Title
Membrane Permeability
Objective
1.
To
define the solvent, solute, solution, selectively permeable, diffusio n, osmosis,
concentration gradient, equilibrium, turgid, plasmolyzed, plasmo lysis, turgor pressure, tonicity, hypertonic, isotonic, and hypotonic. 2.
To
describe the effects of hypertonic, isotonic and hypotonic so lutions on Elodea leaf
cells and onio n scale leafs.
Introductio n
All bio logical cells are surr ounded by a boundary layer called a plasma membrane. The
cell membrane is a bio logical membrane that separates the interior of all cells fr o m
the outside envir onment. Due to the living cells are made up of 70%-85% water, so that all the substances are disso lved in the water and moving enter or leaving the cells. The cell membrane is selectively permeable to ions and organic molecules and contr ols the mo vement of substances in and out of the cells. For example, salt and sugar need to disso lve in water bef ore they enter or leave the cells and it is easier f or the movement pr ocess of the substances.
The The
cell membrane consists of the phospho lipid bilayer with embedded pr oteins.
phospholipid bilayer contains hydr o pho bic tail regions (surr ounding po lar fluid) and
hydr o philic head (cytosolic and extracellular faces) of the resulting of bilayer. The bilayer membrane contr ol the polar molecules to acr oss the membrane, due to it is a selective permeable membrane. Some pr otein mo lecules in the membrane act as channels or
gates to regulate the transport of bio materials in and out of the cell. The help of using
transmembrane pr otein to overcome the other bigger size mo lecule to passes thr ough the membrane.
For a cell to survive, it must be constantly supplied with nutrient and metabo lic waste pr oducts must be removed. All bio mo lecules that enter or exit the cell encounter
the plasma membrane barrier. Certain small, non-polar mo lecules can readily diffuse d iffuse thr ough the membrane. Other mo lecules, specifically those that are large and polar, require the assistance of pr otein channels, carriers, gates, and pumps to achieve transport.
All f orms of membrane transport can be classified into one of two major gr oups, which is passive transport and active transport. Passive transport us a mo lecule or ion that cr osses the membrane by mo ving down a concentration (move fr om a region of higher concentration thr ough a permeable divider to a regio n of lower concentration of that solute) or electr ochemical gradient and without expenditure of metabolic energy. There have two kind of passive transport which is simple diffusio n (invo lve no pr otein) and facilitated diffusio n (involve pr otein).
Simple diffusio n is an unassisted net movement of a solute fr om a region where its concentration is higher to a region where its concentration lowers. Simple diffusio n occur
without the using of energy. It lets gases, non-po lar molecules and small polar
mo lecules such as water, carbon dioxide, oxygen or ethanol passes thr ough the membrane. The
main factor affecting the diffusio n of solute is the size of so lute, the polarity o f solute
and the charge of solute.
Water also can acr oss the selectively membrane by using the pr p r ocess of osmosis. It is permeable to water but not to the dissolved solute. Osmosis is the water move fr om regions of lower solute concentration to regions of higher so lute concentration. Water will tend t o move inward because the concentration of so lutes is always higher inside a cell than outside. Osmotic movement of water into and out of a cell is related to the larity osmo larity
(relative (re lative so lute concentration), of the solution in which the cell finds itself.
A concentration gradient is the concentration that exists between a two different areas. When the concentration between both sides is equally the same, the t he system is said to be equilibrium, there are no net flow of particles or ions in the system. Although the system was equilibrium in the cells, while the p articles still flow ar ound and move ar ound. The
movement of the particles will not affect the change in the concentration.
Plant cells consist of cell wall which pr otect the interior and maintain the shape of
the cell. The vacuo le in plant cells aid as st orage of f oo oo d and nutrient. While the
vacuo lar membrane is selectively membrane, so that only so me o f the particles can move in. Water can move in and out though the membrane, this causes the turgor pressure. This mean main pressure of the cell contents against the cell wall in plant cells and bacteria cells, determined by the water content of the vacuole, resulting fr o m osmotic pressure. Theref ore
the cell was turgid. tu rgid.
Material y
Forceps
y
2 micr osco pe slides
y
2 coverslips
y
Compound micr osco pe
y
Elodea in tap water
y
2 dr o pping bottles od dH2O
y
2 dr o pping bottles of 20% sodium chloride (NaCl)
Method
1. A f orceps was used to remove two young leaves fr om the tip of an Elodea plant. 2. One leaf was mounted in a dr o p of distilled water on a micr osco pe slide and the other in 20% NaCl so lution on a second micr osco pe slide. 3.
