Osmosis (Elahe Jahani)

Title: Osmosis: The diffusion of water.

Principle(s) Investigated:

• The diffusion of water molecules across a selectively permeable membrane.
  • The difference between hypertonic, hypotonic, and isotonic solutions and their effect on cells.

Standards:

Performance Expectation:

HS-LS1-2. : Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms. [Clarification Statement: Emphasis is on functions at the organism system level such as nutrient uptake, water delivery, and organism movement in response to neural stimuli. An example of an interacting system could be an artery depending on the proper function of elastic tissue and smooth muscle to regulate and deliver the proper amount of blood within the circulatory system.] [Assessment Boundary: Assessment does not include interactions and functions at the molecular or chemical reaction level.]

Disciplinary Core Ideas:

LS1.A: Structure and Function : Multicellular organisms have a hierarchical structural organization, in which any one system is made up of numerous parts and is itself a component of the next level.

Science and Engineering Practices:

Developing and Using Models: Modeling in 9–12 builds on K–8 experiences and progresses to using, synthesizing, and developing models to predict and show relationships among variables between systems and their components in the natural and designed worlds.

Develop and use a model based on evidence to illustrate the relationships between systems or between components of a system.

Crosscutting concepts:

Systems and System Models: Models (e.g., physical, mathematical, computer models) can be used to simulate systems and interactions—including energy, matter, and information flows—within and between systems at different scales.

Materials:

• Digital scale
• At least 800 mL of Vinegar
• Four chicken eggs (only two eggs will be used in the procedure, the other two will be prepared incase an egg ruptures during the de-shelling process)
• 300 mL of Deionized water (DI water)
• 300 mL of Corn syrup
• Two 500 ml glass beakers
• One 1L glass beaker

Procedure:

1. Place the eggs in the 1L glass beaker and fill the beaker with vinegar until the eggs are submerged.
2. Soak the eggs in vinegar for 48 - 72 hours. The vinegar will dissolve the egg shells. You can replace the old vinegar with new vinegar to speed up the process.
3. After the vinegar has dissolved the egg shells, remove the eggs from the vinegar soaking beaker and gently rinse them off with water to remove any shell residue.
4. Weigh the two de-shelled eggs separately with a digital scale, and record their mass.
5. Add 300 mL of DI water to one of the 500 mL glass beakers and 300 mL of corn syrup to the other 500 mL glass beaker, and place a de-shelled egg in each.
6. After 24 hours, remove each egg from their respective beakers and record their mass with the digital scale.
7. Compare the mass of each egg before and after it was placed in each solution.
8. You can place the de-shelled eggs back into the solutions for another 24 hours to see if there were any further changes to their mass.

(You may soak multiple eggs to have more than one egg in each solution and more trials of this experiment.)

References:

Naked Eggs: Osmosis

Growing and Shrinking Eggs

Student prior knowledge:

Students should have a prior understanding of the concept of diffusion and that it is particles moving from an area of high concentration to low concentration.

Explanation:

Osmosis is the diffusion of water across a selectively permeable membrane. This experiment used a chicken egg to show the concept of osmosis by placing de-shelled chicken eggs in a hypertonic and a hypotonic solution. Once the shells of the eggs were dissolved with vinegar, it exposed the selectively permeable membrane of the chicken egg which only allows water and gases (such as oxygen and carbon dioxide) to pass through. Osmosis is the diffusion of water molecules from an area of low solute concentration to an area of high solute concentration. When cells are placed in a hypertonic solution, there are more solutes outside the cell than inside the cell. When cells are placed in a hypotonic solution, there are more solutes inside the cell than outside the cell. When cells are placed in an isotonic solution, there are an equal amount of solutes inside and outside the cell. The chicken egg placed in corn syrup was in a hypertonic solution, causing the water inside the egg to leave, lowering its mass and giving it a shriveled appearance. The chicken egg placed in DI water was in a hypotonic solution, causing the water outside the egg to come inside and increase its mass.

Questions & Answers:

Could you use different sugar solutions with different concentrations of corn syrup in the experiment?

Yes! You can prepare corn syrup solutions with different concentrations of sugar by diluting corn syrup with DI water. This will cause the eggs to shrink varying amounts.

Why don’t plant cells explode like animal cells when placed in a hypotonic solution when water enters the cell?

Plant cells have a cell wall made of cellulose around their cell membrane, which provides the cell structure and stops them from bursting open. When a plant cell is placed in a hypotonic solution it becomes turgid.

Why is understanding osmosis important to the human body?

Understanding osmosis is important to the human body because the water and cells in our body exist in an isotonic state. If a liquid is injected into our body (such as an IV solution), it has to have an isotonic concentration to the cells in our body. If the IV solution is hypertonic to our cells, our cells will shrivel, and if the IV solution is hypotonic to our cells, our cells will burst.

Applications to Everyday Life:

An example of osmosis occurring when cells are placed in a hypertonic solution in the real world is when salad dressing is added to chopped lettuce, other leafy greens, and vegetables in a salad. The salad dressing contains more solutes in it than the plant cells making up the lettuce, so the water in the lettuce cells exit leaving the salad looking wilted. That’s why it’s not good to pre-dress salad and leave it for a long period of time before eating.

Grocery stores often spray their produce with water or a solution that doesn’t contain a high percentage of solutes. This is an example of osmosis taking place when cells are put in a hypotonic solution, because the plant cells of the fruits and vegetables on display have more solutes inside their cells, it causes the water that’s being sprayed on them to enter their cells. This causes their cells to become turgid giving them a plump and fresh appearance and making them more appealing to shoppers.

An example of isotonic solutions at work in the real world is Ringer’s solution. Ringer’s solution is given as an IV treatment in clinics and hospitals to patients who are dehydrated. The Ringer’s solution has to be isotonic to human cells so it doesn’t cause our blood cells to shrivel or explode.

Photographs & Powerpoint:

Osmosis: the diffusion of water