Page 17 - exemple

The brick red precipitate appears in tube A only.
If we add acid (pH < 7) or a base (pH > 7), will starch be digested?
What is the appropriate pH for this digestion?
Document 7 represents the variation of the enzymatic activity in the digestive system as a function
of the pH. Each enzyme has an optimal activity at a specific pH.

Enzymatic activity in %

Pepsin Pancreatic and
Salivary
(gastric intestinal enzymes
amylase
enzyme)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH

Acidic medium Neutral medium Basic medium

Doc 7- Variation of the percentage of the enzymatic activity as a function of the pH.

2 Importance of temperature

To determine whether temperature
Cooked starch +
variation affects the enzymatic saliva + iodine
activity, scientists performed the water
following experiment.
Experiment: Pour in a beaker a A
solution of cooked starch and add 15 minutes later
fresh saliva to it.
Take two samples from the solution
No change in the
and put them in two test tubes (A) coloration
and (B).
1- Put test tube (A) in a beaker After 15 minutes
containing ice at 0°C.
15 minutes later, the dark blue B
coloration persists.
2- Put test tube (B) in a beaker 37ºC
containing water maintained at Change in the
coloration
37°C (normal body temperature).
The dark blue coloration Doc 8- Effect of the temperature on the enzymatic
disappears. activity.
3- Reput test tube (A) in a water bath at 37°C, the blue coloration disappears.

Digestion 21