The coverslips
4.
The
were places over both leaves.
leaf in the distilled water was o bserved with the compound micr osco pe. The
medium-power o bjective was used to f ocus first and then the high-dry o bjective was switched. 5.
The
leaf mounted with 20% NaCl so lution was o bserved now. After several minutes,
the cell will have lost water, causing it to become plasmo lyzed. (plasmo lysis) 6.
Deplasmolysis was o bserved by slowly and gently remove the coverslip fr o m a preparation exhibiting plasmo lysis, the salt solution was drained and 2 dr o ps of distilled water was added.
7. After 1 minute, a coverslip was placed on the preparation. Under the examined at high-dry f or 5 minute, the result was o bserved.
R esult esult
Discussion
When o bserve the Elodea leaf under the compound micr osco pe, we can f ound that the Elodea leaf contain cell wall, plasma membrane, cyto plasm, vacuo le and chlor o plast. Every organelle in the plant cell has its own function to help the plant cell to survive. The main organelle that we f ound in the plant ce ll is the cell wall. It is used to fix the shape of the plant cell. It is t ough, usually flexible but sometimes fairly rigid layer that surr ounds some types of cells. Plant cell wall is the major in carbohydrate, which is cellulose, hemicellulose and pectin. The cell wall o f the plant cell is semi-permeable and permits the passage of small mo lecules (oxygen and carbon dioxide) and small pr otein. One of the important cell wall functions is pr oviding strength to the cell. Although the cell wall is rigid in nature, it is also flexible to a certain extent. Besides, the cell wall is the first line of defense f or the cell during an att ack fr o m pathogens and micr oo oorganisms. Its pr o perty o f being rigid is to prevent pathogens and other harmful f oreign bodies fr o m entering. It also offers pr otection against mechanical stress to the cell.
Bef ore entering the cyto plasm, there have a membrane below the cell wall which is plasma membrane. The plasma membrane function that pr o bably is of greatest significance to the cells is the transportation of materials. This semi-permeable membrane of
the cells helps in the transferring of the nutrients and chemicals that are required requ ired f or
the cell functioning. The other f oreign materials are o bstructed on their path thereby preventing the invasio n of the plasma membrane.
Cyto plasm is the interior organelle f ound in both animal and plant p lant cell. The function cyto plasm is to pr ovide support to the internal structures by being a medium f or their suspensio n. It also help in maintaining the shape and consistency of the cell. Besides, it also stores many chemicals that are inevitable f o r life.
The They
two organelles which is vacuo le and chlor o plast does not f ound in animal cell.
play a very important f or the plant cell. The large vacuo le in the plant cell in
enclo sed by a semi-permeable membrane called tono plast. The function of the vacuo le in the plant cell is to store organic and inorganic substances. The all chemicals invo lve
organic
acid, sugars, mineral salts, oxygen, carbon dioxide, amino acid and waste pr oduct
substances. It also maintains maintains the internal hydr ostatic pressure or turgor within the cell. For chlor o plast, it contains an important component of a plant cell called chlor o phyll, which is responsible f or pr oduction of f oo oo d. It's the chlor o phyll which gives the leaves its characteristic green co lor. It absorbs the sunlight to undergo the pr ocess of photosynthesis.
When the Elodea leaf mounted with distilled water, o bserve under the compound micr osco pe, the plant cell beco me turgid and rigid. This is because the concentration inside o f the vacuo le in the plant cell is much higher than t han concentration outside of the plant cell. When undergoes the pr ocess of osmosis, the water will mo ve into the cell membrane then finally to the vacuole. It also creates the turgor pressure that means the vacuo le push the cyto plasm against the cell wall and support the structure of plant cell. The
cell membrane just can only expend until the maximum that the water molecules
cannot moving into the cell. In the other hand, when the plant cell put in 20% of NaCl, the cell will become plasmo lyzed. This is due to the plant cell was put in the hypertonic so lution, which is high in so lute concentration. The cell finally become shrinks together because the water diffuses out fr om the plant cell by osmosis. This causes the vacuole and the cyto plasm to lose water to the surr ounding. This pr ocess is known as plasmo lysis. The cell beco mes flaccid and not turgid anymore. While the cell wall maintain the shape due to it is str ong enough.
Due to the concentration gradient, when the plasmolyzed plant cell water immersed into hypotonic so lution, the cell will become turgid again, due to the interior of the cell is higher concentration than the concentration at outside envir onment. Hypotonic is the condition where the content inside the cell having a lower osmotic pressure than a particular fluid.
The
Elodea cell is to be said deplasmo lyzed.
