Diffusion and Osmosis Lab Report

Cell Size and Diffusion Investigation Lab Report (9/29/2019)

Background Info

Diffusion

Diffusion is the thermal movement of solutes from an area of low concentration to an area of high concentration in order to achieve equilibrium. Diffusion takes place in our own bodies, an example being in cellular respiration. In this metabolic reaction, oxygen diffuses down the concentration gradient (an area where the compactness of a chemical material increases or reduces) into the cell through a selectively permeable plasma membrane, allowing cellular respiration to take place. Diffusion requires no energy and thereby is a form of passive transport.

Osmosis

The diffusion of water molecules through a selectively permeable membrane is osmosis. Osmosis is crucial to our existence, as the process of osmosis maintains homeostasis (relatively stable environment) in the human body and allows the exchange of nutrients between cells (Palaparthi, 2017). The rate of osmosis is affected by temperature, pressure, and size. In temperature, more heat causes more energy. More energy allows the molecules to collide more, which gives away to faster diffusion rates. More pressure causes more molecules to collide. Colliding molecules rub off energy, causing diffusion rates to increase. The larger the cell size, the more energy required for diffusion, thus elongating the time of diffusing, consequently decreasing the rate. The rate of diffusion relative to cell size was tested when three agar cubes of different sizes were measured after being placed in cups of vinegar for 10 minutes. A hypothesis suitable for this experiment is if the surface area of the cell size is larger, the extent of the diffusion in percentages would decrease as it would take a longer time for diffusion to take place within the cell if it has a larger surface area.

Cell Size

When a cell has a higher solute concentration than the environment, water will move into the hypertonic cell through osmosis. When a cell has a lower solute concentration than the environment, water will diffuse out of the hypotonic cell through osmosis in order to achieve equal concentrations, in which the cell would be isotonic. The concept of cell size was demonstrated in measuring the mass of 18 turnip cores before and after being placed in six beakers filled with different sucrose molarities. A hypothesis suitable for this experiment is if the molarity of the sucrose concentrations increases, then the cell's size would initially be increasing less and eventually the cell's size would be decreasing. Water molecules, initially, would be diffusing into the turnip core, but the water would be diffusing out of the turnip core later on as the molarity is increasing.

Demonstration Info (Dialysis)

A dialysis tube of 1% starch solution and glucose was placed into a beaker of water and IKI (Lugol's iodine/Potassium Iodine). When the 30 minutes went by, the dialysis tube was of darkish purple color. The reason for this change in color was because of a chemical reaction where the iodine dissolved into the IKI solution, which consequently interacted with the starch.

The targets of this laboratory experiment were to explore rates of diffusion relative to size and size changes relative to different molarity concentrations.

Methods and Materials

Procedures for Turnip Core Experiment

In the first experiment testing changes in size relative to different molarity concentrations (the independent variable), 18 turnip cores were picked from a 3-centimeter slice of a turnip by a coring tool. After being plucked out, the turnip cores were measured using a balance. After being measured, the turnip cores were placed in five cups of sucrose with different molarity concentrations (.2M, .4M, .6M, .8M and 1M) and color to keep the turnip cores straight (red, yellow, brown, green and blue) and the control group: a cup of water (dH₂O), which were all about 200mL (measured in the graduated cylinder before being placed into the beakers). After 10 minutes, the turnip cores were tested for their change in mass (dependent variable). Once the percent of change in mass was calculated, the molarity was determined through the solute potential equation.

Procedures for Extent of Diffusion Experiment

In the second experiment testing rates of diffusion relative to the surface area, 3 agar cubes of different sizes (1cmx1cmx1cm (control to compare with), 2cmx2cmx2cm, and 3cmx3cmx3cm (independent variables)), were carefully formed from one huge agar block. Afterward, the volume, surface area, and the SA:V ratios were measured. The agar cubes were then placed in a solution of white vinegar for 10 minutes and were measured afterward for the extent of diffusion. The extent of diffusion, the dependent variable, was measured by subtracting the volume of the cube that was uncolored from the total volume of the agar cube divided by the total volume of the agar cube. The percentages were recorded for each agar cube.

Procedures/Explanation for Demonstration Experiment (Dialysis)

We performed dialysis tubing, where a bag of 1% starch solution was placed into a cup of water with IKI for 30 minutes. After the 30 minutes, the bag changed into a dark, purple color, indicating that IKI diffused into the bag and the glucose and starch became evident. A chemical interaction occurred between the IKI and the starch, which caused the bag to turn into a black color. This demonstration showcases the scientific process of diffusion in simple terms for us as students, which was taught to us in the classroom. This process of diffusion is played out in our own bodies! Our cells' selectively permeable cell membrane allows different substances to diffuse in and out of the cell in order to maintain homeostasis (isotonic). This is known as osmoregulation.

