Observation of diffusion and Osmosis in Different Solution Concentrations

Andoni Colmenares

BSC2010C

Section 23

Seat 20

02/24/2010

INTRODUCTION

The cells within the human body are like miniature cities, bustling with energy and

processing many differing substances into new ones in order to sustain balance and life itself

(Campbell et al. 2008). One of the most fundamental processes vital for cell survival is the

ability to move molecules from an area of high concentration to an area of low concentration

(Campbell et al. 2008). In the process known as diffusion, molecules move with the

concentration gradient in response to the tonicity around the cell (Campbell et al. 2008). The

important cellular process of osmosis allows cells to absorb or release water when there is a

change in the concentration of the solute or the solvent within or around the cell (Campbell et al.

2008). Without these important cellular characteristics many fundamental life sustaining

processes, such as breathing, would not be possible (Campbell et al. 2008). Also the amount of a

specific substance in the body can often are a life or death factor. The calculation of the different

levels of substances diffused in a cell is highly important for patient assessment and

consequently patient care (Caon, 2). Yearly new substances are being synthesized and it is

important to learn about their effects on this necessary life sustaining process (Xibao 2010). To

more thoroughly understand the process of osmosis and diffusion, further information must be

covered.

When a liquid is completely mixed with two substances it is called a solution (Campbell

et al. 2008). A Solvent is the substance doing the dissolving and a solute is the substance being

dissolved (Campbell et al. 2008). In an aqueous solution water is said to be the solvent

(Campbell et al. 2008). Substances naturally move within a cell from areas of high to low

concentration (Campbell et al. 2008). There is said to be a concentration gradient when there is a

difference between solvent and solute and movement between the concentrations (Campbell et

al. 2008). This movement of substances occurs through membranes, within the cell, which

separate the two different concentrations (Campbell et al. 2008). The plasma membrane of cells

allows selective admittance or no admittance of substances in and out of the cell (Campbell et al.

2008).

According to Campbell et al. (2008) Cells contain semi permeable and or impermeable

membranes. In an impermeable membrane substances are not able to travel through the

membrane to the other side (Campbell et al. 2008). Semi permeable membranes are selective but

they permit some things to go through them (Campbell et al. 2008). In a semi permeable

membrane substances are moved through the membrane by either active transport or passive

transport (Campbell et al. 2008). Active transport requires energy because it uses transmembrane

proteins, proteins moving through membranes, called transporters to move against their

concentration gradient (Thomas et al. 2010). On the other hand, passive transport moves

substances from an area of more to less concentration (Thomas et al. 2010). No energy is

required during passive transport because substances flow with the gradient (Thomas et al.

2010). Diffusion is a type of passive transport which is influenced by the solute concentration

within the cell and the solute concentration of the cell's surroundings (Thomas et al. 2010).

Osmosis is a form of diffusion which describes water molecules moving through a semi-

permeable membrane from higher to lower concentration (Thomas et al. 2010). The ability of a

cell to perform osmosis, that is to gain or lose water, is influenced by tonicity (Campbell et al.

2008). Tonicity is the how the solution around the cell affects the absorption or evacuation of

water into or out of the cell (Campbell et al. 2008). Through the process of osmosis water can

make a cell isotonic, hypertonic or hypotonic (Campbell et al. 2008) According to Campbell et

al. (2008) If the amount of solute inside and outside the cell is equal and there is no net change of

water the cell and solution are considered to be isotonic. If there happens to be more solute

outside the cell, the selectively permeable membrane will allow water to leave the cell (Campbell

et al. 2008). In this case the cell is considered hypertonic; diffusion actually causes the cell to

shrivel up (Campbell et al. 2008). In a hypotonic solution the tonicity accounts for the cell's

expansion as well (Campbell et al. 2008). There is more water rushing into the cell because there

is a higher concentration of solute in the cell (Campbell et al. 2008).

The selectively, permeable membrane is essential to living cells because it allows

necessary substances to enter and it impedes unnecessary ones (Campbell et al. 2008). The lipid

bi-layer allows sugars, such as glucose, to pass through it which in turn provide energy for the

cell (Campbell et al. 2008). If the membrane did not allow the glucose to enter, it would not be

converted into expendable energy for the cell to use (Campbell et al. 2008).

Now diffusion is vital to plants and animals cells because substances have a tendency to

move from areas of higher to lower concentration (Campbell et al. 2008). According to Campbell

et al. (2008) without diffusion the semi-permeable membrane would not have any way to move

substances through it. The cell's energy making process would not be able to even start

(Campbell et al. 2008). If a cell does not have a permeable membrane substances would not be

able to pass through and the cell would die (Campbell et al. 2008). If tonicity was not a factor

cell's would not be able to rely on the energy less process of diffusion and osmosis which deliver

nutrients to the cell and drive energy making processes (Campbell et al. 2008). Therefore the

permeability of a membrane and the tonicity of the solution, which fuels passive transport and

diffusion, are significantly important to a cell's well being (Campbell et al. 2008).

