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OSMOSIS

Osmosis is very useful in real life such as trees. In order for us all to survive we need

osmosis. for the trees to suck up all the water. And those tress grow (by tress I mean plants) We

eat those plants and animals (that eat the plants/trees) to survive. Considering how important

osmosis for the living activity , so that I decide to write this paper to make us more understand

about what is the osmosis in fact, and what kinds of osmosis application that usually we use in

our daily life.

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Part I

Introduction

In order to attain a working knowledge of osmosis and its effects, i looked through

school textbooks together with some information I had obtained at the library. Many substances

pass in an out of cells by diffusion. Diffusion is the movement of particles from a region where

they are at a higher concentration to a region where they are at a lower concentration. This process

does not require energy from respiration. An example of this is the way cells take up oxygen and get rid of carbon dioxide.

The greater the difference in concentration betIen the two regions, the faster the rate of

diffusion. Small particles also diffuse faster than larger particles. Water passes in and out of

cells by a type of diffusion, called osmosis. Osmosis is the diffusion of water in plants, from a

dilute solution to a more concentrated solution, across a partially permeable membrane; or from

a high concentration to a lower concentration. Put simply, osmosis is the passage of water

across a partially permeable membrane from a dilute to a concentrated solution. When a

substance, such as sugar, dissolves in water, the sugar molecules attract water molecules and

combine with them. The water molecules now combined with sugar molecules are no longer

free to move and so the effective concentration of free water molecules in the solution has beenreduced. The more sugar molecules there are in the solution, the more water molecules will be

't ied up'. In other words, the more concentrated a solution is, the fewer free water molecules it will contain.

Part 2

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by the observed direction of fluid movement, since under this choice the fluid transport is from

high "pressure" to low, congruent with normal fluid flow through pipes from high pressure to

low. The final rationale has to do with the measurement of osmotic pressure by determining how

much hydrostatic pressure on the solution is required to prevent the transport of water from a

pure source across a semi-permeable membrane into the soluton. A positive pressure must be

exerted on the solution to prevent osmotic transport, again congruent with the concept that the

osmotic pressure of the pure solvent is relatively "high".

Nevertheless, the dialog continues on this issue since the discussion of osmosis is most relevant

to the biological and life sciences and perhaps the logic stated above should yield to the

conventions of the field in which the phenomena are most relevant.

Osmosis may occur when there is a partially-permeable membrane, such as a cell membrane.

When a cell is submerged in water, the water molecules pass through the cell membrane from an

area of low solute concentration (outside the cell) to one of high solute concentration (inside the

cell), this is called osmosis. The cell membrane is selectively permeable, so only necessary

materials are let into the cell and waste left out. [4]

When the membrane has a volume of pure water on both sides, water molecules pass in and out

in each direction at the exact same rate; there is no net flow of water through the membrane.However, if there is a solution on one side, and pure water on the other, the membrane is still hit

by molecules from both sides at the same rate. However, some of the molecules hitting the

membrane from the solution side will be solute molecules, and these will not pass through the

membrane. So water molecules pass through the membrane from this side at a slower rate. This

will result in a net flow of water to the side with the solution. Assuming the membrane does not

break, this net flow will slow and finally stop as the pressure on the solution side becomes such

that the movement in each direction is equal: dynamic equilibrium. This could either be due to

the water potential on both sides of the membrane being the same, or due to osmosis being

inhibited by factors such as pressure potential or Osmotic pressure.

Osmosis can also be explained using the notion of entropy, from statistical mechanics. As above,

suppose a permeable membrane separates equal amounts of pure solvent and a solution. Since a

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solution possesses more entropy than pure solvent, the second law of thermodynamics states that

solvent molecules will flow into the solution until the entropy of the combined system is

maximized. Notice that, as this happens, the solvent loses entropy while the solution gains

entropy. Equilibrium, hence maximum entropy, is achieved when the entropy gradient becomes

zero, and dissolution takes place.

Pure water is more ordered than water in a solution; thus, from an entropic standpoint it takes

some net energy to move water molecule from a disordered solution and "pack it in" with pure

water. This is the same explanation as to why the disordered air does not spontaneously separate

and order into oxygen and nitrogen, it would take energy for this to happen. Additionally,

particle size has no bearing on osmotic pressure, as this is the fundamental postulate of

colligative properties.[5]

Ex am pl es of osmosis

Su pp ose an anima l or a pl ant ce ll is pl aced in a so lution of sugar or sa lt in water.

1. If the medium is hypotonic a dilute solution, with a higher water concentration than

the cell the cell will gain water through osmosis.

2. If the medium is isotonic a solution with exactly the same water concentration as the

cell there will be no net movement of water across the cell membrane.

3. If the medium is hypertonic a concentrated solution, with a lower water concentration

than the cell the cell will lose water by osmosis.

Essentially, this means that if a cell is put in a solution which is has a solute concentration

higher than its own, then it will shrivel up, and if it is put in a solution with a lesser solute

concentration than its own, the cell will expand and burst.

F actors

Osmotic p ressure

As mentioned before, osmosis may be opposed by increasing the pressure in the region of

high solute concentration with respect to that in the low solute concentration region. The force

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per unit area, or pressure, required to prevent the passage of water through a selectively-

permeable membrane and into a solution of greater concentration is equivalent to the osmotic

p ressure of the solution, or turgor. Osmotic pressure is a colligative property, meaning that the

property depends on the concentration of the solute but not on its identity.

Increasing the pressure increases the chemical potential of the system in proportion to the

molar volume ( = PV ). Therefore, osmosis stops when the increase in potential due to

pressure equals the potential decrease from

Osmotic gradient

The osmotic gradient is the difference in concentration between two solutions on either

side of a semipermeable membrane, and is used to tell the difference in percentages of theconcentration of a specific particle dissolved in a solution.

Usually the osmotic gradient is used while comparing solutions that have a

semipermeable membrane between them allowing water to diffuse between the two solutions,

toward the hypertonic solution(the solution with the higher concentration). Eventually, the force

of the column of water on the hypertonic side of the semipermeable membrane will equal the

force of diffusion on the hypotonic (the side with a lesser concentration) side, creating

equilibrium. When equilibrium is reached, water continues to flow, but it flows both ways in

equal amounts as well as force, therefore stabilizing the solution.

Bab 3

Conc lusion

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Osmosis is of great importance in biological processes where the solvent is water. The

transport of water and other molecules across biological membranes is essential to many

processes in living organisms.

Refferences

Haynie, Donald T. 2001. B iological Thermodynamics . Cambridge: Cambridge University Press

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