lab report 1 diffusion across biological membrances simulation

7/14/2019 Lab Report 1 Diffusion Across Biological Membrances Simulation

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Ameena Tasneem Bte Mohamed AliS9239311I

Diffusion across Biological Membranes: A simulation

Introduction

Diffusion is the process by which collisions between molecules cause to spread

apart. This movement is described as movement from an area of greater

concentration to an area of lower concentration. Hence, diffusion continues until the

molecules are equally distributed. This is to ensure that molecules have reached a

state of equilibrium. Diffusion occurs spontaneously, no energy is involved.

In cells, Diffusion occurs through cell membrane which is selectively permeable. This

means that some molecules can pass through the membrane while other molecules

cannot. Molecules that move across the membrane through diffusion are either

hydrophobic or small and uncharged. For example, H2O, O2 and CO2. On the other hand, those molecules which did not make through the membrane such as large

polar molecules must be transported through protein mediated mechanisms to cross

the membrane.

Hence, this experiment is focused on diffusion and required to create a own model

cell by pouring distilled H2O, starch, iodine and glucose in tied dialysis tubing to test

for substance which diffuse through the membrane and which one could not due to

its size.

Materials and Methods

Materials:

Distilled H2O

Starch solution

Iodine solution

Glucose solution

Test tube (3-4/group)

Test tube rack

Marking tape

Benedict’s test solution

Hot water bath

Dialysis tubing: 1 inch flat width, pre-soaked

Dialysis tubing: 3 inch flat width, pre-soaked

Breaker

3ml pipette




Methods:

Tract the substance

Step 1: Labeled 4 test tubes as Distilled H2O, Starch, Glucose and Iodine.

Step 2: Add 2ml of distilled H2O, Starch, Glucose and Iodine in the respective test

tubes and add 2ml of Iodine indicator into all 4 test tube.

Step 3: Swirl the test tubes lightly to ensure the Iodine indicator and 4 solutions

mixed well. Observed the colour change closely as shown in table 1.0

Step 4: After Iodine test, rinse the test tube with distilled H2O to ensure all traces of the solution is being washed away and neutralize any charges present.

Step 5: Repeat step 2 with 2ml of Benedict’s solution and swirl the test tubes lightly

and observe the colour change closely as shown in table 1.0

Cell simulation

Step 6: Take 1 inch dialysis tubing and fasten one end of the tube tightly.

Step 7: Pour ¼ full of iodine solution and ½ full of glucose solution and fasten the

other end tightly as well.

Step 8: After which, run 1 inch dialysis tubing under distilled water.

Step 9: Take 3 inch dialysis tubing an repeat step 6.

Step 10: Pour starch solution almost full and submerge 1 inch dialysis tube into 3

inch dialysis tube. Fasten the other end tightly. Again rinse 3 inch dialysis tube with

distilled H2O.

Step 11: Fill the beaker with H2O and submerge the dialysis tubing in and set aside

for 1 hour.

Step 12: After 1 hour, observe the colour change.




Results

Chemical Test Result

Table 1.0 shows the result of distilled H2O, Starch, Glucose and Iodine performed

using Benedict solution and Iodine test. The left column is the 4 different substances

which are used to represent cellular components. The right column is the 2indicators used; Iodine indicator and Benedict’s.

Referring to the table, when both indicators were added to distilled H2O no change

occurred. When starch was added to iodine indicator dark blue precipitate was

formed. Similarly when starch was added to Benedict’s and left it in water bath

3minutes, blue precipitate was formed.

When glucose was added to iodine indicator, no change occurred. On the other hand,

when glucose was added to Benedict’s and left it in water bath 3minutes, brick red

precipitate was formed. Lastly, when iodine was added to benedict’s with 3 minutesof water bath there were no change occurred.

Table 1.0, Chemical test results.




Cell Simulation

Drew the design of our cell simulation as seen on figure 1, and build the cell using 1

inch and 3 inch dialysis tube consist of iodine and glucose and starch respectively.

The dialysis tube was submerged in a beaker filled with water. Both dialysis tubes

were rinsed by distilled H2O before placing them inside and left the cell model aside

for one hour.

After one hour, the 3 inch dialysis tube which carried starch turned dark blue

precipitant.

H2O H2O

From figure 2, we can observe diffusion taking place.’S’ represent starch, ‘i’

represents iodine and ‘g’ represent glucose. As initially, 1 inch dialysis tube consists

of iodine and glucose and 3 inch dialysis tube consists of starch. However, after 1

Figure 1 Design of own cell simulation

g i g i g i g i g

g i g i g i g i g

S S S S S S S

S S S S S S S

g i g i g i

S i i S i

i S i S i S

Initial Stage Final Stage

Figure 2, Diffusion of molecules before and after.




hour, the iodine molecules got diffused into 3 inch dialysis tube and also the water in

the beaker turned slightly cloudy in the final stage.

As changes were observed due to diffusion to confirm, chemical test was conducted

with solution outside the cell, inside of cell and within organelle.

Firstly, extracted solution outside of cell and did Iodine test and Benedict’s test.

