Cell Structure and Function: Tonicity and pH
CellStructureand Function:Tonicityand pH
LabReportAssistant Thisdocumentis not meanttobe a substitutefora formallaboratoryreport.The Lab ReportAssistantis simply a summaryof the experiment’squestions,diagramsif needed, and datatablesthatshould be addressedin a formallab report.The intentis tofacilitatestudents’writing of lab reportsbyprovidingthis informationin an editablefile which canbe senttoan instructor.
Data Table 1: Comparison of States of Tonicity
Type of Tonicity Gradient: Is the potato strip in a Hypertonic, Hypotonic, or Isotonic
at the beginning of this exercise?
Full with distilled water
Full and healthy in its natural form
The potato strip is in a state of hypotonic in its natural form the cells allows water in due to high solute concentration in the cell
Has a 10% NaCl sodium chloride
Appears shriveled and unhealthy
Though the potato strip is unhealthy, it is still in a hypotonic form
Data Table 2: Comparison of Turgor Pressure States in Elodea Leaf Cells
Scientific Term for Condition:
Is the leaf in a Hypertonic, Hypotonic, or
Isotonic at the beginning of this exercise?
Appearance of Cells at End of Procedure
the leaf is in a hypotonic state before it is immersed in distilled water
Remain same and normal the cell arrangement does not change
Before the leaf is in put in Sodium Chloride solution it is in a hypotonic state
No effect water moves equally in both directions a state of equilibrium exists
Data Table 3: Initial and Ending pH Comparison for Test Tube Solutions
Total drops of 0.1 N HCl added
Buffered protein Albumen (organic) solution
Data Table 4: Results of Acid Addition to Buffered Solutions
Total Drops of HCl Added
Beaker #2 pH
Beaker #3 pH
10-aftersolutionisplacedin beakerand5moredropsofHCl are added
Figure1: Graphof pH Changein ResponsetoBuffering
Drops of HCl
Exercise1: The Case of the Limp Vegetable
A.Howdoes each potatostriplook? Which one is limp and which one is crisp?
Inthe test-tube that has distilled water, the potato strip appearshealthy and its cells are normal the specimen looks different with aswelled shape. This is evident from the cut edges they appear‘blunt’ than before the specimen was dipped in the test-tubecontaining distilled water.
Inthe Sodium Chloride solution, the potato strip appears shrank andwhen felt with fingers, its tissue are ‘rough’ and ‘tough’compared to the strip in the test-tube with distilled water.
Thestrip in the distilled water test-tube is crisp while that in theSodium Solution appears limp
B. Howcanthe differencebe explained?
Inthis context, while the specimen is placed in the two test-tube, eachtest-tube has a solvent that has a different concentration. Distilledwater is neutral compared to the Sodium Chloride solution in theother test-tube. As such, in a hypotonic state, a healthy potatostrip placed in a solution of distilled water absorbs water from thetest-tube and swells. Ideally, a potato strip has high concentrationand this makes it absorb water from outside in order to dilute itscell concentration. Distilled water provides a hypotonic environmentand thus water enters the cells in attempt to dilute itsconcentration and the cells expand, hence the ‘plump’ andswelling like shape(Ananthakrishnan, 2007).In the other specimen in Sodium Chloride solution, the solutionprovided a different environment while the cells have hypertonicenvironment compared to the external environment. This makes thecells lose water making the cell to shrink and become ‘tough’ dueto plasmolysis effect(Alberts, Johnson, Lewis, Raff, Roberts, Walter, 2002).
C. Whatcausedthe changein appearanceof each strip?
Thechange in the nature of the potatoes strips after the experimentcould be attributed to hypotonic and hypertonic conditions of thespecimens used the solvents. In a hypotonic environment, like thedistilled water in the test tubes, water moves in the direction thatwill create an equilibrium condition in both sides. In the case ofdistilled water, the solution is hypotonic and thus enters into thecell to dilute the concentrated nature of the cells. As a result, thecells in turn expand as they take in more water in their vacuolesthereby expanding the cell membrane.
Inthe Sodium solution on the other hand, there exists a hypertonicstate in the solution. The specimen cells have low concentrationcompared to the Sodium Chloride solution. As such, there existdisequilibrium between the cells and the solution. Water thereforesips away from the cells to the solution in an attempt to dilute theconcentrated solution outside their cells. After, sometime of losingwater, the strip thus appears shrunken, ‘tough,’ and limp(Campbell, 2009).
A.Did the exercisesupport or refutethe initial hypothesis?Explain why.
