In this lab, students will learn about the permeability of the cell membrane. By studying the ability of a shell-less egg to absorb various solutions, students can see how membranes can regulate a cell’s interaction with its environment.
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- A human cell has a protective layer called a cell membrane.
- The cell membrane is semi-permeable, meaning that some molecules easily move across the cell membrane, some cannot.
- When solutions containing different amounts of ingredients are separated by a semi-permeable membrane, diffusion of molecules occurs. Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. For example, diffusion can occur across biological membranes or down concentration gradients.
- There are 3 main types of diffusion:
- Passive Transport is when molecules diffuse without the use of energy from the cell, from areas of high amounts to areas of low amounts.
- Active Transport is when molecules diffuse with the use of energy from the cell (and a special pump), from areas of low amounts to areas of high amounts.
- Facilitated Transport is when molecules diffuse from areas of high amounts to areas of low amounts without the use of energy from the cell, but with the help of proteins that form channels across the cell membrane. Remember that to facilitate means to “help,” so sometimes molecules need help getting across the cell membrane and special proteins facilitate this!
- Graduated Cylinder (or 25mL beaker)
- Plastic Sandwich Bag
- Twist Tie
- 500mL Beaker or Flask
- Iodine Solution
- Liquid Starch
- 3 chicken eggs with shells dissolved by vinegar
- White vinegar
- 3 clear plastic cups
- Light Corn Syrup (enough to completely cover eggs)
- Liquid egg whites (enough to completely cover eggs)
- Distilled Water (enough to completely cover eggs)
- Triple-beam balance OR Rudimentary scale with jelly belly beans [consists of 2 sandwich bags, 3 pieces of string, and one 3-hole punched ruler, and a pack of jelly beans]. If scale is unavailable, only measure circumference.