Tuesday, October 4, 2011
Today we had a quiz in everything we've learned so far in the cells unit. We read over and completed day 1 of the Egg Osmosis DEMO in class. Also we did the "Diffusion Through a Cell Membrane" lab. Due today was to read pages 37-39 in UP.
The Egg Osmosis DEMO
The Egg Osmosis Demo, found on pages 45-47 in the unit packet, talks about hows osmosis is the diffusion of water across a semi-permeable membrane. It also talks about homeostasis and how it is maintained in part by controlling the movement of materials into and out of the cell.
In class Mrs. Andrews held up an egg and we drew a picture of it and made observations like; white, hard shell, and oblong. This was recorded under day 1-raw egg on page 46 in the unit packet.
Diffusion Through a Cell Membrane Lab
1. We drew a diagram of what our materials will look like when they are set up. There is the dialysis tubing that
contains glucose, starch, and water that is placed in a beaker which contains 50mL of water and iodine (brownish yellow color).
2. We proceeded with the lab by adding glucose and starch to the tubing and tying it off then placing it in a beaker filled with iodine and water for 15 minutes.
3. After 15 minutes we came back and the starch in the tubing had turned a blue black color and settled to the bottom. Also the iodine diffused in the tubing because the liquid inside the tubing was a brownish yellow color.
4. By dipping a piece of Tes-Tape (glucose indicator paper) into the liquid in the beaker we found that there was a
presence of glucose outside the tubing because the tape turned a to light green. From this we
concluded that the glucose diffused from inside the dialysis tubing to the beaker.
After 15 minutes the beaker looked like this. With the starch dyed blue/black because of the iodine and iodine diffused into the tubing as well as the glucose diffused into the beaker although you cannot see it.
From these results we concluded that:
1. The iodine diffused from the high concentration in the beaker to the low concentration in the dialysis tubing.
2. The glucose diffused from the high concentration in the tubing to the low concentration on the beaker.
3. The water did a little bit of diffusing both into the tubing and out.
4. Starch molecules are a lot larger than glucose, water, and iodine molecules because they couldn't diffuse through the dialysis tubing membrane.
Due tomorrow is the Diffusion Through a Membrane lab (p.37-39)