Students performed an experiment using eggs to observe the effect of osmosis on cells. The egg represented a typical cell. Befor
e beginning the experiment, students soaked the raw eggs overnight in vinegar to remove the shells. What they had in hand, then, was actually a raw, shell-less egg. Osmosis is the movement of water from an area of greater to lower concentration through a semi-permeable membrane. Water moves in and out of cells without any expenditure of cellular energy. Solution concentration can be described in terms of tonicity. Solutions are hypertonic, isotonic, or hypotonic to cells. A hypertonic is one that has a greater concentration of solute outside the cell and therefore a lower concentration inside the cell. Water will leave the cell and move to the outside environment. This is one reason organisms that live in fresh water cannot survive in salt water, such as the ocean. Water will leave the organism’s cells and eventually the cells will undergo plasmolysis and the organisms will die. An isotonic solution is a balanced solution. That is, the solution concentration is balanced with the solution inside the cell. Finally, when a cell is surrounded by a hypotonic solution, concentration of solute is greater inside the cell, concentration of water is greater outside. Water moves into the cell and the cell swells. If enough water enters, the cell can burst.
Procedure: Day 1 – Students found the mass in grams of their shelled eggs, recoding the mass in the data table. The eggs were placed in a beaker and covered with 200 mL vinegar to remove the shells. Day 2 – The eggs were removed from the vinegar. Visual observations were recorded. The shell-less eggs were wiped dry, massed, and the mass was recorded in the data table. The eggs were placed in a clean beaker and covered with a 10% salt- water solution. Day 3 – The eggs were removed from the salt water and visual observations were made and recorded. The eggs were wiped dry , massed, and the mass was recorded. The eggs were placed in a clean beaker and covered with Kayro syrup. Day 4 – The eggs were removed from the Kayro syrup and visual observations were made and recorded. The eggs were carefully wiped with a damp cloth, massed, and the mass was recorded. The eggs were placed in a clean beaker and covered with colored (red, green, or blue) distilled water. Day 5 – The eggs were removed from the water and visual observations were made and recorded. The eggs were dried, massed, and the mass was recorded. Students organized their data and made a bar graph comparing how the solutions affected their egg's (cell’s) mass. Data: One student group’s data is recorded here.
The passage states that organisms that live in fresh water cannot survive in salt water. These organisms will undergo a process termed plasmolysis. An organism experiencing plasmolysis would resemble the egg subjected to which variable of the experiment?
