Osmosis Lab Intro
This is Owen, Brendan, Erik, and James's Osmosis Lab. Here we'll explain every aspect of our 3 experiments, including our
materials, methods, results, and observations. Finally, we'll discuss our results.
Questions Posed
1) "What is the relationship between SA/V ratio and the rate of diffusion?"
2) "When the rate of diffusion for some solutions and those solutions' concentrations are plotted, is the trend linear or curved?"
3) "What % sucrose are the colored mystery solutions (answer is based on the data we collect from the yams' weight differences)?"
The answers to these questions are important because:
1) they enable us to identify the rate of diffusion for various sa/v ratios
2) they let us find the diffusion rate of various concentrations of sucrose thru dialysis tubing, and
3) they enable us to identify the unknown substances
Scientific Background
Diffusion is molecules' movement from a high concentration area to a low concentration area. Thus: a higher diffusion rate = more molecules going from one area to another.
Osmosis is the movement of a solvent (as water) through a semipermeable membrane (as of a living cell) into a solution of higher solute concentration that tends to equalize the concentrations of solute on the two sides of the membrane.
In our 1st lab, we cut fake "cells" and placed them in NaOH, after which we placed them in an HCl solution, recording "cell" weights throught. In our 2nd lab, we put various %s of sucrose in dialysis-tubing "cells" in order to find if the rate of diffusion was curved or linear. In our 3rd lab, we placed yams in unknown substances as well as a sucrose solution in order to find out which one had which % of sucrose.
Hypotheses
1) We hypothesized that the higher the SA/V ratio, the higher the rate of diffusion will be.
2) We hypothesized that as the % of the cell's soln. that is sucrose increases, the rate of diffusion will increase linearly.
3) We hypothesized that the yams will gain some mass, but the amount gained will vary.
Predictions
1) If a cell has a high SA/V ratio, then diffusion will occur at a high rate in that cell.
2) If a large portion of an artificial cell's solution is sucrose, then the rate of diffusion will be higher, and this will increase linearly.
3) If a yam is placed one of the unknown colored substances given to us by Mr. H, it will gain mass.
Materials and Methods
Procedure 1 - SA and Cell Size
1) Start by cutting variable length cells out of agar using a scapel. They should all be .5cm in radius. Then make one cell .5cm high, another cell 1cm high, and the third 2cm high.
2) Use the surface area formula and the volume formula to find the surface area and volume of each of the agar “cells”. Record the answers.
3) Find the SA/V ratio by dividing the surface area by the volume.
4) Place all of the “cells” into an NaOH solution for five minutes. They will be a deep pink all the way through.
5) Remove the cells from the NaOH solution and place them in a 50mL beaker
6) Cover the cells in a 1mol/L HCl solution inside the beaker
7) As soon as they are covered start three timers (one for each cell)
8) Watch the cells and stop the timer associated with each cell when they become clear all the way through
9) Record the times (in min/sec) and compare them to their respective SA/V ratios.
Formulas
Surface Area:
SA= d(pi)h+(pi(d)) (d is diameter, SA is surface Area and h is the height)
Volume:
V= ((pi(d/2))^2)h (d is the diameter, V is the volume and h is the height.
Surface Area to volume ratio
SA/V ratio= SA/V (SA is surface area and V is volume)
Procedure 2 - Modeling Diffusion and Osmosis
1) Start with six 20-cm long pieces of dialysis tubing
2) Tie off the ends of the tubes so that a solution could be poured inside
3) Into the first tied off dialysis tube put 10 mL of distilled water this will be the control
4) Into the second tube put 10mL of 20% sucrose solution (8mL distilled water and 2mL 1M sucrose) in the third a 40% solution ( 6mL distilled water and 4mL of 1M sucrose) continue adding sucrose solution in increments of 20% to the remaining tubes. The last one should be 100% 1M sucrose.
5) Tie these tubes off with string, creating an artificial cell
6) Fill six beakers each with 40 mL of distilled water
7) Mass the beakers and cells and record the results
8) Place a cell in each of the beakers for 15 minutes
9) Carefully remove the cells from the HCl and mass the cells
10) Mass the beakers
11) Find the change in beaker mass and the change in cell mass and record this
Procedure 3 - Osmosis In Live Cells
Yams served as the plant tissues (the solution diffused into it).
1) Fill 7 50ml beakers with 7 different solutions - Orange, Green, Blue, Yellow, Red, Pure Distilled Water, 1m Sucrose
2) We hollowed out cores of yam that were 1.5 grams +/-.15 and had a diameter of 1 cm. and set them into the 7 different solutions.
The first 5 solutions were mystery colored solutions that we knew contained a mix of sucrose and dist. water. The solutions were marked by their color (Yellow, Orange, Red, Blue, & Green.)
The last 2 were controls.
