Background: Osmosis is the movement of water molecules across a cell membrane from high concentration to low concentration of a solute. To further understand the process of this element of passive transport and find differences between hypertonic, isotonic, and hypotonic solutions, an experiment will be done with eggs and solutions of different salt concentrations to further examine the process.
Decalcified eggs will be placed in different solutions (15% salt solution, 5% salt solution, and distilled water) and will be observed to see changes to the mass of the egg. The eggs will be weighed before the experiment and at 10 minute intervals. A decalcified egg is being used not to mimic a single cell, but to act as a semi-permiable membrane. The membrane of the egg will only allow certain materials through it.
Dependent variable: Mass of decalcified eggs
Constants: Temperature of water, amount of solution, type of egg, 250 ml beaker
Control: Distilled water
1. Gather materials
- Three decalcified eggs
- 150ml of each solution (distilled water, 5% salt, 15% salt)
- Three 250ml beaker
- Masking tape
- Weighing boats
2. Find mass of each egg before putting the egg in any of the solutions.
3. Put solutions in separate containers
4. Label each container according to the solution they contain
5. Distribute eggs into each solution (one egg for each solution)
6. Measure the weight of each egg every ten minutes, then put the eggs back into their previous containers (soak eggs for 40 minutes)
7. Record data
8. Calculate average mass change between each egg
Mass of eggs before experiment:
Distilled water egg: 76.47 grams
5% salt solution egg: 96.62 grams
15% salt solution egg : 84.68 grams
|Distilled water at 10 minutes||
||Mass: 78.02 grams|
|Distilled water at 20 minutes||
|Distilled water at 30 minutes||
|5% salt solution at 10 minutes||
|5% salt solution at 20 minutes||
|5% salt solution at 30 minutes||
|15% salt solution at 10 minutes||
||Mass: 84.58 grams|
|15% salt solution at 20 minutes||
|15% salt solution at 30 minutes||
Conclusion: The original proposition was that if an egg was placed into distilled water the mass would increase, if an egg was placed into a 5% salt solution the mass would remain the same, and if an egg is placed into a 15% salt solution the mass of the egg would decrease. The original hypothesis was supported. The mass of the distilled water egg increased, the mass of the 5% salt solution egg changed the least and the 15% salt solution decreased . The total change for the mass of each egg was:
Distilled water: +3.3 grams
5% salt solution: -.29 grams
15% salt solution: -.5 grams
The egg in the distilled water began to bulge and expand. The membrane ” stretched”. The liquid level decreased. Thus water diffused across the cell membrane and this solution was hypotonic. The egg placed into the 5% salt solution changed the least, thus the solution was isotonic to the egg. The liquid level did fluctuate but overall it stayed the same. The egg’s mass decreased when put into the final solution, the 15% salt solution. The 15% salt solution was hypertonic. The solution level increased slightly due to the water diffusing across the “membrane”.
Water moves from high concentration to low concentration. Because eggs do contain a slight amount of salt, water wanted to maintain dynamic equilibrium and caused the water to move in areas of high concentration to areas of low concentration. The distilled water was the hypotonic solution because it caused the eggs mass to increase and “bulge”. The 5% salt solution was the isotonic solution because the mass of the egg decreased the least meaning there was a constant movement of water through the cell membrane. The 15% salt solution was the hypertonic because it caused the eggs mass to decrease and “wrinkle”. This lab is an example of passive transport because osmosis is a type of passive transport. It required no energy and water molecules moved with the concentration gradient (high concentration to low concentration). Facilitated diffusion requires no energy and moves with the concentration gradient, just like osmosis in our experiment. Although, facilitated diffusion does require a protein, osmosis does not. Active transport requires a protein, moves against the concentration gradient, and it requires energy, the osmosis that occurred through the eggs did not require energy or a protein, and it did NOT move against the concentration gradient.
Our group conducted the experiment well, we discussed and came up with the data above, together we understood that osmosis is a type of passive transport that involves water molecules. Unfortunately, our experiment did have a few, but minor errors. First off, our group forgot to zero the scale on the first weigh of the eggs this did not give 100% accurate reading for the first weigh. Second, the containers and utensils were not completely clean when used. Some modifications could be to soak the eggs in different solutions such as vinegar, corn syrup, or lime juice. Also, the eggs did not have a large amount of time to soak in the solutions, thus not giving us the best results obtainable. Maybe leaving the eggs overnight or over a weekend would give us more accurate results.Osmosis occurs everywhere. Another example of osmosis besides in our experiment, is in the human body, osmosis plays a key role in the function of the kidneys. It also aids in transferring water and various nutrients through blood and fluid of cells. Osmosis happens in our bodies every day, but it also occurs in the medical field. If completely sterile water was given to patients who are dehydrated, the cells within the blood vessels would draw up all of the fluid because of the concentration gradient shift, this would cause the nearby cells to swell and rupture. This would mean that the red blood cells could no longer be able to move oxygen.