Osmosis isotonic solutions

Osmotic pressure plays an important role in biological chemistry because the cells of the human body are encased in semipermeable membranes and bathed in body fluids. Under normal physiological conditions, the body fluid outside the cells has the same total solute molarity as the fluid inside the cells, and there is no net osmosis across cell membranes. Solutions with the same solute molarity are called isotonic solutions. 

Osmosis, water movement across a semipermeable membrane driven by differences in osmotic pressure, is an important factor in the life of most cells. Plasma membranes are more permeable to water than to most other small molecules, ions, and macromolecules. This permeability is due partly to simple diffusion of water through the lipid bilayer and partly to protein channels (aquaporins see Fig. 11-XX) in the membrane that selectively permit the passage of water. Solutions of equal osmolarity are said to be isotonic. Surrounded by an isotonic solution, a cell neither gains nor loses water (Fig. 2-13). In a hypertonic solution, one with higher... 

Osmosis also has consequences for laboratory protocols. Mitochondria, chloroplasts, and lysosomes, for example, are bounded by semipermeable membranes. In isolating these organelles from broken cells, biochemists must perform the fractionations in isotonic solutions (see Fig. 1-8). Buffers used in cellular fractionations commonly contain sufficient concentrations (about 0.2 m) of sucrose or some other inert solute to protect the organelles from osmotic lysis. 

Osmosis plays a significant role in the function of organisms. A cell that is immersed in pure water undergoes plasmolysis. The cell wall permits water to flow into it thereupon the cell becomes distended, the wall stretches until it ultimately ruptures or becomes leaky enough to allow the solutes in the cellular material to escape from the interior. On the other hand, if the cell is immersed in a concentrated solution of salt, the water from the cell flows into the more concentrated salt solution and the cell shrinks. A salt solution which is just concentrated enough so that the cell neither shrinks nor is distended is called an isotonic solution. 

A 0.90% (0.15 M) sodium chloride solution is known as a physiological saline solution because it is isotonic with blood plasma that is, it has the same concentration of NaCl as blood plasma. Because each mole of NaCl yields about 2 mol of ions when in solution, the solute particle concentration in physiological saline solution is nearly 0.30 M. Five-percent-glucose solution (0.28 M) is also approximately isotonic with blood plasma. Blood cells neither swell nor shrink in an isotonic solution. The cells described in the preceding paragraph swell in water because water is hypotonic to cell plasma. The cells shrink in 5%-urea solution because the urea solution is hypertonic to the cell plasma. To prevent possible injury to blood cells by osmosis, fluids for intravenous use are usually made up at approximately isotonic concentration. 

Because the cell membranes in biological systems are semipermeable, osmosis is an ongoing process. The solutes in body solutions such as blood, tissue fluids, lymph, and plasma all exert osmotic pressure. Most intravenous (FV) solutions used in a hospital are isotonic solutions, which exert the same osmotic pressure as body fluids such as blood. The percent concentration typically used in IV solutions is similar to the types of percent concentrations we have already discussed, except that the concentration of IV solutions is mass/volume percent m/v). The most typical isotonic solutions are 0.9% (m/v)... 

The particles in a solution lower the freezing point, raise the boiling point, and increase the osmotic pressure. In osmosis, solvent (water) passes through a semipermeable membrane from a solution with a lower osmotic pressure (lower solute concentration) to a solution with a higher osmotic pressure (higher solute concentration). Isotonic solutions have osmotic pressures equal to that of body fluids. 

Because the cell membranes in biological systems are semipermeable, osmosis is an ongoing process. The solutes in body solutions such as blood, tissue fluids, lymph, and plasma all exert osmotic pressure. Most intravenous (IV) solutions used in a hospital are isotonic solutions,... 

As you doubtlessly learned in physiology, osmosis is diffusion of water through a semipermeable membrane. The semipermeable membrane allows water to move through it, but most solute particles are either too big or too polar to make it across the membrane. The relative concentration of solutes in osmotic systems is called the tonicity. Two solutions are isotonic if they contain equal concentrations of particles. If the concentrations are not equal, the one with the greater concentration is the hypertonic solution, and the one with the lower concentration is the hypotonic solution. It is critically important to notice that tonicity is a comparative concept, and it makes no sense to call a solution hypertonic without indicating to which solution you are comparing it. For example, is a 5% NaCl solution hypotonic or hypertonic You are probably tempted to say hypertonic, because you are mentally comparing this solution to normal saline, which is 0.89% (w/w) NaCl. So, 5% NaCl is hypertonic to normal saline. However, 5% NaCl is hypotonic to 10% NaCl and isotonic with another solution of 5% NaCl. 

