Digestion, Let’s Break if
Down Before Lunch!
Presented by: Jana Causey
Objectives:

To introduce some fun experiments that
teach the principles of digestion

Offer alternatives and augmentations to
experiments that will revitalize your
digestion lab

Simplify and reduce costs
Lets Get Started:
6 test tubes total, but today each group
has 2
 Label each tube:

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L (Lipase)
LC (Lipase control)
P (Pepsin)
PC (Pepsin control)
A (Amylase)
AC (Amylase control)
Lipase
Place 10 drops of milk into both tubes
 Place 1 drop of phenol red into both test
tubes
 Place 1 drop of soap into both test tubes
 Place 5 drops of Lipase into the test tube
labeled L. No enzyme goes into the test
tube labeled LC.
 Swirl test tubes and place test tubes in hot
water bath.

Pepsin
Place 10 drops of albumin (component of
egg white) into both test tubes.
 Place 10 drops of biuret into both test
tubes.
 Place 5 drops of pepsin into the test tube
labeled P. NO enzyme goes into the test
tube labeled PC.
 Place test tubes in hot bath for 45 min.

Salivary Amylase/Diastase
Place 10 drops of diastase into tube
labeled A. Do not put enzyme into the
test tube labeled AC.
 Place 10 drops of starch solution into both
test tubes (same amount in both tubes).
 Place 10 drops of Benedict’s reagent into
each of the two test tubes.
 Place test tubes in hot bath for about 20
min.
 Test tubes will need to be boiled for 2 min.

Background

Digestion begins in the mouth
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Mechanical and chemical
Salivary amylase breaks down starch into
sugars
Benedict’s reagent is an indicator of reducing
sugars
Background
When food is swallowed and
Reaches the stomach, chief
Cells release pepsinogen
which is activated to pepsin
by the HCl acid released by
The parietal cells. The pH is
Approx. 2.

stomach
Background
The presence of food stimulates peristalsis
of the smooth muscle and the food is
pushed through the digestive system
 When the food enters the duodenum, the
pancreas will release pancreatic juice with
a pH of about 8 and it includes lipase,
proteases, and amylase.
 Also, the liver makes bile which is stored
in the gall bladder. Bile salts act as an
emulsifier which allows the fats to absorb.

Indicators
Phenol red indicator- The pH range is
from 6.8-8. Fats are neutral until they
brake down into fatty acids and glycerol.
The release of fatty acids will lower the pH
and the color will turn from red to orange.
 Biuret- A purple color appears in the
presence of protein. As the protein breaks
down into amino acids, the purple turns
brown

Indicators cont.

Benedict’s reagent- A precipitate will
form and the light blue color will change in
the presence of reducing sugars. Cu+2
reduced to Cu+ which precipitates to form
red copper (I) oxide, so the blue color
disappears.

Soap acts as bile and is added to the
lipase to allow for emulsification.
Stomach acid hurts the esophagus!
Take some Milk of magnesia.
 Why? It neutralizes the acid.

Modifications

You can change the Amylase experiment.
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Spit twice into the test tube instead of adding
amylase.
Use crushed cracker as your substrate and add
the Benedict’s indicator.
Incubate for 1 hour 45 min.
Boil for two min. This works great, just takes
a little longer!
Modifications

You can actually use pancreatin as your
enzyme source for all the experiments if
you want. Pancreatin contains all the
enzymes secreted by the pancreas.

You also can use boiled egg white instead
of albumin. You will not use biuret here,
but will look for the break down of the
egg. It will look like “snot” (sorry, best
analogy)
Modifications
You can use veg. oil instead of milk if you
like.
 You can also use phenolthalein or litmus
milk instead of phenol red as the indicator.
 You can have students do the experiment
with and without soap to see if the results
changes. (They will change)

Thank you!
Please check your test tubes.
 Any questions???
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