Diffusion/Osmosis Notes

In Preparation for the Plankton Lab

I. Definitions: solute: a substance that gets dissolved (ex: salt) solvent: a substance in which a solute is dissolved ���(ex: water) solution: a mixture in which a solute is dissolved evenly throughout a solvent (ex: ocean water) concentration: the percent represented by either the solute or solvent In ocean water, salt is the solute, water is the solvent, and the result is a solution. Salt and water can be in a variety of concentrations which make the water more or less salty.

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diffusion: the movement of molecules in a solution from an area of higher concentration to an area of lower concentration

osmosis: the diffusion of water molecules from an area of high to low concentration semi-permeable membrane: a membrane which allows the passage of some molecules (ex. water), while preventing the passage of other substances (some molecules are prevented from passing through due to their size and/or charge) Single-celled water organisms have a semi-permeable membrane that lets water through, but salt is too large to pass through.

water

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II.  Osmosis and Cells - 3 Examples A. Hypotonic - a situation where there is a solution with a lesser concentration of solute outside the cell compared to the concentration of solute inside the cell

Ex: a single-cell salt water���organism is placed in a fresh or brackish water solution

brackish water

Since salt is too big to move through the membrane, water moves from an area of high concentration in the brackish water through the cell’s membrane, causing the cell to swell. This will continue to happen until the concentration of water inside the cell equals the concentration outside the cell - or - until the cell explodes

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B. Hypertonic – A situation where there is a solution with a greater concentration of solute outside the cell compared to the concentration of solute inside the cell

Ex: a single-cell fresh water organism is placed in a sea water solution

sea water

Since salt is too big to move, water moves from an area of high concentration in the cell through the cell’s membrane causing the cell to shrink. This will continue to happen until the concentration of water inside the cell equals the concentration outside the cell - or - until the cell collapses

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C. Isotonic – A situation where there is a solution with an equal concentration of solute outside the cell compared to the concentration of solute inside the cell

Ex: a single human red blood cell is placed in a 0.9% saline (salt) solution.

0.9% saline

Since the concentration of salt and water is the same inside and outside the cell, neither the salt nor the water has to move to balance. Water can still pass through the cell’s membrane but there is no net gain or loss of water inside the cell

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Osmosis

Animation

Osmosis Overview

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Some organisms have developed adaptations to prevent themselves from swelling or shrinking:

III. Facilitated Diffusion A. Moves molecules from a high to low concentration B. no energy required (In the direction nature intends) C. molecules called carrier proteins imbedded in the cell membrane facilitate the movement D. Organisms now can move salt in or out of their cells to balance themselves instead of being flooded/emptied of water E. Ex: Red blood cells carry and deliver glucose into the bloodstream

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IV. Active Transport A. Moves molecules from an area of lower concentration to an area of higher concentration (the opposite direction than nature intends) B. an adaptation requiring both carrier proteins and energy C. carrier proteins and high energy molecules pump molecules from low to high concentration D. Ex: the gills of marine fish have cells that remove salt from the body and pump it back into the water

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