Osmosis - Naked Eggs (Lisa Hellinger)
Author:
Lisa Hellinger
Principle(s) Illustrated:
Osmosis, the diffusion of water from an area of higher water concentration to an area of lower water concentration is demonstrated using a shell-less chicken egg. With the shell removed students have the opportunity to see the effects of different solutions on a cell with a selectively permeable membrane. Eggs will be placed in water, a sugar solution and a salt solution. The concepts of hypertonic and hypotonic will be discussed.
Standards:
NGSS Science & Engineering Standards
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 how relationships among variables between systems and their components in the natural and designed worlds.
Develop a model based on evidence to illustrate the relationships between systems or components of a system. (HS-LS2-5)
Constructing Explanations and Designing Solutions
Constructing explanations and designing solutions in 9– 12 builds on K–8 experiences and progresses to explanations and designs that are supported by multiple and independent student-generated sources of evidence consistent with scientific ideas, principles, and theories.
Construct and revise an explanation based on valid and reliable evidence obtained from a variety of sources (including students’ own investigations, models, theories, simulations, peer review) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future. (HS-LS2-3)
NGSS Cross-cutting Concept Standards
Structure and Function
Investigating or designing new systems or structures requires a detailed examination of the properties of different materials, the structures of different components, and connections of components to reveal its function and/or solve a problem. (HS-LS1-1)
Systems and System Models
Models (e.g., physical, mathematical, computer models) can be used to simulate systems and interactions including energy, matter, and information flow - within and between systems at different scales. (HS-LS1-2), (HS-LS1-4)
Stability and Change
Much of science deals with constructing explanations of how things change and how they remain stable. (HS-LS2-6),(HS- LS2-7)
NGSS Disciplinary Core Idea Standards
Structure and Function
Systems of specialized cells within organisms help them perform the essential functions of life. (HS-LS1-1)
Questioning Script:
Prior knowledge & experience:
Solutes tend to move from an area of high concentration to an area of low concentration
Membranes are selectively permeable
Root question:
What happens to a shell-less egg that is placed in water, a salt solution, or a sugar solution?
What is the process that can explain what is observed?
Target response:
Eggs placed in water will get larger or gain mass because the concentration of water outside the cell is greater than inside the cell and the water from the jar moved into the egg.
Eggs placed in a salt solution will get smaller or lose mass because the concentration of water outside the cell is less than inside the cell and the water from the egg moved into the jar.
Eggs placed in a sugar solution will get smaller, lose mass because the concentration of water outside the cell is less than inside the cell and the water from the egg moved into the jar.
Common Misconceptions:
All cells are microscopic
Diffusion and osmosis do not occur across nonliving membranes
Egg shells or cell walls are substitutes for cell membranes
Water doesn't move along a concentration gradient only solutes do
Materials & Procedures:
Materials:
4 Raw eggs with shells removed
250 ml of vinegar in sealed mason jar
250 ml of water in sealed mason jar
250 ml of corn syrup in sealed mason jar
250 ml of salt water in sealed mason jar
Plastic spoons
Paper towels
Balance
Procedures:
Remove Shells (Start 2 days before activity)
Replace with fresh vinegar every 24 hours until shell is completely dissolved
Allow students to handle eggs and write down observations
Note initial mass of each shell-less egg
Assign a team of students to each jar
Place one egg in each mason jar
Teams time lapse video to document event
Teams write down observations
Note final mass of each egg
Discuss students' explanations
Other Variations:
What is happening when the egg is placed in vinegar?
The reaction is: CaCO3+ 2H+ -> Ca+2 + H2O +CO2
The shell composed of calcium carbonate is dissolved.
The bubbles observed are the release of carbon dioxide gas. (Students will think it is oxygen.)
Photographs and Movies:
Egg shell dissolving in vinegar.
Shell-less egg in water Shell-less egg in corn syrup
(hypotonic solution) (hypertonic solution)
Left egg after gaining water from soaking in water.
Right egg after losing water from soaking in corn syrup.