Page 90 - NCERT Science Class 10 English Medium

Activity
Activity 5.35.3
Activity
5.3
Activity 5.3
Activity 5.3
n Take 1 mL starch solution (1%) in two test tubes (A and B).
n Add 1 mL saliva to test tube A and leave both test tubes undisturbed
for 20-30 minutes.
n Now add a few drops of dilute iodine solution to the test tubes.
n In which test tube do you observe a colour change?
n What does this indicate about the presence or absence of starch
in the two test tubes?
n What does this tell us about the action of saliva on starch?

We eat various types of food which has to pass through the same
digestive tract. Naturally the food has to be processed to generate
particles which are small and of the same texture. This is achieved by
crushing the food with our teeth. Since the lining of the canal is soft, the
food is also wetted to make its passage smooth. When we eat something
we like, our mouth ‘waters’. This is actually not only water, but a fluid
called saliva secreted by the salivary glands. Another aspect of the food
we ingest is its complex nature. If it is to be absorbed from the alimentary
canal, it has to be broken into smaller molecules. This is done with the
help of biological catalysts called
enzymes. The saliva contains an
enzyme called salivary amylase that
breaks down starch which is a complex
molecule to give simple sugar. The food
is mixed thoroughly with saliva and
moved around the mouth while
chewing by the muscular tongue.
It is necessary to move the food in
a regulated manner along the digestive
tube so that it can be processed
properly in each part. The lining of
canal has muscles that contract
rhythmically in order to push the food
forward. These peristaltic movements
occur all along the gut.
From the mouth, the food is taken
to the stomach through the food-pipe
or oesophagus. The stomach is a large
organ which expands when food
enters it. The muscular walls of the
stomach help in mixing the food
Figure 5.65.6
Figure 5.6 Human alimentary canal
Figure 5.6
Figure
Figure 5.6
thoroughly with more digestive juices.
The digestion in stomach is taken
care of by the gastric glands present in the wall of the stomach. These
release hydrochloric acid, a protein digesting enzyme called pepsin,
and mucus. The hydrochloric acid creates an acidic medium which
facilitates the action of the enzyme pepsin. What other function do you
think is served by the acid? The mucus protects the inner lining of the
stomach from the action of the acid under normal conditions. We

Life Processes 85

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