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. 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 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 sugar (Kayro) syrup. Day 4 – The eggs were removed from the 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.
Solution
type Egg initial
mass (g) Egg mass 24 hours
in solution (g) Observations
Vinegar 45 86 Shell disappeared
Egg appeared swollen
10% salt water 86 86 No change in egg
Kayro syrup 86 41 Egg is shriveled up,
much smaller
Blue distilled water 41 86 Egg is blue
Wrinkles gone, egg
seems normal size
Graph comparing cells by day:
Click to Enlarge
According to the text, we might expect to find this egg in which solution?
A) egg in blue distilled water
B) egg in 10% salt water
C) egg in syrup
D) egg in vinegar
