1. Diffusion Laboratory

2. Diffusion Through a Membrane
Part 1
Diffusion Through a Membrane

3. Lugols iodine solution is placed in the beaker
Initial State
The bag is tied off
Lugols iodine solution is placed in the beaker
A starch and glucose solution is placed in a plastic bag I S G
The bag is placed in the beaker
Lugols iodine solution is naturally a golden brown color. It turns a bluish black color when starch is added.

4. After sitting for 20 minutes
Final State
After sitting for 20 minutes I I S I S S I I I S I S I S
Note the color changes in the bag and the beaker from the initial state

5. Diffusion of Water Across a Membrane (Osmosis)
Part 2
Diffusion of Water Across a Membrane (Osmosis)

6. First drawing
Cell membrane
Cell wall
cytoplasm
These are cells from a red onion. They are suspended in distilled (pure) water, which is greater in concentration on the outside than the inside of the onion cell. The nuclei are prominent in the bottom cells, and the nucleoli are visible as dark areas inside the nucleus. In the cells at the top of the picture, the red pigment fills the cytoplasm, and internal structures aren't as visible.
Since the outside fluid has a greater concentration of water than the inside of the cell, water tends to flow into the cell, and the cell membrane completely fills the cell wall.

7. Second drawing
Cell membrane
cytoplasm
Cell wall
These are also cells from a red onion, but these are suspended in salt water, which is lesser in concentration of water to the inside of the cell. Water flows out from the cytoplasm, which reduces the volume of the cytoplasm. Like a balloon deflating inside a box, the plasma membrane pulls back from the cell wall in a process called plasmolysis.

8. Third drawing
Water is moving out
Water is moving out

9. Concepts You Must Know The dialysis bag is the "cell"
Diffusion moves material from high to low concentration, spending no energy
Only small molecules will go through the membrane...(starch can not)
Benedict's solution tests for sugar...heat it and it turns red (positive for glucose)
Iodine or Lugol’s solution tests for starch...turns blue / black in starch
Water is used as a control for the indicators
The diffusion of water is osmosis
The dialysis plastic "cell".... represents cell membrane
Iodine (starch indicator) is in water in beaker (outside the cell)
The "cell" should turn blue/black indicating that the iodine diffused into the "cell" and detected the presence of starch inside the "cell'
Test the water outside the "cell" for glucose...Benedict's will turn red after heating if it detects the presence of glucose outside the "cell'.
Starch WILL NOT diffuse out of the cell because it is too big and not permeable