A student investigates the digestion and absorption of proteins using a Visking tubing model to represent the small intestine.
Visking tubing is a selectively permeable membrane that allows small molecules (such as amino acids) to pass through, but prevents large molecules (such as proteins and polypeptides) from crossing. The distilled water in the boiling tube represents the bloodstream, and the Visking tubing bag represents the gut.
The student places different combinations of protein and active enzymes into the bag. After 30 minutes, they test the surrounding water for the presence of protein and free amino acids.
Complete the table below to predict the results (using yes or no) for each combination.
| Solutions in bag | Protein present in water | Amino acids present in water |
|---|---|---|
| protein only | no | no |
| protein and active pepsin | ||
| protein and active exopeptidase | ||
| protein, active pepsin, and active exopeptidase |
Explain how and why the mass of the Visking tubing bag would change if it initially contains a concentrated protein solution and is left in a boiling tube of pure water.
Describe the chemical test the student should use to detect the presence of protein in the water.
Explain how the student could use this model to investigate the effect of pH on the rate of protein digestion by these enzymes.