Iodine test was conducted to check for the presence of starch by adding 2 ml of iodine indicator into 2 ml of extracted solution outside of cell. However, there were no

visible changes observed. Subsequently added 2ml of benedict’s solution to 2ml of

extracted solution outside of cell and placed them in water bath for 3minutes. The

result obtain was cloudy Therefore assume there was a presence of glucose while

absence of starch and iodine as shown in figure 3.

Secondly, extracted solution inside of cell and did the same tests as earlier to detach

the presence of starch, iodine and glucose. 2ml of the solution was added to 2ml of

iodine indicator to test for presence of starch. Dark blue colour change was observed

through the test. Subsequently, 2ml of benedict’s solution was added with 2ml of solution extracted inside of cell to test for presence of glucose and there was no

visible changes observed. Hence, there were starch and iodine present inside of cell

as shown in figure 3

Lastly, extracted solution within organelle by opening up the tube and added 2 ml of

starch solution to 2 ml of extracted solution. Blue colour was observed during the

test. Subsequently, 2ml of benedict solution added to 2ml of extracted solution and

no visible changes observed. Hence, there was presence of iodine and no presence

of glucose or starch as shown in figure 3.

Figure 3, the current location of each substance after1 hour




Discussion

From the cell simulation modal made, it has explained about the aspects of diffusion

and indicator solution (chemical testing) to test for particular substances. From theobservation made, iodine and glucose have greater concentration due to small

molecular size and also they are monomers. It means their molecules are smaller.

Thus, it diffused out to create a state of equilibrium. On the other hand, starch

molecules did not move by diffusion across a membrane into or out of the cell due to

the large molecular side. This is because many repeated glucose subunits are found

in starch structure. Starch is a polymer. This is the reason why the water in the

beaker or 1 inch dialysis tube did not turn dark blue as no starch molecules diffuse

out.

However, the liquid outside of cell was cloudy. When iodine indicator and Benedict’s test, tested for presence of iodine and glucose respectively, the colour change was

not very distinctive. Hence, we came to a rationale that more time could have

needed for glucose and iodine achieve diffusion as 1 hour was not enough to

complete as perhaps molecules on one side of a membrane become trapped by

binding to macromolecule. On the other hand, perhaps water in the beaker could

have been too diluted so could not detect the presence of glucose and iodine using

indicators. This process is termed as osmosis.

In osmosis, molecules also travel from higher concentration to lower concentration.

However, osmosis only occurs in water. Water molecules are polar and small

enough to pass through the membrane. Therefore, from this experiment, we can

understand that water is essential for cells survival. However, too much of water will

result in hypotonic. cells is placed with a lower concentration, then osmotic pressure

of the extracellular fluid is less than intracellular fluid. As a result, water flow into the

cell causing it to swell and undergo lysis (burst).

Likewise, if a cell is placed into a solution with higher osmotic concentration than the

intracellular fluid such as salt solution. The osmotic pressure of the extracellular fluid

will exceed that of the intracellular fluid casing the cell to shrink and crenate. Hence,it’s hypertonic. This explains why when a small dose of fertilizer can enhance plant

growth but over fertilization can kill the plant. Fertilization has salt and salt

dehydrates the cytoplasm in the cell and would dry up making the cells shrivel up

and die.

Iodine indicators and Benedict’s solution proved that when a substance reacts with

its indicator solution, a reaction will occur and cause a colour change. In this case,

iodine test used to test for the presence of iodine in the solution and Benedict’s

solution is use to detect glucose. It is important for Benedict’s solution to be heated

as it’s a way to prove that it is the mixing of the two that creates the bright orangecolour. If the benedict’s solutions were to be heated separately or the solution to be




heated there will not be any results produced to test the presence of glucose. The

indicator solution will react only if the substance is meant for is present, then it will

react. Else there would not be any changes to observe. Indicators come in handy

when dealing with unknown samples of ingredients to prove what a substance is. A

negative control is used yield a negative result. This is to ensure that all the reagentsare pure and there is no contamination that will give a false result.

Conclusion

In conclusion, we can conclude that diffusion occur spontaneously and molecular

size and charges matters when molecule pass thought cell membrane unless its

molecular size is small and it’s a monomer diffusion will occur spontaneously.

However, if the molecular size is big and it might also hinders the passage way for

smaller molecules to diffuse to a higher concentration to lower concentration to bring

it to an equilibrium state.

We also concluded that cell should maintain a isotonic environment to conduct its

activity smoothly else in hypertonic or hypotonic, it will burst or shrivel and eventually

kills the cell. Therefore, diffusion and osmosis are types of passive transport and

happens spontaneously.

References

http://www.sfponline.org/uploads/336/DiffusionLabReport.pdf

http://faculty.buffalostate.edu/wadswogj/courses/BIO211%20Page/lectures/lab%20pdf's/Diffusion

%20lab%2006a.pdf

http://www.studymode.com/essays/Diffusion-Through-A-Membrane-Lab-462261.html

http://answers.yahoo.com/question/index?qid=20100615085037AAQJsXx

http://www.indiana.edu/~nimsmsf/P215/p215notes/LabManual/Lab5.pdf



http://faculty.buffalostate.edu/wadswogj/courses/BIO211%20Page/lectures/lab%20pdf's/Diffusion%20lab%2006a.pdf














lab report 1 diffusion across biological membrances simulation

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