Results

Change in Mass of Turnip Cores (%)

Color of Solution	Initial Mass (g)	Final Mass (g)	% change in mass
Clear	5.12g	5.32g	100((5.32g - 5.12g)/5.12g) = 3.91%
Red	3.81g	3.84g	100((3.84g - 3.81g)/3.81g) = .79%
Green	4.61g	4.39g	100((4.39g - 4.61g)/4.61g) = -4.77%
Brown	4.86g	5.22g	100((5.22g - 4.86g)/4.86g) = 7.41%
Yellow	5.15g	4.86g	100((4.86g - 5.15g)/5.15g) = -5.63%
Blue	5.52g	5.47g	100((5.47g - 5.52g)/5.52g) = -.91%

We had about an even number of positive and negative changes in mass, with the clear, red and brown solutions causing an increase in mass (g) while the green, yellow and blue solutions cause a decrease in mass (g).

Turnip Molarities

Color of Solution	% Change	Molarity
Brown	7.41%	dH2O
Clear	3.91%	.2M
Red	.79%	.4M
Blue	-.91%	.6M
Green	-4.77%	.8M
Yellow	-5.63%	1.0M

The molarities of the concentrations are recorded here in this data table. The molarities of the sucrose concentrations were determined by the solute potential equation. A noticeable trend is seen here, where the higher the molarity, the smaller the cell increases (initially)/the smaller the cell gets (after .4M).

Extent of Diffusion (%)

Surface Area and Volume Ratio

Cube Size (l, w, the height of each side = cm)	Surface Area (cm2)	Volume (cm3)	Surface Area/Volume Ratio (cm2:cm3)	Extent of Diffusion (%)
1cmx1cmx1cm	6cm2	1cm3	6cm2:1m3	87.5%
2cmx2cmx2cm	24cm2	8cm3	3cm2:1m3	57.8%
3cmx3cmx3cm	54cm2	27cmcm3	2cm2:1m3	42.1%

As shown here, the extent of diffusion is recorded. A trend is evident here: the bigger the cell size, the less diffusion takes place. As the cell size increases, the amount of diffusion that takes place decreases as more energy is required for diffusion to take place, making the process of diffusion longer.

Conclusion

These two experiments showed to us on a small scale something very complicated on the microlevel. The turnip experiment showed cells' responses to different environments. In our turnip experiment, we were able to find a significant trend: As the molarity increases, the cell size decreased. The cells, initially, were increasing less (dH₂O --> 7.41%, then .2M --> 3.91%), but the cells did increase in mass as the cells were placed in a hypotonic solution. The sucrose solution surrounding the turnip core diffused inside of the cells in order to achieve equilibrium. Eventually, as the molarity increased, the turnip core began to shrink (.4M --> .79%, then .6M --> -.91%). This is because the water inside the turnip core began to diffuse out of the cell and into the sucrose solution, which decreased the size of the turnip cores because the cell was placed in a hypertonic solution. This experiment demonstrates what occurs inside our bodies, where a cell performs osmoregulation (maintains fluidity balance in the organism, as mentioned in Chen, 2019). In the cell size experiment, a significant trend was found as well: As the surface area decrease, the rate of diffusion increased. In the 1cmx1cmx1cm agar cube, the rate of diffusion was 29.7% faster than the rate of diffusion in the 2cmx2cmx2cm agar cube, in which the rate of diffusion for the 2cmx2cmx2cm agar cube was 25.7% faster than the rate of diffusion for the 3cmx3cmx3cm agar cube. The reason that this trend exists is that as the cell gets bigger, it takes diffusion a lot longer to take place.

Analysis Questions

1. The agar cube with the size of 1cmx1cm1xcm had the highest extent of diffusion ([percent]), the agar cube with the size of 2cmx2cmx2cm had the second-highest extent of diffusion ([percent]) and the agar cube with the size of 3cmx3cmx3cm had the lowest extent of diffusion ([percent]).
2. A trend is evident in this investigation: The smaller the cell (the surface area to volume ratio), the higher the extent of diffusion was.
3. The relationship between the cell volume and extent of diffusion is positive, so the higher the cell volume, the higher the extent of diffusion.
4. The relationship between the cell surface area and extent of diffusion is inverse, so the higher the cell surface area, the lower the extent of diffusion.
5. If cells were to get really big, then the cell would not be able to perform homeostasis. Homeostasis is crucial for the maintenance of a cell.
6. The cell can get small enough to increase the rate of diffusion adequately, but not too small so that the fast rate of diffusion causes the cell to become unstable or damaged. On the other hand, the cell can get big enough to slow down the rate of diffusion when needed, but it cannot get too big or else the cell will not be able to reap the benefits of diffusion.

References

• Palaparthi, Sarvani. “Role of Homeostasis in Human Physiology: A Review.” Omicsonline, Journal of Medical Physiology & Therapeutics, 2017, www.omicsonline.org/open-access/role-of-homeostasis-in-human-physiology-a-review.pdf.
• Chen, Jiatong (Steven). “Physiology, Osmoregulation and Excretion.” StatPearls [Internet]., U.S. National Library of Medicine, 30 Apr. 2019, www.ncbi.nlm.nih.gov/books/NBK541108/.