A student investigates the absorption of digested nutrients from the digestive tract using a Visking tubing model.
Visking tubing is a selectively permeable membrane that allows small molecules (such as monomeric amino acids) to pass through but prevents large polymers (such as proteins) and intermediate polypeptides from crossing. The distilled water in the beaker represents blood, and the Visking tubing bag represents the gut.
The student places different active enzyme and substrate combinations into the bag. After 20 minutes, they test the surrounding water for the presence of protein and amino acids.
Complete the table below to predict the results (using yes or no) for each combination.
| Solutions in Visking tubing bag | Protein present in outer water | Amino acids present in outer water |
|---|---|---|
| Protein only | no | no |
| Protein and active protease | ||
| Protein and active peptidase | ||
| Protein, active protease, and active peptidase |
Explain how and why the volume of the Visking tubing bag would change if it initially contains a concentrated protein solution and is left in a beaker of distilled water.
Describe the chemical test the student should use to detect the presence of protein in the outer water.
Explain how the student could use this model to investigate the effect of pH on the rate of protein digestion by protease.