Yes.In every aspect the exercise concurred with the initial hypothesis ofthe study experiment. It was hypothesizes that, in a hypotonicsolution, the cells of a healthy vegetable cell would remain normalwhile in a hypertonic solution the cells of a healthy vegetableplant would change and shrink. The hypothesis in this case was inaccordance to previous experiments on plant cell reactions indifferent solutions of varying tonicity(Alberts, Johnson, Lewis, Raff, Roberts, Walter 2002).
B. Explain whyvegetablesstoredin a refrigeratorovertime becomelimp.
Ina refrigerator, an isotonic environment exists. However, uncoveredvegetables in the refrigerator become limp as the cells lose water tothe isotonic environment. The outside environment does not have waterto support the cells and therefore, the cells become limp.
C.in this exercise,twoof the threetypes of tonicitygradientswereobserved.Suggestan experimenttoprovidean exampleof the thirdtype of tonicitygradientin action.
Inthis case, an experiment to study the isotonic behavior of plantcells would be necessary. In this context, the previous plantspecimens could be used by putting the specimens in a thirdtest-tube either a healthy potato strip or an elodea leaf. However,in this case no solvent would be used but the specimen in thetest-tube could be placed in a refrigerator for one hour. Afterwards,the specimen could be retrieved and their nature observed. Thenconclusions would be made about plant cells behavior in isotonicenvironment.
D.Whatkinds of cell environmentalconditionsmightaffecttonicityin cells?
Basically,the nature and condition of the specimen used matters. Generally, thecells need to be from a healthy plant so that there are able to showchanges when placed in different solvents of varying tonicity. Assuch, the cells need to have a healthy vacuole and cell membranesthat are not damaged or diseased. Specimens whose cell membranes areblocked may not effectively reciprocate to changes in tonicity. Thecells internal conditions may interfere with its capacity to regulatechanges outside its cell walls.
Questions A.Howcanthe differencesin appearanceof the cells in the twosolutions be explained?
Inthe two cases, shape and size of the cells vacuoles differ whichresults in differences when the cells in the two solutions. Under ahypertonic solution, the elodea leaf cells, the vacuoles shrinks whenplaced in hypertonic solution. This is because the cell loses waterto create equilibrium with the external environment thereby makingthe cell look limp and unhealthy. In the other case, in a hypotonicsolution, the cells vacuole absorbs water and becomes full expandingthe pressure on the walls of the cells. The result is that the cellappears turgid and healthy.
Differencein concentration between the distilled water and the Sodium Chloridesolution accounts for the difference in appearance between the twocells Sodium Chloride has high solute concentration and low watercontent compared to the cell. As such, the water moves from the cellto the ‘outside’- Sodium Chloride, in order to dilute theconcentrated solution and maintain a state of equilibrium. Similarly,without external water to support the cell wall, the cell loses itssupport and becomes limp.
C. In whatdirectiondid the watermovein the hypotonicsolution? Inthe hypertonicsolution?
Ideally,in a hypotonic solution the cell absorbs water from the externalenvironment water enters the cell to dilute the concentrated solutein the cells thereby making them more ‘plum’ and rigid. In aHypertonic solution, cells have low concentration of solute comparedto the hypertonic solution outside. This makes water from the cell tomove outside the cell loses water thereby making it less rigid andbecome plasmolysed.
D.Plasmolysisreferstothe movementof waterout of the cell, thus causingthe centralvacuole
Tobecomesmaller.The volumeof the entirecell is reducedand the plasma membranemaybe Visible, separatedfromthe cell wall,becauseit pulls awayfromthe cell wallwith the reductionin volume.In which turgorstatewouldthis be mostlikelytooccur?
Aturgor state occurs when a plant cell is in a plasmolyesed state inthis condition the cell is in a hypertonic solution that makes itlose water thereby making the cell to shrink.
Did this exercise support or refute the initial hypothesis? Explain.
Fromthe analysis of the observations, the exercise fully supported thehypothesis made before the start of the experiment. The hypothesisbased its assumption on previous experiments of this nature, whereplants cells have been found to have varying reactions when indifferent tonicity solutions. The exercise helped to shed more lighton the fact that, hypotonic solutions makes cells become rigid andcrisps as they absorb water from the external environment. In thesame note, the exercise was important in supporting the hypothesisthat cells becomes limp and plasmolysed after losing water tohypertonic solutions. As such, cells in hypotonic appears healthy andfull while in a hypertonic solution, the cells appear unhealthy andless rigid(Campbell, 2009).
