Diffusion Laboratory

Diffusion Through a Membrane Part 1 Diffusion Through a Membrane

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.

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

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

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.

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.

Third drawing Water is moving out Water is moving out

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