A chicken egg, although very large, is actually just one cell. If placed in vinegar for three days, the calcium in the hard shell dissolves. The remains of the egg is surrounded by a soft and selectively permeable (only allows certain molecules to come and go) membrane which works as a compartment, separating the internal from the external environment (BSCS 1997)
An onion skin is made up of many cells, which are surrounded by a cell wall. The membranes of these cells and the cell wall are also compartments that form boundaries between the inside and outside environments. (BSCS 1997)
In this lab activity, we explored two concepts: homeostasis, the tendency of an organism to maintain a stable and constant internal environment; and osmosis, the movement of water across a selectively permeable membrane. By using two different types of cells, a chicken egg and cells in a piece of onion skin, we were able to understand the two concepts of osmosis and homeostasis better. We placed the cells into different environments and observed how they responded. Our main question was: How will the cells maintain homeostasis in these new environments? By using the knowledge we attained by doing our homework and reading the section on molecular movement (BSCS 1997), we hypothesized that the cells would expand when placed in an environment with high water concentration, and shrink in an environment with low water concentration.
We began the experiment by soaking three eggs in vinegar for three days to remove the shells. We did this by placing the eggs in a bowel, covering them with vinegar, and wrapped the bowl loosely in plastic wrap. The acid in the vinegar dissolved the calcium carbonate in the shells. After 24 hours, we removed the eggs from the bowl of old vinegar and replaced it with fresh vinegar. This we repeated on the third day. The next day, Monday, we brought the eggs to school and ran them under water, carefully removing any excess...