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Notes to Instructors
Chapter 41 Animal Nutrition
What is the focus of this activity?
Many of the organ systems in mammals are designed to handle the bulk flow of
substances into and out of the body. The digestive system is designed to handle the bulk
processing and digestion of food. The food we eat is composed of macromolecules—for
What is this particular activity designed to do?
Activity 41.1 How are form and function related in the digestive system?
This activity is designed to help students understand:
What misconceptions or difficulties can these activities reveal?
Activity 41.1
Question 2: If you haven’t encountered it already, you will discover that many students
do not understand “how bacteria eat.” They understand that bacteria are decomposers and
Question 3: The figure reduces the digestive tract to the basics to allow students to see
the direct connections between its various parts. For many students this understanding
268 Activity 41.1
Question 5: Many students don’t understand that the food that enters the digestive tract is
technically not inside the body. It is contained in a space that exists within the body. To be
Question 7: Most students understand that enzymes operate using a lock-and-key-type
Question 9: Students may not understand the roles that the hepatic portal vein and the
liver play in maintaining homeostasis of the blood (and therefore the body in general). In
that case, it will be difficult for them understand how insulin and glucagon can act to
control blood sugar levels (see Chapter 45).
Answers
Activity 41.1 How are form and function related
in the digestive system?
1. What is the overall function of digestion (as a whole)?
Digestion breaks down complex carbohydrates, nucleic acids, proteins, and lipids
2. a. How do bacteria eat?
When they encounter a food source,
b. How do amoebas eat?
Amoebas trap small food items in
Activity 41.1 269
How are their eating styles similar to what we see in humans? How are they
different?
c. Similarities
with bacteria
In both humans
and bacteria,
d. Differences
from bacteria
In humans a part
of the outside
and be lost.
e. Similarities with
amoeba
As with bacteria,
humans and
f. Differences
from amoeba
In amoebas, the
food vacuoles
3. Label the parts of the mammalian digestive tract in the diagram, and state the major
function(s) of each part.
mouth and
teeth
esophagus stomach
small intestive
large intestine
270 Activity 41.1
How does the structure of each part reflect its function?
a. Mouth/teeth b. Esophagus c. Stomach
d. Small
intestine
e. Large
intestine
The mouth and
teeth function to
only on sur-
faces. Salivary
amylase begins
the digestion of
starch to smaller
polysaccharides.
The esophagus
is muscular and
standing on your
head.)
The stomach is
muscular and has
in the wall of the
stomach), break
down large food
particles into
smaller ones and
increase the SA/V
ratio of the food
particles. Pepsin
(a protein-
digesting
The majority of
enzymatic
the animal's
body length. The
walls of the
small intestine
are highly
folded. The
folds increase
surface area.
The surface of
the folds
The primary
function of the
salts and calcium
into the feces. In
addition, it houses
a population of
bacteria that
produce some
important
vitamins (e.g.,
vitamin K)
required by
Activity 41.1 271
Using the understanding of the structure and function of the digestive system you
gained from the model in question 4, answer the questions.
5. The mammalian digestive tract has been called an extension of the outside world
that you enclose in your body.
a. What does this statement mean? Consider what would happen if you swallowed a
marble. Is the marble ever “inside your body”?
If you swallowed a marble, it could pass through your entire digestive tract and
b. At what point in the digestive process is food officially inside the body?
Food is not officially “inside the body” until it has crossed a cell membrane.
c. How is mammalian digestion more efficient than the type of digestion seen in
bacteria?
In bacteria, some of the secreted enzymes may diffuse away from the food
4. Make a larger copy of the diagram in question 3. Use this larger diagram to
model or trace what happens to a food particle from the time it enters the mouth
until its indigestible remains are egested, or eliminated. Include all of the following
terms in your discussion. Also, note on the diagram the function of each and where it
is found in the digestive system.
carbohydrate
fat
nucleic acid
protein
cardiac orifice
epiglottis
pyloric sphincter
pharynx
pepsinogen
lipase
pepsin
salivary amylase
bile
dipeptidase
saliva
amylase
pancreas
nuclease
gastric acid (HCl)
bolus
microvilli
lacteals
capillaries
feces
intestinal bacteria
hepatic portal vein
fiber or roughage
6. Digestion (in humans and many other animals) is both physical and chemical.
Among the chief chemical agents of digestion are the digestive enzymes. What do
enzymes do to food?
