Page 11 - exemple

Exercises

1 Exploit the experimental results

When we chew bread crumbs for a long period of time 1 2
in our mouth and mix it with saliva, we perceive a
modification of the crumbs’ flavor that becomes slightly Cooked Cooked
starch + starch
sweet. Bread contains a complex sugar, starch. We fresh
think that starch was transformed into another sugar in saliva
the presence of saliva. To verify this hypothesis, 37ºC
scientists performed an experiment, whose conditions
After 30 minutes
and results are represented in the adjacent document.
a- Copy and complete the table.

Tube 1 Tube 2 1 2

Aspect of the tube at the
Whitish
beginning of the experiment
Aspect after 30
minutes

b- After 30 minutes, when applying the Fehling test to a sample taken from each tube, only tube
1 shows positive results.

c- Specify the role of tube 2.
d- Define the term «reducing sugar».
e- Analyse the results of the experiment.
f- Describe a test that allows us to confirm the absence of starch in tube 1 after 30 minutes.
g- Is the formulated hypothesis validated ? Justify the answer.

2 Chemical
composition of
certain foodstuffs

Water
Draw a table to classify the
following food items into Meat Egg Milk Fish (saumon)
three groups; those that are
Proteins
rich in proteins, rich in lipids
and those rich in
carbohydrates. Lipids

Cheese Butter Bread Beans (grain)
(gruyère)
Carbo-
hydrates

Mineral
salts
Potato Carrot Nuts Apple

Food 15