7/29/2019 Results and Discussion - Digestive Physiology
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3. Results
3.1. Physical Digestion of Macromolecules
Condition Salivation
Upon seeing food With salivation
Upon smelling food Increased salivation
Upon eating Increased salivation
Table 1. Occurrence of salivation upon certain
conditions
3.2. Chemical Digestion of Carbohydrates
3.2.1. Lugols Test
Set-up Number Lugols
Test
C1 (water) +
C2 (amylase) -C3 (amylase + HCl) +
C4 (amylase + heat) +
Table 2. Test reactions to starch indicators
3.2.2. Benedicts Test
Set-Up Number Benedicts Test
C1 (water) ++
C2 (amylase) + and +++
C3 (amylase + HCl) +
C4 (amylase + heat) + and ++
Table 3. Test reactions to maltose indicator
3.3. Chemical Digestion of Proteins
Set-up Number Observation
P1 (pepsin and water) +
P2 (pepsin and HCl) +++
P3 (pepsin and HCl on ice) +
P4 (water and HCl) -
P5 (pepsin and NaOH) -
Table 4. Observations to protein digestion
3.4. Chemical Digestion of Fats
Set-up Number Average pHF1 (water) 6.5
F2 (pancreatin) 6.25
F3 (pancreatin + bile salts) 5.875
Table 5. Test solutions average pH within 1 hour
at 20-minute intervals
4. Discussion
Mastication is the chewing or grinding of food into
bolus which involves the teeth, tongue and most
importantly, the three salivary glands. Saliva is
essential in physical digestion as it kills the bacteria
in the food thus keeping the mouth clean andbreaking down food
into simple carbohydrates for
easier digestion further onwards.
Though salivation can be considered an involuntary
process, increased activity can be instigated by the
autonomic nervous system. It is often stimulated by
the entry of food or irritants into the mouth and
thoughts of or smell of food. This explains the
increased activity of the salivary glands when the
subject smelled and consumed her food.
An enzyme in saliva called amylase is the primary
component in cleaving starch. The presence of starch
can be determined by subjecting a sample to Lugols
Iodine Test. This solution is comprised of potassium
iodide and elemental iodine in distilled water. If
starch has been digested, the sample turns dark blue
and black.
In the results obtained, only the set-up with amylase
turned amber signifying the absence of starch
because it was the set-up that simulated the most
ideal environment for cleaving starch. The set-up
with only water is evidently incapable of any form of
digestion thus the starch remained intact. The last two
set-ups, however, were tests for the potential
denaturation of amylase because this occurrence havetemperature
and pH as triggering factors.
Amylases optimum pH or the pH at which it is most
functional is around 7 meaning it thrives in
practically neutral conditions. Now, having been
subjectedas demonstrated in C3to an acidic
environment causes it to denature thus changing its
shape. Applying the lock-and-key theory, the
substrate molecule cannot fit into the newly
denatured active site because their shapes are not
complementary anymore. Starch cannot be
accommodated by the new structure of amylase,
leaving it undigested. The same can be essentiallysaid for
temperature. High temperaturesusually
ranging above 100Ccause amylase to denature
because of the increase in the molecules kinetic
energy. The molecules become more excited in
colliding into each other damaging and remodelling
the enzymes previous structure. This explains the
37C water bath that the set-ups must be immersed in
after because it is the optimum temperature for
digestion.
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The carbohydrates that were broken down by
amylase are turned into maltose, a disaccharide.
Benedicts solution tests for the presence ofmaltose
in the previous set-ups. The presence of maltose can
be interpreted from the colour that the set-ups will
change into, with green indicating the least amount of
maltose, yellow indicating moderate amounts, and
orange or red indicating large amounts.