Digestive enzymes break food down into its component macromolecules—for
7. Have you ever heard the old adage: “Be sure to chew your food 20 times before
swallowing?”
a. What, if any, effect would this chewing have on how well the digestive system
functions? Keep in mind that enzymes work only on the surfaces of food
particles. Explain.
Chewing your food breaks it down into smaller pieces. This increases the
surface-area-to-volume ratio of the total mass. Keep in mind that food moves
b. How does the function of the teeth complement the function of one of the
digestive chemicals in the stomach? Be sure to name the specific chemical in
your answer.
Both the teeth and the hydrochloric acid in the stomach break down larger pieces
8. Although enormous quantities of various enzymes are added to the contents of the
duodenum of the small intestine, no traces of enzymatic activity are left in the
intestinal contents when they pass into the large intestine (colon). Why? What
happens to the enzymes?
Enzymes are made of protein. When no food remains for digestion, the enzymes will
9. Most of the blood that leaves the digestive tract of a human is collected into a series
of veins that merge to form the hepatic portal vein. The hepatic portal vein carries
blood to the liver, where the hepatic portal vein divides again into a system of
venules and then liver capillaries. The liver capillaries drain into the hepatic vein,
272 Activity 41.1
which carries blood to the vena cava. The vena cava carries blood from the body to
the right atrium of the heart. Some of the products of digestion enter a different
system of transport, the lacteal system. The lacteal system bypasses the liver and
carries its contents directly to the right atrium of the heart.
a. Which products of digestion are carried in the blood to the liver?
b. Which products of digestion are carried via the lacteal system?
c. During the first hour after a heavy meal, how does the concentration of glucose
in the blood going from the small intestine to the liver compare to the
concentration entering the right atrium of the heart?
If we assume the meal contained carbohydrates, then the blood going from
d. Similarly, how does the concentration of amino acids compare?
The liver also regulates the concentration of amino acids in the circulating blood.
e. How does the concentration of fat leaving the small intestine compare to the
concentration in the right atrium?
The products of lipid digestion (as well as some small fats) enter the lacteal
10. How does an herbivore such as a cow extract the glucose from the cellulose in its
diet? What characteristics of the structure and function of the digestive tract of a
ruminant suit it for this function?
Symbiotic prokaryotes and protists are housed in the cow’s rumen. The cow chews
Activity 41.1 273
274 Activity 41.1
41.1 Test Your Understanding
1. A peanut butter and jelly sandwich contains a variety of carbohydrates, fats, and
proteins. Complete the graph below to indicate the relative percentages of
carbohydrate, fat, and protein that remain in this ingested food as it progresses from
your mouth through your digestive tract. Explain your reasoning.
Key: Protein = xxxxx; Carbohydrate = ---------; Fat = oooooooo
100%
Activity 41.1 275
A small amount of the carbohydrates has been digested by the salivary amylase in
the mouth. The amount digested depends on the length of time the food remained
2. A good rough generalization is that the more meat in the diet of a species of animal,
the shorter its intestine. In comparison, herbivores have long intestines (length
always being relative to total body length). How can this be explained?
In general, vegetation or plant materials are more difficult to digest than meat
(animal muscle protein). Although the majority of digestive enzymes are added to
3. What would happen to the normal function of the digestive tract if part of one of the
following organs was removed or greatly reduced in size (for example, as the result
of surgery following an accident)? How would a person’s eating habits need to
change to accommodate the reduction in size?
a. Stomach
If part of the stomach were removed, you would not be able to eat very much at
any given time. The volume consumed per unit time would have to be reduced.
276 Activity 41.1
4. A friend of yours has come up with a new idea for people who don’t have time to
eat. He has developed a high-powered Blenderizer that breaks food up into very
small particles. He has tested his product on amoeba and Paramecia. Both of these
single-celled organisms can pick up these small particles and incorporate them
into food vacuoles. Your friend is hoping to market the Blenderizer to busy people
who could blenderize their food and use an IV bag and tube to run the food directly
into their blood system. Because people could hide the system under their clothes,
they could essentially eat any time without it interfering with meetings and other
activities. Your friend comes to you for advice and possible financial support to get
his idea off the ground. What would you say to him?
Anyone who used this system would probably die. The proteins and other species-