The lab experiment involves osmotic diffusion through a semi-permeable membrane.

There are four different controlled variables involved. Each variable contains a potato piece and

a greater or lesser concentration of glucose in each solution. Each variable has different

tonicities. After the experiment the weights of the potatoes may differ according to the flow of

osmosis. Through passive transport water will move from levels of higher to lower

concentration. The null hypothesis states that the differences in glucose concentration will

neither affect the weight nor the size of the potatoes. The alternate hypothesis states that the

potatoes weight and size will change according to the differences in glucose concentration.

METHODS

All methods of this lab report were taken from Biology 1 (Thomas et al. 2010)

To begin the experiment my partner and I acquired a potato and proceeded to bore four

holes into the potato using a cork borer. We then cleaned the skin of each potato and used a

metric ruler to measure each piece. We cut each potato cylinder into lengths of three centimeters

each. Then my partner and I placed each potato slice into separate cups and labeled the cups:

dH20, 0.25M, 0.50M and 1.0M. Afterward we went to the balance station and used the weight

boat to make sure the balance was at zero. The weight boat is a plastic piece that we place on the

scale to make it balanced at zero. My partner and I removed each potato piece from each cup,

then individually placed and weighed the potato cylinders on the weight boat. We wrote down

the values after each weigh in. Then we wrote down the weights on a table in the row labeled

weight before and under the column which corresponded to each cup. Following this, my partner

and I poured 20 to 25 ml of dH20 or sucrose solution into each relevant cup. Thereafter, we let

the potatoes soak for one hour and fifteen minutes. Ensuing this, my partner and I dried off any

excess solution from the potatoes by slowly drying them on a paper towel. Then we removed

each potato from each cup and weighed the cylinders on the same weighing scale as we did

before we added the solutions. We recorded the weights on the row labeled weight after and

under each respective column. Afterward we found the difference of the before and after

weights. We found the difference by subtracting the before weight, of each cup, from the after

weight of each cup. Then we used the percent change formula to get the percent change of the

two values. The percent change formula states final value minus initial value divided by initial

value multiplied by a factor of one hundred.

RESULTS

After my partner and I conducted the experiment we found that there was a visual size

and calculated weight increase among the potatoes. The cup labeled dH2O had a before weight of

0.94g and an after weight of 1.07g. This was the heaviest potato and it certainly appeared to have

increased in size. There was a 0.13g difference between the before and after weight of this

potato. The calculated percent change was 13.8%. The next potato labeled 0.25M had an initial

weight of 0.97g and an after weight of 1.01g. The difference between the before and after weight

was 0.04g. The calculated percent change was 4.1%. The potato in the cup labeled 0.50M had an

initial weight of 1.0g and an after weight of 0.9g. The difference between the before and after

weight was -0.09g. The calculated percent change was -9% for this potato. The potato in the final

cup labeled 1.0M had a before weight of 0.94g and an after weight of 0.78g. This potato

noticeably shrank in size. The difference between before and after weight was -.016g. The

percent change calculated was -17%.

0M (dH2O) .25M .5M 1M5 3.88 -10.89 -14.29

25.3 0 -29.1 -2115.625 12.63 2.94 -6.2518.09 12.5 7.53 -8.255.94 -3.81 -10.5 -17.914.3 10.8 6.82 -4.175.05 -1.05 -7.84 -18.75-2.7 -2.7 -13.4 -21.87.45 1.04 -6.38 -18.485.2 1.05 -4.06 -19.78.2 1 -5 -167.8 -1.06 -7.87 -19.57

23.17 9.57 5.56 -2.3311.1 0.95 -5.05 -13.4-8.47 -11.1 -25 -25.7-0.925 -9.615 -12.121 -19.3879.09 0 -11.54 -25.2416.87 15.07 2.78 -22.55.1 1.02 -11.46 -18.183 -3 -9 -14

2.13 -2.88 -10.58 -243 -1.2 -4.7 -13

8.1 2.7 -4.6 -16.55.2 -2 -11.2 -20.2

Average

8.025833333

1.408125

-7.2775

4

-16.691

5Sta. Dev.

7.843049078

6.572027

8.756984

6.308652

Table 1: Class average and standard deviation of percent changes

0.00 0.25 0.50 1.00

-20

-15

-10

-5

0

5

10Pe

rcen

t Cha

nge

Solution Molarities

Figure 1: Average percent changes with standard deviation

DISCUSSION

The null hypothesis of this experiment stated that the differences in glucose concentration

will neither affect the size nor weight of the potatoes. The alternate hypothesis stated that the

weight and size of the potatoes will change according to the differences in glucose concentration.