For this test, the set-up with water showed moderate
amounts of maltose signifying that breakdown of
carbohydrates took place. Since the change into
maltose is caused by hydrolysis and the set-up was
incubated at optimum temperature for 30 minutes, it
is possible that starch was cleaved through hydrolysis
even without the aid of amylase. C2 naturally
produced the highest amount of maltose because of
its ideal conditions. However, the incubation period
was not sufficient to enable the digestion of all
carbohydrates present, hence the green layer.C3, on the other
hand, reflected the least amount of
maltose because starch was not processed in the first
place due to unfavourable pH levels. As for C4, the
exposure to boiling temperature was not long enough
as to denature all of the amylase so there were still
functioning proteins left when finally subjected to the
optimum temperature.
Protein digestion into peptides begins in the stomach
but its bulk is performed in the small intestine.
Parietal cells in the gastric glands of the stomach
produce HCl which activates pepsinogen. Pepsinogen
is the precursor of pepsin, an enzyme responsible forprotein
digestion. This enzyme has an optimum pH of
2therefore the production of HCland an
optimum temperature of about 37C. All the set-ups
were immersed in a 37C water bath after preparation.
In set-up P1, though water is technically neutral in
pH, it is considerably more basic than the conditions
pepsin is most attuned to. That is why only minimal
digestion occurred. P2, conversely, demonstrates the
optimum environment for protein digestion therefore
yielding the highest amount of digested proteins. In
P3, pepsin was not exposed to its optimum
temperature but low temperatures have been found tobe not
particularly damaging to the structure of the
enzyme. It only slows its activity so pepsin was still
able to perform digestion albeit minimal. Set-up P4
did not contain pepsin so obviously digestion cannot
occur. NaOH in P5 is an extremely strong base,
proving detrimental to the functional structure of
pepsin. Since pepsin only thrives in extremely acidic
surroundings, an extreme base would inevitably
cause its denaturation. This will render it incapable of
starting digestion because of active site-substrate
molecule incompatibilities.
Fat digestion is perhaps the most difficult digestion to
enact because of fats insolubility in water. Bile is
produced by the liver and stored and concentrated in
the gallbladder, from which it will be secreted as a
response to the hormone cholecystokinin. This will
act as an emulsifying agent. Lecithin in bile (which is
amphipathic) forms micelles around microscopic
droplets of fat through the hydrophobic tail fat
interaction and hydrophilic headwater interaction.
This maximizes the lipid-water interaction and
prevents the fat molecules from aggregating. Lipase
found in pancreatin will then commence the
digestion. The optimum pH for lipid digestion is
around 6.5 to 9. Bile salts and water are products of
neutralization reactions that occur in the liver.
Since pancreatin was not added to F1, the set-up will
have no source of lipase thus a reaction cannot occur.It will
maintain a pH of 6.5, the lowest in the range of
optimum pH level for lipid digestion. Theoretically,
F2 should have become more basic with the presence
of pancreatin, which normally thrives in basic
environments. The same could be said for F3, which
should have been the most basic due to the addition
of bile salts which are essential neutralizers.
REFERENCES
[1] Hallare. Student Handbook in General Zoology
Part 2. 2012
[2] Tolliver, K. (n.d.). What is Bile Salt? In eHow.
Retrieved February 17, 2013 from http://www.ehow.
com/about_5525802_bile-salt.html
[3] What is Mastication. (n.d.). In wiseGEEK.
Retrieved February 17, 2013 from www.wisegeek.
com/what-is-mastication.htm
[4] Bailey, R. (n.d.). Salivary Glands and Saliva.
Retrieved February 17, 2013 from
[5] Amylase Enzyme: The Effects of Temperature.
(n.d.). InAllSands
. Retrieved February 17, 2013
fromhttp://www.allsands.com/science/science/amylaseenz
ymeh_wpp_gn.htm
[6] Bloom, C. (2011, October 11). Effect of
temperature and pH on enzyme activity. In
slideshare. Retrieved February 17, 2013 from
http://www.slideshare.net/clairebloom/effect-of-
temperature-and-ph-on-enzyme-activity
