Diffusion Through the Membrane State Lab

Selectively Permeable The cell membrane is selectively permeable because it only lets certain molecules pass through the membrane

Glucose, water, O2, CO2, amino acids, and other small molecules are permeable to the membrane Starch, proteins, and other LARGE molecules are NOT permeable to the membrane. They must be DIGESTED, or broken down.

What we used for the lab Dialysis Tubing – used to make a “cell” that will allow small particles to pass through and not large particles Glucose Solution – a simple sugar made of one small molecule of sugar Starch Solution – a complex carbohydrate made of hundreds of simple sugars bonded together

Indicators Starch Indicator Solution – (Iodine), a really small molecule (It’s only 2 atoms big) Glucose Indicator Solution – Benedict’s solution

The state lab was all about DIFFUSION!!!!!! We used an “artificial cell” to observe the movement of glucose, starch, and starch indicator.

AMBER WHITE

An indicator is used to test for the presence of a chemical substance. Starch indicator (iodine) is amber brown. It will turn blue/black in the presence of starch. The beaker was LEFT ALONE for 20 minutes After 20 minutes, the bag turned black, the beaker stayed amber

What Happened?? Glucose was small enough to pass through the membrane so it ended up in the water outside the cell Starch was too big to pass through the membrane so it didn’t get out of the cell Iodine (starch indicator solution) was small enough to pass through the membrane so it ended up in the cell turning the cell blue-black

AMBER AMBER BLACK WHITE

The bag turning black told us that starch indicator (iodine) moved into the cell. The water staying amber told us that starch DID NOT move out of the cell.

But what about glucose?....

But what about glucose?.... In order to determine if glucose moved, a glucose indicator test had to be performed. Glucose indicator is clear blue, and IT MUST BE HEATED. Glucose indicator will turn red, yellow, or green (traffic light colors) if glucose is present.

A sample of the amber water was taken from the beaker and heated with glucose indicator. The test was POSITIVE. Glucose WAS present in the beaker.

I I I S G G G S S G S I I I I

I I G I I I G S G G I S G G S S S G S G G S S S I I I I I G I

Conclusion of the Lab Glucose and starch indicator were PERMEABLE to the dialysis tube membrane. Starch was NOT permeable to the membrane.