Osmosis

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  • Created by: Lotto65
  • Created on: 19-11-16 14:29
What are plasma membranes freely permeable to?
Water
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Why is the passive movement of water across membranes different to diffusion across membranes?
Water is the solvent
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What determines the movement of water across a membrane?
The concentration of solutes
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What is osmosis?
The passive movement of water molecules from a region of high to low concentration across a partially permeable membrane
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What causes water molecules to physically move?
The attractions between the solutes and water molecules
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Why does water move instead of the solutes diffusing out?
The membrane is impermeable to them
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Why is the net movement from high to low water concentration?
Water moves in both directions but more moves from high to low than low to high - IM forces between solutes and water molecules restricts water molecule movement so in a higher solute concentration, less water can move freely
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What is osmolarity?
The number of moles of solute per unit volume of solution
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What is the osmolarity of pure water?
0
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The greater the concentration of solutes...
The greater the osmolarity
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What direction does water move in terms of osmolarity?
Low to high osmolarity - if they are in equal pressure and separated by a partially permeable membrane
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Hypotonic solutions have what osmolarity?
Low
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Hypertonic solutions have what osmolarity?
High
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How do you work out the percentage mass change?
(final mass - initial mass)/ initial mass x100
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Why does glucose have an equal molarity and osmolarity?
Glucose remains as single molecules when it reacts
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What is the osmolarity of sodium chloride solution related to its molarity?
Double the molarity
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Why is sodium chloride solution's osmolarity double its molarity?
It has two moles of ions - one of sodium and one of chlorine
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How do you know when you have found the solution isotonic to the plant cells?
No mass change
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Give two ways of making osmolarity experiments accurate?
Meausure volumes with a volumetric flask; Use the same electronic balance that is accurate to 0.01g
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Why must human tissues or organs be bathed in a solution that is the same osmolarity as cytoplasm?
Osmosis could occur if not which would cause cells to burst and swell or shrink
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How do they prevent damaging tissues or organs by osmosis for transplants?
Put them in an isotonic saline (solution of salts); Surrounded by isotonic slush which includes low temperatures to keep them in a healthy state
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How do substances dissolve in water? What does this do to water molecules?
Form intermolecular bonds with water molecules - restricts movement of water molecules
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Why can osmosis happen in all cells?
Water molecules are small enough to fit through the phospholipid bilayer
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What are aquaporins?
Water channels in some membranes to increase the permeability of water
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Give examples of cells with aquaporins in their membranes
Kidney cells reabsorb water; Root hair cells
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Why are H+ ions prevented from going through the aquaporin?
The middle of the channel is only just wider than a water molecule so they pass through single file. Positive charges prevent protons passing through (H+) at this point
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An isotonic solution has the same... as the solution
Osmolarity
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What are crenellations?
Indents in the plasma membrane of the cell if water leaves the cell, as the plasma membrane does not change volume but the cytoplasm shrinks
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What salt is used in an isotonic saline?
Sodium chloride
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Give some uses of salines
Introduced to patient's blood system via a drip; Used to rinse wounds or abrasions; Used to keep damaged areas of skin moist before a skin graft; basis for eye drops; Organ/ tissue donation
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Other cards in this set

Card 2

Front

Why is the passive movement of water across membranes different to diffusion across membranes?

Back

Water is the solvent

Card 3

Front

What determines the movement of water across a membrane?

Back

Preview of the front of card 3

Card 4

Front

What is osmosis?

Back

Preview of the front of card 4

Card 5

Front

What causes water molecules to physically move?

Back

Preview of the front of card 5
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