B. Wheremightan exampleof this turgorpressureadjustmentbe observedhappening in natureor aroundyourhome?
Theturgor pressure adjustment could be observed plants growing understructures such as houses. Plants exhibit a bending nature as theysearch for water. When in search a state, there are turgor changestaking place within the plant and this requires one to water theplant to offset this condition. Without watering the plant in suchstate, leaves the plant in a flaccid state and with time the plantbecomes excessively plasmolysed and collapse. This is due to lose ofwater from the cells. In another case, when vegetables are put in therefrigerator, they become limp after sometime due to lose of water tothe isotonic state in the refrigerator. The ‘limp’ state ofvegetables in the refrigerator IS different from that of the houseplant the houseplant collapses due to excess plasmolysis while thevegetables in the refrigerator become limp due to isotonicenvironment.
Exercise3: BufferingEffectand pH
A.Whatwasthe initial of the waterin testtube #1?
InitialpH of the test tube #1 was 6.5
B. Whatwasthe pH of the waterafterthe addition of acid?
Afteradding some HCL acid to water its ph was 2.5
C.Whatwasthe initial of testtube solutions#2 and #3?
ThePh stood at 8.0
D.Whatwasthe Phs after adding 5 drops of acid in each of testtubes #2 and #3?
Afteradding 5 drops of acid in test-tube #2 its ph value was 7.9 while theph value of test-tube #3 stood at 7.9
E. When did the pH appreciablychange?
At25 for the inorganic buffer and 45 in the organic buffer test-tube.
F.Whatcausedthis dramaticshift in pH?
Thesedramatic changes in Ph could be attributed to the concentration ofacids added to
A.Did this exercisesupport or refutethe initiallyhypothesis? Explain.
Inthis case, the exercise failed to support the set hypothesis thiscould be attributed to the presence of albumen in the test tubes thatacted as buffers thereby requiring higher amount and concentration ofthe HCl to alter the Ph of the solutions provided.
B. Whydid this patternoccur?
Thepattern observed in the Ph values of the solutions takes after theorganic protein added this albumen had the capacity to withstandacid thereby acting as a strong buffer as well as the other additives
C. Whatwasthe differencebetweensolutions#2 and #3?
Atthe end of the exercise, it was observed that there was anapproximate 4.0 ph difference on overall results. However, test-tubetwo changed more quickly compared to test-tube 3.
D.Whatdifferencewasobservedin the waythe twosolutionsreactedtothe addition of acid?
Thetwo solutions reacted fairly different from each other. However, themain difference was that, solution in test-tube two showed fastchanges than that of test-tube three. In addition, test-tube twosolutions showed its change in Ph earlier compared to solution intest-tube three.
Theunderstanding of this buffering mechanism is important inunderstanding how our body cells fight and expel harmful elementsfrom the environment. Buffer means defense mechanisms in which a cellwould react against a harmful solution which might alter thebiological function of the cell.
Whatdid youlearn fromdoing this laboratory?
Muchwas learned from these laboratory exercises in relation to thebehavioral reaction characteristic of cells when placed in differentenvironments of tonicity. In particular, the plasmolysis andturgidity of plant cells was an insightful observation. I havelearned that plant cells survival is dictated by its turgicalproperties. Healthy plant cells are bound to ‘die’ or becomeunhealthy if the environment does not sufficiently provide them withwater. Assessing my daily observation of bending houseplants, I couldnot grasp why the house plants exhibited such characteristic since Idid not have prior practical laboratory experience to explain thecondition.
Therefore,the experiment is an eye opener on how real life biological functionsof cells can be understood. In particular, the knowledge of Phvariation due to changes or additional of other solutions that alterthe initial Ph, was an insightful experience on how biological cellsfunctions. When acid solution was added to other solutions the buffercharacteristic was observed. I relate this to buffering effectbrought about by vaccines when in the body. The cells are given‘immune power’ to sense and ‘buffer’ against harmfulpathogens. While the effect of vaccine in the human body has noeffects, its effectiveness comes when a harmful pathogen attacks thebody.
AnanthakrishnanR, Ehrlicher A. 2007, ‘The Forces behind Cell Movement.’International Journal of Biological Science 3:303–317.http://www.biolsci.org/v03p0303.htm
AlbertsB, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2002). ‘MolecularBiology of the Cell(4th ed.).’ Garland. ISBN 0-8153-3218-1.
Campbell2009,‘Biology—Conceptsand Connections.’Pearson Education. p. 138.
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