Biology 12: Digestion Review Answer Key
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Review Questions:
1. Define digestion. Why is this process important?
2. List the 4 functions of the digestive system.
3. How does saliva contribute to the formation of a bolus?
4. What prevents food form entering the nasal chamber and the trachea during
swallowing of food?
5. The opening to the larynx is called the
glottis
, which is covered when the
trachea moves up by the
epiglottis
.
6. What is responsible for heartburn and how is it normally prevented from occurring?
7. List the functions of the stomach. What is chyme?
8. What is the function of the gastric glands in the stomach?
9. What is an ulcer an why does it form?
10. List 4 functions of the small intestine. What molecule from the pancreas neutralizes
the acidity of chyme?
11. Describe the structure of villi and microvilli in the small intestine.
12. How are the small nutrient molecules absorbed across the wall of each villus? What
do they enter?
13. What is the function of the large intestine? How does its size compare with the small
intestine?
14. Which organ of the large intestine may play a role in immunity and if inflamed leads
to appendicitis?
15. Over 99% of the colon bacteria are E.coli (obligate anaerobes) , bacteria that die in
the presence of oxygen.
16. Describe the effects of bacteria in the large intestine. What does a high chloriform
count in swimming water mean?
17. Why will food poisoning and nerve stimulation cause diarrhea?
18. How does mil of magnesia and mineral oil work to overcome constipation?
19. What is the exocrine function of the pancreas? How does its products get to the
duodenum?
20. Name the 2 hormones secreted from the duodenal wall that signal the pancreas and
the gallbladder to release their products.
21. What are the components of bile? Give their function. What organ produces bile?
Where is it stored?
22. Explain why the liver is said to act as the gatekeeper to the blood.
23. Define deamination. What happens to those amino groups in the liver? How is urea
excreted?
24. List the 6 (7?) functions of the liver.
25. Name the enzyme found in the stomach. What is it formed from? What does it act
upon? What products will it form?
Questions:
1. Name the Pancreatic enzyme that in the duodenum will:
a. digest starch:
amylase
It forms the product maltose
b. digest Protein:
trypsin
It forms the product peptides
c. digest fat droplets: lipase
d. The end products of fat digestion reform
It forms the product fatty acids + glycerol
in the epithelial cells and are
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Biology 12: Digestion Review Answer Key
attached to
phospholipids
,
protein
a
¸ and
to form a temporary fat carrier molecule called
chylomicron
into the
cholesterol
. These carrier molecules are then dumped
lacteal
(part of the
lymphatic system
system) and will enter the blood-stream with the rest of the lymph at the left
subclavian
the
vein. They will be picked up eventually by
liver
which will convert them to a
The “bad” lipoproteins are called
lipoprotein
low density lipoproteins
And the “good” lipoproteins are called
(LDL
High Density lipoproteins
)
(HDL ).
When your body has too much energy, or saturated fat, the liver tends to put fats into the
LDL’s . When the body needs the energy from the fat, the liver tends to send it
to the cells in
HDL’s . LDL’s are associated with
atherosclerosis
(clogging of the arteries).
2. The 2 enzymes produced by the epithelial cells to complete the digestion of peptides
and maltose are
peptidases
and
maltase
The end products that are formed from these degradations are
and
glucose
amino acids
.
3. Lactose intolerance is due to
inability to digest milk - usually a lack of lactase
. The consequence of drinking milk for these individuals is
the sugar lactose is used by the bacteria in the gut as a food source - they
produce flatulus- causes cramping, irritation, diarrhea, etc
4. The stomach is directly connected to the esphagus
the
duodenum
above and
below.
5. The major food digested in the stomach is
Protein
hydrolyzed by the enzyme
.
Pepsin
, which is
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Biology 12: Digestion Review Answer Key
6. Among its chemical aspects, every digestive enzyme has a preferred pH and temp.
7. Before fats are digested by the enzyme
emulsified by bile
lipase
, they are first
.
8. Pancreatic juices enter the small intestine by way of the
duct and contain
enzymes
pancreatic duct
for the digestion of every type of
food.
9. The liver first receives the products of digestion by means of the
vein; any excess glucose is stored as
glycogen
(in the liver)
10. The secretion of digestive juices is controlled in general by
and
secretin
hepatic portal
gastrin, CCK
. (page 208 in text)
11. Surface area in the small intestine is increased greatly by the presence of
folds
and
villi
and
microvilli
.
12. Complete the following table:
Hormone
a. gastrin
Where
Cause of
Affects What
Affected Organ
Produced
Release
Organ?
Releases
Stomach
Meal high in
Stomach
HCl and
protein
b. secretin
c. CCK
pepsinogen
Cells of
Acid in
Pancreas and
Bile, Pancreatic
duodenal wall
duodenum
liver
juices
Cells of
Part. digested
Pancreas and
Bile, pancreatic
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Biology 12: Digestion Review Answer Key
duodenal wall
fat or protein
liver
juices
13. List 6 functions of the Liver
detoxifies blood
****
stores iron and fat soluble vitamins (I missed this one in the notes)
makes blood proteins
makes lipoproteins
maintains blood glucose levels
produces urea from breaking down amino acids
converts Hb from RBCs into billirubin and biliverdin
produces bile
14. Vitamins are often portions of
coenzymes
,
necessary for cellular metabolism.
a. In which part of the digestive tract are nutrient molecules absorbed?
