cell and the cell will shrivel. For example, [Cell] = 500 mM, [Solution] = 1000 mM. Water will rush out of the cell to get to [Cell] = 750 mM and [Solution] = 750 mM.
- Hypertonic = high concentration of ions in comparison to solution. Water will rush IN to the cell, and cell will burst. For example, [Cell] = 500 mM, [Solution] = 300 mM. Water will rush into the cell to get to [Cell] = 400 mM, and [Solution] = 400 mM.

Hope that clears everything up!

Cheers,

Molly
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