Nutrients Osmosis

Membrane transport Once a membrane has formed, nutrients have to be transported across the membrane either by osmosis or actively... 

Osmometry is used to determine the molar masses of polymers and natural macromolecules osmosis helps to transport nutrients in plants reverse osmosis is used in water purification. 

In Chapter 13, you learned that diffusion is the mixing of gases or liquids resulting from their random motions. Osmosis is the diffusion of solvent particles across a semipermeable membrane from an area of higher solvent concentration to an area of lower solvent concentration. Semipermeable membranes are barriers with tiny pores that allow some but not all kinds of particles to cross. The membranes surrounding all living cells are semipermeable membranes. Osmosis plays an important role in many biological systems such as kidney dialysis and the uptake of nutrients by plants. 

Edible film Controlled moisture transfer between food and the surrounding environment Controlled release of antimicrobial substances Controlled release of antioxidants Controlled release of nutrients, flavors, and drugs Reduction of oxygen partial pressure Controlled rate of respiration Temperature control Controlled enzymatic browning in fruits Reverse osmosis membranes... 

Vs we have seen in Section 7.8, blood is the medium for exchange of both nutrients and waste products. The membranes of the kidneys remove waste materials such as urea and uric acid (Chapter 22) and excess salts and large quantities of water. This process of waste removal is termed dialysis, a process similar in function to osmosis (Section 7.6). Semipermeable membranes in the kidneys, dialyzing membranes, allow small molecules (principally water and urea) and ions in solution to pass through and ultimately collect in the bladder. From there they can be eliminated from the body. 

The ubiquitous role of chloride (as dissolved sodium chloride) in animal and human cells and blood plasma is manifold as just discussed, it provides Cl for organosynthesis and to control the electrolytic properties such as osmosis (a process where water molecules move through a semipermeable membrane from a dilute solution into a more concentrated solution), for nutrient and waste transport, as well as providing electrical gradients (based on conductivity) for information transfer through neurons. 

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. 

In osmosis water moves from an area of high water concentration (low solute concentration) into an area of low water concentration (high solute concentration). The movement of a substance from an area where its concentration is high to an area where it is low is spontaneous. Biological cells transport not only water, but also other select materials through their membrane walls. This permits nutrients to enter and waste materials to exit. In some cases substances must be moved from an area of low concentration to one of high concentration. This movement— called active transport—is not spontaneous, so cells must expend energy to do it. 

An example described in detail in this chapter shows that a reverse osmosis membrane can also be used for the separation of the product from the mixture of microorganisms, substrates, and nutrients. Often, microorganisms and enzymes that act as biocatalysts are immobilized to membranes, mostly to hollow fiber membranes. 

A bioreactor in which living yeast cells are sandwiched between a cellulose acetate ultrafiltration membrane and a cellulose acetate reverse osmosis membrane (Figure 9.1) was proposed [280], [281]. A solution containing glucose substrate and nutrients is in contact with the ultrahltration (UP) membrane, and pressure is applied on the substrate solution. The substrate permeates the UF membrane freely, together with solvent (water), and arrives at the cell layer where the bioreaction starts to occur, leading to the ethanol product. When the solution is forced by pressure out of the cell layer from the side that is in contact... 

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