Transport of substances though the membrane

Diffusion, Osmosis,

and Tonicity

Lab.2

2nd stage

Zhikal.omer@tiu.edu.iq

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.

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.

•

•

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.

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

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.

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

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

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)

Principle

• The responses of RBCs to solutions of different

osmotic activities are examined under microscop.

Procedure:

D

Unknown solution Identify of Solution Appearance/condit ion of cells

E

F

Expectation of osmosis

•Normal cells (un treaded)

in RBC

•In Isotonic solution

•In hypertonic solution

•Crenation

•In hypotonic solution

•Hemolysis

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