To nicity
is the osmotic pressure or tensio n of a solution, as in the
cells would swell or shrink depending on the tonicity of the envir onment. In hypotonic solution, the concentration of so lute is lower in this solution when compared with others solution. The so lutions which are in equal concentration mean it is isotonic. The solution with lower concentration of so lute is called hypotonic so lution.
Conclusion The so lvent, solute, solution,
selectively permeable, diffusio n, osmosis,
concentration gradient, equilibrium, turgid, plasmolyzed, plasmolysis, turgor pressure, tonicity, hypertonic, isotonic, and hypotonic was defined.
Solute is a component of so lution, which disso lved substance in the so lvent. While so lvent is a liquid, solid, or gas that disso lves another solid, liquid, or gaseous solute, resulting in a so lution that is so luble in a certain vo lume of solvent at a specified temperature. Solution is a ho mogeneous mixture composed on only one phase. In the mixture, a solute is dissolved in the solvent. Selectively permeable mean a feature and a function of the plasma membrane that is essential to maintain ho meostasis by regulating the passage of so me substances while preventing others fr om entering the cell.
Diffusion is the movement of the particles acr oss the membrane fr om a region of higher concentration to a region of lower concentration area. Osmosis is the diffusio n of water acr oss the plasma membrane fr om a region of lower so lute concentration to a region of higher so lute concentration. The concentration gradient is the difference o f concentration of like mo lecules in two regions. Equilibrium is state of rest or balance due to the equal mo vement of the particles.
Turgid
in another word mean swo llen or tumid. It means the plant cell ce ll will not
burst and just swollen and turgid. Plasmo lyzed mean that it undergoes the pr ocess of plasmo lysis and plasmo lysis is the pr ocess in plant cells where the plasma membrane pulls away fr om the cell wall due to the loss of water thr ough osmosis. Turgor pressure mean main pressure of the cell contents against the cell wall in plant cells and bacteria
cells, determined by the water content of the vacuole, resulting fr o m osmotic pressure. To nicity
is the osmotic pressure or tensio n of a solution, as in the cells would swell or
shrink depending on the tonicity of the envir onment.
When the Elodea leaf in the hypert onic solution, the water in the cell ce ll will mo ving outward
causes the cell to shrink, due to Elodea leaf consists of cell wall, so it can
maintain the shape of the cell. While in hypotonic solution, the water at the outer will mo ving inward to the cell, causes the cell to become turgid, but do not burst due to the cell wall maintaining the shape. Lastly, in isotonic solution will not affect the movement of
the water because it is equilibrium at the interior and exterior. For overview, under the view of micr osco pe the structures that can be seen are
cell wall, plasma membrane, vacuole, cyto plasm and chlor o plast. The plant cell like Elodea cell has a membrane that can regulate the mo vement of water in and out of the cell. The cell wall help to maintain the turgid shaped of plant cell. The absent of cell wall in plant cell, the plant will beco me rapture and unshaped. Vacuole is important to function in maintain the water balance in the cell. The concentration of so lute inside the cell is important to determine whether the plant is in hypertonic, isotonic or hypotonic condition.
Questio n
1. Were the contents of the vacuo le in the Elodea leaf in distilled water hypotonic, isotonic, or hypertonic co mpared to the water? A: It is is otonic to the water when the content of the vacuo le in the Elodea leaf in distilled water.
2. Was the 20% NaCl solution hypertonic, isotonic or hypotonic relative to the cyto plasm? A: The 20% NaCl so lution is hypertonic relative t o the cyto plasm.
3.
If a hypotonic and a hypertonic so lution are separated by selectively permeable membrane, which direction will the water move? A: The water will mo ve fr om hypotonic so lution into hypertonic so lution if it is separated by the selectively permeable membrane.
4.
Name two selectively permeable membranes that are present within the Elodea cells and that were involved in the plasmolysis pr ocess. A: The two selectively membrane that is presents within the Elodea cells and that were involved in the plasmo lysis pr ocess are plasma membrane and vacuo le membrane.
R efere eference
1. Sonia.Nair, Cyto plasm Function, fr om http://www.buzzle.com/articles/cytoplasm function-in-a-cell.html th
2. Becker,W.M., Kleinsmith,L.J.,& Hardin,J. (2009), T he he world of the cell . (7 ed.), San Francisco: Pearson/Benjamin Cummings. 3.
th
Campbell,N.A.,Reece,J.B.,&Mitchell,L.G.(2008), Biology. iology. (8 ed.), San Francisco: Pearson/Benjamin Cummings.
