Egg Lab

Since it is difficult to see when osmosis is happening in cells due to the small size, in my science class we simulated what happens in a cell by using an egg. The egg may not be a single cell though; its membrane is selectively permeable, being a good model to show some basic osmotic effects in animal tissue.  Our aim was to investigate the effect of different solutions on an egg´s mass and volume.  For this experiment the class was split into groups of three. My group chose to use alcohol and salty water 20% solution. The goal of our experiment is to investigate the effect of different solutions on an egg´s mass and volume. At the beginning of the investigation, my group was asked to predict the possible effect. We predicted both eggs, either submerged in salty water 20% solution or alcohol, were going to dehydrate.

Before even starting the egg lab, all eggs spent two days in vinegar in order for the shells to dissolve. After the egg had no shell, my group was free to start the experiment. We measure each of the eggs mass, circumference, and solution filling each cup where the eggs were going to be submerged. Though, how were we going to differ each the second day? We named both eggs! The one in alcohol was named Stuart and the egg in salty water 20% solution, Steven. On the second and third day, we performed the same procedure: measuring the mass, circumference, and solution that was left inside cup from each egg. The average from my results and another group are recorded below. 

Average of Alcohol Solution Effects

Average of Salty Water 20%  Effects

Observations:

- the egg in alcohol got more yellow and lighter each day

- the egg in salty water 20% solution got whiter and heavier each day

- remaining solution decreased in both cups 

-when the egg in alcohol was opened, it looked like a boiled egg

- when the egg in salty water was opened, it exploded and scattered with a single touch

Conclusion and Analysis:

At the end of the experiment, my group had to summarize and analyze the experiment with our knowledge of osmosis. For the egg submerged in alcohol we concluded that there was a larger amount of water inside the egg than outside. This is when osmosis shows up. Since there was a higher concentration of water inside the egg, some H2O molecules went outside to keep balance. The reason the egg got smaller because it lost liquid. Though, how could the remaining solution in the cup be less if water was added to the total of 80ml (already outside the egg). Actually, alcohol evaporates really fast, a possible reason the remaining amount of alcohol reduced from 80ml to 68.5 and eventually until 59ml. At the end, our prediction was right, the egg did dehydrate since it got small and had a dry texture. 

On the other hand, the egg in salty water 20% solution, didn´t meet our expectations. My group thought it was going to dehydrate, supposed to decrease in mass and circumference. Though, the results were totally the opposite: the egg got heavier and larger. As a whole, my group concluded this happened due to the possible lower amount of water inside the cell, which lets the outside environment to send water particles to the inside of the cell. This reflects the enlargement of the egg since it was full of water. The most noticeable part where this effect happened is from the abrupt reduction of solution outside the egg between day 1 and day 2. It decreased from 80ml (what we started with) to 67ml. 

Possible Sources of Errors:


-Procedure: Pouring different amounts of the chosen solution. This may have been one of the causes why results varied a lot. Some groups submerged their eggs in a total of 100ml from their solution. Though, the cups where the eggs were being placed had a small space for the egg to fit. This didn´t let enough space for the primarily requested 100ml of solution. As a result, some of the liquid spilled due to the lack of room. The reason groups ended with various amounts of liquid, affecting the average. 
-Equipment:

String used to measure the eggs´ circumference could be easily stretched. Instead, a retractable tape measure could´ve been used. While you surround the tape around the egg, at the same time you are measuring the circumference. Helping you save some time. 

What have I learned?

Sincerely, the experiment was not a way of studying osmosis yet to review it. Osmosis is the movement of water molecules from a high concentrated area to low. This reflects what happened in the experiment. The center of the egg (yolk) contains protein and water. While, let´s say salty water contains salt and water. Osmosis may happen due to the fact that there are more water molecules in the yolk than in the solution (salty water). So, eventually water molecules move from the inside to the outside to keep balance. 

Team Evaluation:


In my opinion, my team worked efficiently all classes. While one member measured the circumference from one of the eggs, the other measured the mass from the other egg, while I placed the remaining liquid from the cup in the graduated cylinder to measure the solution that was left. We never got distracted by others. I very much appreciated the help from my group since it contributed in my understanding of osmosis. 

Cell Membrane

The simple facts students normally study about the cell membrane is that it´s made of fat and used for protection. If we were to see from a molecules´ point of view, what would happen inside the cell membrane? Actually, if we get through the cell membrane since it is selectively permeable, we could go through by either passive or active transport.   Through passive transport, substance can cross the cell membrane without using cellular energy. In other words, the cell doesn´t need to use its own energy.  On the other hand, active transport requires the cell to use its own energy in order to get through the cell membrane. Below, there´s an informative video I found which explains more clearly what I roughly explained.