Biology & Life Sciences Chapter 41 Homework Digestive Enzymes Break Food Down Into Its

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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-