Mammalian red blood cells have a biconcave (doughnut-like) shape. If red blood cells are placed in a 0.3 M NaCl solution, there is little net osmotic movement of water, the size and shape of the cells stay the same the NaCl solution is isotonic to the cell. If red blood cells are placed in a solution with a lower solute concentration than is found in the cells, water moves into the cells by osmosis, causing the cells to swell such a solution is hypotonic to the cells. When red blood cells are placed in pure water, water rapidly enters the cells by osmosis and causes the cells to burst, a phenomenon known as hemolysis. If the red blood cells are placed in a solution with a higher solute concentration, water moves out of the cell by osmosis, the cell becomes smaller and crenated in shape such a solution is hypertonic to the cells. 

Blood plasma has an osmolarity equivalent to a 0.30 M glucose solution or a 0.15 M NaCl solution. This latter is true because in solution NaCl dissociates into Na+ and Cl and thus contributes twice the number of solute particles as a molecule that does not ionize. If red blood cells, which have an osmolarity equal to blood plasma, are placed in a 0.30 M glucose solution, no net osmosis will occur because the osmolarity and water concentration inside the red blood cell are equal to those of the 0.30 M glucose solution. The solutions inside and outside the red blood cell are said to be isotonic iso means "same," and tonic means "strength") solutions. Because the osmolarity is the same inside and outside, the red blood cell will remain the same size (Figure 18.20b). 

Consider the following problem. A spherical cell consists of a thin membrane surrounding a salt solution. Outside of the cell membrane there is a solution that is isotonic with that within the membrane. The cell is removed instantaneously from its surroundings and placed into an environment of piue water. The action of osmosis immediately drives water through the... 

Osmosis is the passage of a solvent (usually water) from a zone of low concentration to one of high concentration. The solution of higher concentration is said to be hypertonic ( hyper- means more), whereas the solution of lower concentration is said to be hypotonic ( hypo- means less). After osmosis is complete, the solutions are equally concentrated and are said to be isotonic ( iso- means the same). An example of osmosis is shown in Fig. 11.10. 

If two solutions of identical osmotic pressure are separated by a semipermeable membrane, no osmosis will occur. The two solutions are isotonic with respect to each other. If one solution is of lower osmotic pressure, it is hypotonic with respect to the more concentrated solution. The more concentrated solution is hypertonic with respect to the dilute solution. 

Osmosis plays an important role in living systems. The membranes of red blood cells, for example, are semipermeable. Placing a red blood cell in a solution that is hypertonic relative to the intracellular solution (the solution inside the cells) causes water to move out of the cell ( FIGURE 13.26). This causes the cell to shrivel, a process called crenation. Placing the cell in a solution that is hypotonic relative to the intracellular fluid causes water to move into the cell. This may cause the cell to rupture, a process called hemolysis. People who need body fluids or nutrients replaced but cannot be fed orally are given solutions by intravenous (IV) infusion, which feeds nutrients directly into the veins. To prevent crenation or hemolysis of red blood cells, the IV solutions must be isotonic with the intracellular fluids of the blood cells. 

If a red blood cell is placed in a solution that is not isotonic, the differences in osmotic pressure inside and outside the cell can drastically alter the volume of the cell. When a red blood cell is placed in a hypotonic solution, which has a lower solute concentration hypo means lower than ), water flows into the cell by osmosis. The increase in fluid causes the cell to swell and possibly burst—a process called hemolysis (see Figure 12.11b). A similar process occurs when you place dehydrated food, such as raisins or dried fruit, in water. The water enters the cells, and the food becomes plump and smooth. 

Hypotonic, 561 Ideal solution, 555 Ion pair, 559 Isotonic, 558 Miscible, 544 Molahty (m), 547 Nonvolatile, 553 Osmosis, 557... 

Some of the best examples of osmosis are those associated with living organisms. For instance, if red blood cells are placed in pure water, the cells expand and eventually burst as a result of water that enters through osmosis. The osmotic pressure associated with the fluid inside the cell is equivalent to that of 0.92% (mass/volume) NaCl(aq). Thus, if cells are placed in a sodium chloride (saline) solution of this concentration, there is no net flow of water through the cell membrane, and the cell remains stable. Such a solution is said to be isotonic. If cells are placed in a solution with a concentration greater than 0.92% NaCl, water flows out of the cells, and the cells shrink. Such a solution is said to be hypertonic. If the NaCl concentration is less than 0.92%, the solution is hypotonic, and water flow s into the cells. Fluids that are intravenously injected into patients to combat dehydration or to supply nutrients must be adjusted so that they are isotonic with blood. The osmotic pressure of the fluids must be the same as that of 0.92% (mass/volume) NaCl. 

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