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Exercises

10 The digestion of lactose

Lactose, the milk sugar, is digested in the presence of an enzyme called lactase. Some children
suffer, since birth, from a digestive trouble due to the absence of lactase.
We give milk to two children A and B. Then, we measure the lactose concentration in certain
digestive organs in each child. The results of the measurements are shown in the document below.

Concentration of lactose in % Concentration of lactose in %
in child A in child B
100 100

50 50

25 Organs
of the
0 0 digestive
Organs tube
of the
digestive O
Esophagus Esophagus
tube
Mouth Stomach Small intestine Mouth Stomach Small intestine

a- Represent in the same table the different values of the lactose concentration in each digestive
organ in the two children A and B.
b- Analyze the results. What do you deduce? Lebanese Brevet 2006

11 The mechanical digestion

The mastication of food leads to its reduction into small pieces. A student wonders if this
mastication facilitates the chemical digestion of food in the presence of digestive juices such as
pancreatic juice.
To solve this problem, he performs an experiment in vitro showing the digestion of 50 grams of
fish. The conditions of this experiment and the results obtained are shown in the document below.

Conditions

Water Pancreatic juice Temperature in
50 g of fish in ml in ml ºC

Tube 1 in small pieces 5 1 37

Tube 2 in one large piece 5 1 37

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