Question

Diffusion of gases across a permeable membrane

1. How long did it take the O2 levels to become about equal outside and inside the cell? What happened to those levels after they became about equal over the additional 10 seconds? Why did this happen?

My answer: It took 6 seconds to become equal. After they became about equal over the additional 10 seconds they fluctuate back and forth as equal equilibrium is achieved.

2.Cell use O2 and produce CO2 as part of their metabolism. Using your observations from this simulation, describe how a cell gets the O2 the cell needs and gets rid of the CO2 that is doesn’t need and can actually be harmful to the cell.

Osmosis

	Treatment A Control	Treatment B 0% sugar	Treatment C 5% sugar	Treatment D 10% sugar	Treatment E 15% sugar
Beginning Weight in Grams
End Weight in Grams
Percent Weight Change

1. Which dialysis tubes had little or no change in the mass after the 24- hour period?
   1. “A”, “C”, “E”
   2. “C”, “D”
   3. “A”, “D”
2. Why was pure water used as a control group?
   1. The control group provides a standard for comparison for the experimental group.
   2. The control group represents a real cell because real cells contain water.
   3. The control group was not necessary.
3. Why didn’t the mass of dialysis tubes “A” and “D” change over the 24-hour time frame?
   1. The dialysis tubing material was clogged.
   2. The concentration both inside and outside the dialysis tube is the same.
   3. The pressure of the dialysis tubing membrane stabilizes the flow of water.
4. Which statement below best describes how a cell responds to its’ external environment?
   1. The difference in concentration of solids in a cell’s external environment has no effect on how water moves into and out of a cell.
   2. If the concentration of solids in the cell’s external environments is greater than the internal environment, water passes out of the cell.
   3. If the concentration of solids in the cell’s external environment is less than the internal environment, the water passes out of the cell.
5. This virtual experiment was conducted at room temperature, which is about 20°C, and ran for 24hours. Using your knowledge about diffusion from the previous exercises, would you raise or lower the temperature in order to get similar results in a shorter period of time? Using your knowledge from the previous exercises explain why your choice would work.

Answer 1

The oxygen enters the bloodstream from the alveoli, tiny sacs in the lungs where gas exchange takes place. The transfer of oxygen into the blood is through simple diffusion. A protein called hemoglobin in the red blood cells then carries the oxygen around your body. At the same time, carbon dioxide that is dissolved in the blood comes out of the capillaries back into the air sacs, ready to be breathed out. When oxygenated blood reaches muscle cells, the bond between oxygen and hemoglobin molecules loosens. When the red blood cells pass single file through the tiny capillaries that surround muscle cells, oxygen molecules are released from hemoglobin and diffuse into the muscle cells. The carbon dioxide produced by the muscle cells diffuses into the bloodstream not as CO2 but as bicarbonate ion (HCO3 −) that is converted back into CO2 in the lungs, where it is exhaled.