3) The yams were left for 23 hours in the solutions. The masses of the cups as well as each individual yam were taken before and after the immersion of the yam cores.
We compared the distilled water times with the 100% 1M sucrose solution in order to approximate the concentrations of the unknown solutions.
4) We compared the distilled water times with the 100% 1M sucrose solution in order to approximate the concentrations of the unknown solutions.
To find the % sucrose solution, then you first must think: if you have a 30% sucrose solution, then you also have a 70% distilled water solution.
5) Then you can say that if .15 grams of sucrose move in 100% sucrose, and .39 grams of movement in the 100% distilled water solution, then you can take the percent of each in the solution and add those movements together to get your total movement. (ex. a solution of 40% sucrose would be also 60% distilled water.)
6) Next multiply the sucrose movement by the % sucrose (0.4*0.15) and the same thing for the distilled water (0.6*0.39).
7) Then add the totals (.06+.234) from these two operations to get the total movement (.294). To get percents of each solute, you do this exact process backwards.
Results and Obervations
Our 3 Graphs (1=top, 3=mid, 2=btm)
Data & Captions
It appears that the only lab without an outlying data point is the last lab. In the first lab, it appears that the second data point is off. In the second lab, it appears that the first data point is off. We corrected this in the second graph but not in the first. If all these data points are corrected, it appears that the first graph is trending downward linearly, that the second graph shows an upward linear trend, and that the third graph shows an increase in mass for all the yams.
You can view our data tables here: table 1, table 2, and table 3.
Discussion
Lab 1
The relationship between the SA/V ratio of an artificial cell and its rate of diffusion is that as the surface area to volume ratio becomes smaller, the rate of diffusion decreases.
However, this isn’t demonstrated clearly in our lab due to an unforeseen variable. That variable is the time our cells spent soaking in the bath of NaOH. The time spent in NaOH was vastly different for each cell. This creates an outlier in the data, making our 2nd cell take 23 min 36 seconds to diffuse completely, while the other two cells took 5 min and and 5 min 45 sec.
This is a rather big problem. Yet, if you go by logic alone, you can see that as the sa/v ratio decreases the rate of diffusion decreases. The reason that this would be is that if there is more sq. cm. of surface area to each cubic cm of volume, each square cm of surface area would only be "responsible" for the diffusion into a smaller area inside the cell.
The way to improve this procedure would be to redo the cell soaking time, making sure the time spent in the NaOH bath was equal between the cells.
Lab 2
The rate of diffusion is linear due to the fact that as the concentration of the solute decreases, the amount of solute that diffuses in a given time through the dialysis tubing decreases linearly. This is known as a direct relationship. For example, when a linear trendline is placed upon the graph, it is the closest trendline to the actual data. Also, the increments between our percentage of solute (0, 20, 40% etc.) solutions is regular, and the increments between the amount of change in the cell is also regular (about a 0.15 gram change) which agains proves the line linear. However, there was an error in our data that will be addressed below. This lab could have been improved by a better monitoring of how the dialysis tubing was tied off to form the cell to prevent cell failure, and the amount of liquid in the cells should have been measured better Errors- The third data point (40% sucrose solution) was extremely inaccurate due to a spill resulting in a 6 gram change in the beaker weight, which is extremely out of line with the rest of the data points. This is approximately an 11% loss of solution, which can not merely be explained by evaporation. The data point is an outlier. we replaced it by averaging the two data points next to it on the graph.
Lab 3
There were 5 mystery solutions containing a mix of sucrose and water, and two solutions used as control/comparing variables. We determined that the Yellow mix was 50% sucrose, the Orange was almost entirely sucrose (95%), the Blue was 70%, the Green 15%, and the distilled water obviously 0%. These should be correct due to the fact that they meet the requirements of the formula for obtaining the solution concentration. (ex. Green is 15%, and that goes through the formula stated in the methods and the formula says the green should have moved 0.345, which is extremely close to the 0.35 that it did move) In analyzing these results, however, the orange data point must be excluded because it is theoretically impossible to get according to our process. The differences in mass of the different beakers were probably partially due to the different percent sucrose in each solution.
Errors
-Each cup lost about .5 grams of total mass after 24 hours due to evaporation
-The change in yam mass for the orange solution was because of imprecise measuring of the solution into our beakers, distorting the data.
Improve
We should have been more careful in our measurements. Instead of directly pouring from an imprecise beaker, we should have used an accurate, precise graduated cylinder, reducing the chance of significant human error.
The End
Site Inspiration
nclud & @desandro
.net magazine
Swiss design
Metro principles
Credits
Owen: created website, intro, data tables, & graphs
Erik: worked on data table, discussion, & intro
James: worked on materials and methods, data table, etc.
Brendan: worked on discussion, data table
MIT licensed & open-source.