Biological systems, osmotic pressure

For determination of the molar mass of an unknown compound, a measured mass of material is dissolved to give a measured volume of solution. The system is held at constant temperature, and the osmotic pressure is determined. Osmotic pressure measurements are particularly useful for determining the molar masses of large molecules such as pol3TTiers and biological materials, as Example illustrates. 

Osmose plays an essential role in a wide technological and especially in biological systems represented by solutions of biopolymers. That is why understandable is interest of scientists to the problem of osmotic pressure of polymeric solutions which permits comparatively easy experimentally to determine the advantages and deficiencies of theoretical imaginations about thermodynamical properties of polymeric solutions. 

In the meantime, the intense study of the simpler vesicle systems has unravelled novel, unsuspected physicochemical aspects - for example growth, fusion and fission, the matrix effect, self-reproduction, the effect of osmotic pressure, competition, encapsulation of enzymes, and complex biochemical reactions, as will be seen in the next chapter. Of course the fact that vesicles are viewed under the perspective of biological cell models renders these findings of great interest. In particular, one tends immediately to ask the question, whether and to what extent they might be relevant for the origin of life and the development of the early cells. In fact, the basic studies outlined in this chapter can be seen as the prelude to the use of vesicles as cell models, an aspect that we will considered in more detail in the next chapter. 

Why are isotonic drinks useful Osmotic pressure in living systems is incredibly important yet how often is the topic dismissed or merely discussed as a means to measure molecular weight of polymers Why not consider polymers as biological macromolecules and add to the discussion that a balance of osmotic pressure keeps our cells from bursting - which goes back to why the isotonic sport drinks are useful Relevance in the examples used in our courses is possible. 

In biological systems with dilute aqueous solutions, the last term in Eq. (10.3) disappears, since zw = 0 and the activity of the species determines the osmotic pressure (II). For water, we have... 

Osmotic pressure is extremely important in biological systems. For example, in trees, it helps in moving liquids from the root systems to the tops. Water returns from human tissue to blood capillaries because of the greater concentration of solutes in the blood. The use of saline solution when replacing blood in accident victims must be carefully controlled so that the fluid s osmotic pressure is the same as that of blood. 

Osmotic pressure is another property due to dissolved substances. The presence of solute particles lowers the ability of solvent molecules to pass through a semipermeable membrane. Osmotic pressure is very important in biological systems, and an application of the theory behind osmotic pressure allows for the purification of seawater. The osmotic pressure of a solution, IT, is proportional to the molarity (the number of moles per liter) ... 

Osmometry is a technique for measuring the concentration of solute particles that contribute to the osmotic pressure of a solution. Osmotic pressure governs the movement of solvent (water in biological systems) across membranes that separate two solutions. Different membranes vary in pore size and thus in their ability to select molecules of different size and shape. Examples of biologically important selective membranes are those enclosing the glomerular and capillary vessels that are permeable to water and to essentially aU small molecules and ions, but not to large protein molecules. Differences in the concentrations of osmoticaUy active molecules that carmot cross a membrane cause those molecules that can cross the membrane to move to establish an osmotic equilibrium. This movement of solute and permeable ions exerts what is known as osmotic pressure. 

Water molecules are constantly in motion, even in ice. In fact, the translational and rotational mobility of water directly determines its availability. Water mobility can be measured by a number of physical methods, including NMR, dielectric relaxation, ESR, and thermal analysis (Chinachoti, 1993). The mobility of water molecules in biological systems may play an important role in a biochemical reaction s equilibrium and kinetics, formation and preservation of chemical gradients and osmotic pressure, and macromolecular conformation. In food systems, the mobility of water may influence the engineering processes — such as freezing, drying, and concentrating chemical and microbial activities, and textural attributes (Ruan and Chen, 1998). 

Microbial activity is a major concern in systems in which water-based fluids are used. Particularly, glycol fluids provide a good source of nutrition to some types of biological species. In salt-based brines, however, microbes do not survive because of high osmotic pressure. When microbes start to grow inside a system, they create a layer known as biofilm on the walls of the pipes and heat exchangers. This reduces the heat transfer rate. Some microbes are capable of creating acids and hence cause a substantial amount of corrosion in the system. 

A buffer solution is a solution of(l)a weak acid or a weak base and (2) its salt both components must be present. The solution has the ability to resist changes in pH upon the addition of small amounts of either acid or base. Buffers are very important to chemical and biological systems. The pH in the human body varies greatly from one fluid to another for example, the pH of blood is about 7.4, whereas the gastric juice in our stomachs has a pH of about 1.5. These pH values, which are crucial for proper enzyme function and the balance of osmotic pressure, are maintained by buffers in most cases. 

The osmosis phenomenon, stemming from biological systems with biological semipermeable membrane, initially represents a nature net transport of solvent molecules from a region of higher water chemical potential (e.g., dilute solution) to a region of lower water chemical potential (e.g., concentrate solution). The driving force is the pure chemical potential difference, i.e., osmotic pressure difference, across the membrane. 

Osmotic equilibria are important especially in biological systems [2], For example, the cell membranes can be regarded as semipermeable. Inside the cell, the concentration of dissolved substances is considerably higher than outside. Due to the osmotic pressure, water tends to be transported into the cell. To avoid bursting of the cell, there are rigid cell walls with a great mechanical stability, which can absorb the osmotic pressure. Antibiotics like penicillin destroy the cell wall, and water can flow into the cell due to the osmotic pressure, leading to the explosion of the cell due to the osmotic pressure. 

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