transport of substances though the membrane diffusion ... · transport of substances though the...
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Transport of substances though the membrane
Diffusion, Osmosis,
and Tonicity
Lab.2
2nd stage
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OBJECTIVES
1. Distinguish between the terms solute, solvent,
and solution.
2. Define the terms passive transport, diffusion, and
active transport.
3. Define the terms osmosis, osmotic pressure, and
osmolality.
4. Define the terms isotonic, hypotonic, and
hypertonic.
5. Describe how red blood cells (RBCs) are affected when they
are placed in isotonic, hypotonic, and hypertonic solutions.
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KEY WORDS
• Solvent: (relatively large amount
the dissolving medium; in the body
Solute: (relatively small amount of
of a substance which is
is water).
a substance which is the•
dissolved substance and it dissolves in the solvent).
Solution: is a homogenous mixture of a solute in a solvent.
Concentration: of a solvent is the amount of solute
dissolved in a specific amount of solution.
•
•
• Concentration gradient: difference in the concentration of
a solute on two sides of a permeable membrane.
Equilibrium: exact balance between 2 opposing forces.
Dynamic: continuous motion or movement.
•
•
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Diffusion•The movement of molecules (or ions)from a region of their
higher concentration to a region of their lower concentration
Movement of the solutes is due to the concentration gradient
As a result
situation.
of diffusion, molecules tend to reach an equilibrium
•is a passive process, meaning that it occurs without the expenditure of
energy.
•Respiratory gases, oxygen and carbon dioxide, cross membranes by
diffusion.
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OsmosisIs a special type of diffusion involving water molecules only.
•Its defined as the movement of water molecules from a region
of their higher concentration to a region of their lower concentration
through a partially permeable membrane (which allows only certain
molecules through.
•The cytoplasm of the living cell is composed of
•water (~70% to 80% water), which is the solvent or dissolving
agent and dissolved solutes (e.g. salts, sugars, amino acids,
vitamins, etc.)
•Solvent + solute =Solution
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A molecule may move into or out of a cell by diffusion if (1) a difference in
the concentration of that molecule (concentration gradient) exists between
the intracellular and extracellular compartments, and (2) the cell membrane
will allow the passage of that molecule.
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If the solvent is water, the water will diffuse from the region where the solute/
solvent ratio is lower (relatively more water) to the region where the
solute/solvent ratio is higher (relatively less water), until the solute/solvent
ratio (concentration) is the same on both sides of the membrane. The net
diffusion of water across a membrane is called osmosis
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Tonicity
Tonicity is a description of one solution’s
compared to that of another solution.solute concentration
–
–
–
Hypertonic - more solute, less water
Hypotonic - less solute, more water
Isotonic - equal solute, equal water
erwat
hypotonic hypertonic
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In this part of the experiment, three a mount of human
blood will be made using the unknown
F.
solution .D, E,
•One is hypotonic (distilled water),
•One is hypertonic (30% NaCl), and
•Another is isotonic (0.9% NaCl)
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Principle
• The responses of RBCs to solutions of different
osmotic activities are examined under microscop.
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Procedure:
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D
Unknown solution Identify of Solution Appearance/condit ion of cells
E
F
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Expectation of osmosis
•Normal cells (un treaded)
in RBC
•In Isotonic solution
•In hypertonic solution
•Crenation
•In hypotonic solution
•Hemolysis
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The red blood cell (RBC) has the same osmolality and
the same osmotic pressure as plasma. When a red blood cell is placed in a
hypotonic solution, it will expand or perhaps even burst (a process called
hemolysis) as a result of the influx of water, extruding its hemoglobin into the
solution. When placed in a hypertonic solution, a red blood cell will shrink (a
process called crenation, fig. 2.11) as a result of the efflux of water.
RBCs will neither expand nor shrink in an isotonic solution