S.intestines
b. The absorbed nutrient molecules enter what vein associated with the intestine?
Hepatic portal vein
c. In which part of the digestive tract does pancreatic juice enter?
d. In which part of the digestive tract does bile enter?
duodenum
duodenum
e. What parts of the digestive tract do not actually contain food and might be called
accessory organs of digestion?
Salivary glands, pancreas, liver, gallbladder
f. What parts of the digestive tract do not have ducts entering them and do not secrete
digestive juices?
Esophagus, large intestine, rectum, anus
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Biology 12: Digestion Review Answer Key
Digestion of Carbohydrate (starch)
Starch digestion begins in the
empty from the
enzyme
salivary
amylase
disaccharide
mouth
. Here the ducts
glands. The salivary juice contains the
and this enzyme breaks down starch to the
maltose
duodenum
. Starch is also acted on in the
. Here, a duct empties from the
Pancreatic juice contains the enzyme
amylase
down starch to the disaccharide
maltose
pancreas
which breaks
. Starch digestion is
complete when this disaccharide is broken down to
glucose
,a
monosaccharide, which can be absorbed by intestinal villi. The enzyme that converts
maltose to glucose is called maltase
epithelial
and this enzyme is secreted by
cells of the intestinal villus.
17. Digestion of Protein (meat)
Protein digestion begins in the
stomach
. The gastric
Glands line the wall of the stomach. They secrete the enzyme
pepsinogen (pepsin)
which breaks down protein to
peptides
. Another enzyme
called
is secreted by the
pancreas
this enzyme acts on protein in the
duodenum
, also breaking down protein
to
. Protein digestion is complete when peptides are
trypsin
peptides
broken down to
amino acids
and
, molecules small enough to be
absorbed by the villi. This is achieved by the enzyme
produced in the epithelial cells of the intestinal villus.
peptidase
that is
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Biology 12: Digestion Review Answer Key
18. Digestion of fat (butter)
Fat is first emulsified by
bile
, a substance made by the
liver and stored in the
gall bladder
. The contents of the latter
enter the small intestine by way of the
bile
has been emulsified, it is broken down by the enzyme
duct. After the fat
lipase
which
is found in pancreatic juice, which enters the small intestine by way of the pancreatic
duct. Fats are broken into
glycerol
and fatty acids, molecules
small enough to be absorbed by intestinal villi. After resynthesis, fats enter the
lacteal
, which are part of the lymphatic system.
19. Path of food.
a. Food consists of the large organic molecules
carbohydrates
and
nucleic acids
digested is
and
lipids
and
. In the mouth, the only type of food
starch
. The mouth has a
The food passes down the long tube called the
contraction called
proteins
peristalsis
neutral
pH.
esophagus
. A rhythmic
pushes the food along. After passing
through a sphincter, (circular muscle), the food enters the stomach
where the primary food acted on is
protein
chyme, passes through another sphincter into the
Two ducts enter this organ: they are the
pancreas
. The food, now called
duodenum
pancreatic
and the
bile
.
duct from the
duct from the
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Biology 12: Digestion Review Answer Key
gall bladder
. Bile contains an
emulsifier
which
divides fat up into fat droplets. Pancreatic juice contains enzymes that act on
lipids
,
Lining the walls of the intestine are
protein
, and
epithelial cells
with
carbohydrates
microvilli
on the apical surface of each cell. The epithelial cells produce enzymes that finish
digestion by converting
maltose
to glucose and
peptides
to amino acids. Thus the small nutrient molecules that are absorbed by the villi are
Amino acids
,
Fatty acids and glycerol
glucose
,
. Fat products enter the
and the other molecules enter the
hepatic
This vein takes the nutrients to the
liver
nucleotide
,and
lacteal
portal vein.
,an organ of
homeostasis. For example, this organ stores glucose as
glycogen
and
always keeps the blood glucose level constant. This organ can also remove amino
groups from
amino acids
urea
and convert the amino groups to
a nitrogenous waste product.
20. Digestive Enzyme Activity. For each combination of substances below, decide
whether digestion will or will not occur at the maximum rate. Give an explanation if
digestion will NOT occur maximally.
a. trypsin, NaHCO3, egg white, warm gently
maximal rate
Biology 12: Digestion Review Answer Key
b. salivary amylase, water, egg white, warm gently
no reaction - wrong substrate! (amylase works on starch!)
c. Pepsin, HCl, egg white, freeze
no reaction - enzyme will not work when temperatures drop that low!
d. pancreatic amylase, HCl, starch, heat to boiling
no reaction - boiling denatures the enzyme (+ the pH is wrong!)
e. lipase, NaHCO3, fats, warm gently
maximum rate
f. maltase, HCl, maltose, warm gently
will work, but not very well. Wrong pH
g. peptidases, fat, HCl, warm gently
no reaction - wrong substrate, + wrong pH
h. pepsin, HCl, egg white, warm gently
maximum rate
i. trypsin, starch, water, warm gently
no reaction - wrong substrate
j. HCl, egg white, water, warm gently
no reaction - no enzyme!
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