Diffusion Across a Semipermeable Membrane in Relation to Digestion
Semipermeable membranes are designed to allow the passage of certain sized, or smaller molecules, from a concentrated area to a less concentrated area but larger molecules. This process is utilized in the digestion of foods, the intestinal walls serve as a semipermeable membrane which allow the water to move freely across while proteins and larger particles require active transport. To demonstrate this concept, dialysis tubing was used to simulate the intestines of a caterpillar.
During this exercise, two beakers of water and Lugol’s were set up to demonstrate a cell membrane and two dialysis tubes were filled both with starch, and one with amylase. The starch is used to replicate the starch intake from the plants the caterpillar ingests. Since sugars are insoluble, plants convert them to starches to store them. In the first setup, where no amylase is present, there is no passage of starch from the inside of the tubing to the beaker, however, the Lugols is demonstrated to be a small enough molecule to travel across the membrane, demonstrated by the color change of the inside of the tubing from a cloudy white to a dark blue, a sign of reaction between the Lugol and starch. Once the caterpillar eats the starches, the digestive enzyme amylase breaks down the starch into the original, insoluble sugar. The sugar molecule is now small enough to travel across the membrane to the less concentrated area. This is demonstrated by the use of glucose strips to test the sugar levels both inside the tube and in the beaker. In this set up, the contents of the tubing did not turn a dark blue, demonstrating that all of the starch was broken down by the amylase.
When analyzing the glucose reading, the levels of glucose were higher on the inside of the bag than in the beaker. The glucose molecules are small enough to permeate the membrane, however they are still so large that it does not happen as quickly as water....