After reviewing the results yielded I accept the alternate hypothesis and I reject the null

hypothesis because there were apparent weight and size differences among the potatoes in

varying glucose concentrations. The results of the experiment showed a steady decrease in the

size and weight of the potatoes as the concentration of the glucose in the solution increased. The

first potato, that was placed in a solution with no glucose, grew the largest and weighed the

heaviest after conducting the experiment. The cells in this potato, containing a water solution,

absorbed the most water thereby raising the weight of the potato significantly. The 13.8%

calculated percent change occurred because of the tonicity of the potato's solution. There was

much more water in the potato cells' solution then in the potato cells themselves. There was also

a greater amount of glucose in the potato than there was outside in the solution. Through osmosis

the water diffused through the potato cells' semi permeable membrane from an area of higher to

lower concentration. The second potato, placed in the solution labeled 0.25M, also increased in

weight and size. Although there was glucose in this potato's environment, the amount of glucose

in the potato was still greater than the concentration of glucose outside in the container. Because

the solute was still greater within the cells than in the cell's solution, water rushed into the potato

through osmosis thereby increasing the after weight and visual size of the potato. The potato,

placed in the cup of solution labeled 0.50M, had a lower final weight than initial weight. The

difference between the before and after weight was -0.09g. The potato placed in this solution

released more water than it gained. The potato and its solution are considered hypertonic. The

cells in this potato lost water because the concentration of glucose was higher in the solution that

the potato was placed in. Water evacuated the cells of the potato, due to the tonicity, resulting in

a decreased weight and size of the potato. The potato placed in the solution labeled 1.0M

weighed the least after the experiment and had the highest, most negative, percent change. This

potato had a -17% percent change which resulted in decreased potato size and weight. The

increased concentration of glucose, or solute, in the solution and the lesser amount of solute

within the potato cells caused the potato cells to lose water. The cells actually shrank as osmosis

carried water through the semi-permeable membrane out of the cells and into the solution which

the potato was placed in.

When the solute inside the cell is higher than the solute in the cell's environment, water

will naturally diffuse from higher to lower concentration (Campbell et al. 2008). The first two

potatoes, placed in solutions of only water and 0.25M glucose, both gained water and

consequently increased in after weight. These two potatoes are considered to be hypotonic. The

water diffused into the potato's cells which swelled them. On the other hand the other potatoes,

placed in cups labeled 0.50M and 1.0M, had a lower after weight than before weight. The solute

in the potatoes' solution was more concentrated so water diffused out of the potato cells. These

potatoes are considered to be hypertonic because osmosis caused water movement out of the cell

and into the solution (Campbell et al. 2008). Through passive diffusion water moved in and out

of these potato cells from higher to lower concentration depending on the concentration of solute

in the potato and solution (Campbell et al. 2008).

After the results of this project I will conduct another experiment involving different

substances than glucose. I will conduct a similar experiment to this one except I will use four

different solutions in different concentrations instead of differing concentrations of the same

solution. I will use solutions mixed with substances of only water, salt, and several different

sugars. The goal of this project will be to observe the effects of the four substances and many

concentrations of those substances and observe the impermeability of those substances. The

purpose of this project will be to gain a better understanding of the effects of different substances

on osmosis. As new substances are synthesized, such as gold nano-particles, it is important to

know how the diffusion of water is affected by the solutes that are in it (Xibao et al. 2010). The

results of this experiment are significant because the ability of water to diffuse through a

membrane, due to the concentration of solute in the aqueous solution, affects how our body's

cells conduct osmosis when certain solutes are present (Caon 2010). In the medical field it is

important to know the concentration of certain solutes because this affects patients when there is

a increase or decrease in the concentration of that substance (Caon 2010). At the hospital, nurses

regularly check the concentration of certain substances in the patient's body in order to make sure

that the patient is stable (Caon 2010). Therefore further exploration on this topic is important to

both people in the medical field and their patients alike.

Works Cited

Campbell, N. Reese, J. Urry, L. Cain, M. Wasserman, S. Minorsky, P. Jackson, R. 2008. Biology

. 8th edition. Pearson Publishing. San Francisco, Ca. 536 pages.

Caon, Martin. 2010. "Osmoles, osmolality and osmotic pressure: Clarifying the puzzle of .

solution concentration." Contemporary Nurse: A Journal for the Australian Nursing . .

Profession .29.1 (2008): 92-99.

Thomas, P. Walters, L. Boyers, B. Yeargain, M. 2010. Laboratory Manual for Biology 1, 16th .

edition.

Xibao G, Hongyin Y, Jiang Y, Ning L, Jinghe Y. 2010. Protein Enhanced Near-Infrared .

Fluorescence of AuNPs and Its Application for Protein Determination. Analytical Letters

. [serial online]. April 2010;43(4):701-710.