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Name ______________________________ Class ___________________ Date __________________
Digestive and Excretory Systems
Study Guide
Answer Key
SECTION 1. NUTRIENTS AND
HOMEOSTASIS
SECTION 2. DIGESTIVE SYSTEM
1. to break down large complex molecules in
food into smaller molecules that can be
used by the body
2. mechanical digestion: chewing food,
smooth muscles churning and mixing
food; chemical digestion: enzymes
breaking down food, stomach acid
digesting protein, or other chemicals such
as bile breaking down fats
3. smooth muscles contract and relax to keep
food moving, and sphincters prevent food
from backing up.
4. nutrients are absorbed and distributed to
the cells; undigested materials are
eliminated as liquid and solid wastes
5. salivary amylase, amylase: break down
starches into simpler sugars; pepsin,
peptides: break down proteins; lipase:
breaks down fats
Process Diagram: Mouth—salivary
amylase break down starches into simple
sugars; Stomach—HCl and pepsin break
down proteins; chyme forms; Small
Intestine—pancreas helps finish digestion
of sugars and break down fats; liver and
gallbladder release bile to digest fats
6. Pepsin is active only when there is food in
the stomach; a layer of mucus keeps
stomach acids from digesting the lining
7. esophagus “carries food” from the mouth
to the stomach
8. Examples: two hands squeezing dough out
of a plastic tubing; squeezing toothpaste
out of a tube
1. water—fluid balance, chemical reactions
2. carbohydrates, simple and
complex—energy
3. proteins—growth, repair, enzymes,
hormones
4. fats, saturated and unsaturated—energy,
used in many structures
5. minerals—homeostasis, building, repair
tissues
6. vitamins, water– and fat-soluble—
regulate cell functions, growth,
development
7. you lose about this much each day
through sweat, urine, and respiration
8. vegans must combine plant foods such as
beans and rice to obtain all eight essential
amino acids
9. saturated fats are solid at room
temperature; unsaturated fats are liquid at
room temperature
10. carbohydrates and fats
11. to provide adequate amounts of all six
nutrients for the rapid growth that occurs
during these years
12. these foods, unlike high-sugar or
processed foods, are rich in fiber,
vitamins, and minerals
13. the number of Calories and Calories from
fat must be multiplied by the number of
servings per product to get an accurate
Calorie count
14. It helps you to compare the number of
Calories, and type and amount of nutrients
among products, then choose the best one.
15. calorie is the amount of energy required
to raise one gram of water one degree
Celsius; Calorie is a measure of energy
from food and equals 1000 calories
16. vitamins are necessary to support the
many life functions of cells, the smallest
unit of life
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
i
Digestive and Excretory Systems
Name ______________________________ Class ___________________ Date __________________
Study Guide B continued
SECTION 3. ABSORPTION OF
NUTRIENTS
1. Absorption is the process by which nutrients
move out of the digestive system and into
the circulatory and lymphatic system.
Without absorption, nutrients cannot reach
the cells.
2. lining of the small intestine, villi, microvilli
3. the lining is ridged and folded, thousands of
villi cover the lining, and thousands of
microvilli cover each villi, greatly increasing
surface area
4. to allow more time for nutrients to be
absorbed
5. Materials absorbed— simple sugars, amino
acids, minerals; Distribution— circulatory
and lymphatic systems
Part of intestine: jejunum; Materials
absorbed: glucose, amino acids, vitamin C,
B vitamins, some water
Part of intestine: ileum; Distribution:
circulatory and lymphatic systems
6. Enzymes use some of the nutrients to build
more complex molecules that cells need; the
liver stores some nutrients for future use.
7. by absorbing some water and salts
8. undigested plant fiber, bile pigments, dead
bacteria, traces of undigested fat and protein
9. helpful—some bacteria synthesize vitamins
K and B12; harmful—if some harmless
bacteria overgrow other bacteria, they can
reduce water absorption and cause severe
diarrhea
10. the rectum stores the feces; feces pass out of
the body through the anus.
11. they can help students remember that the
microvilli are very tiny, hairlike projections
on the villi.
12. Sample answers: Students might sketch a
paper towel absorbing a spill or think of
clothes absorbing liquids spilled on them,
paper absorbing ink, or chemicals absorbing
oil spilled on a beach
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
ii
Digestive and Excretory Systems
Name ______________________________ Class ___________________ Date __________________
Section 1: Nutrients and Homeostasis
Study Guide
KEY CONCEPT
Cells require many different nutrients.
VOCABULARY
mineral
Calorie
vitamin
MAIN IDEA: Six types of nutrients help to maintain homeostasis.
Fill in the concept map to summarize what you know about the six nutrients.
Six nutrients needed every day
6. vitamins,
water- and
fat-soluble
4.
2.
needed for
needed for
3.
1. water
energy
needed for
needed for
5.
regulate cell
needed for functions, growth,
development
needed for
growth,
repair, enzymes,
hormones
7. Many dietary experts recommend drinking about 8 glasses of water a day.
Why do you need this much fluid to maintain homeostasis?
_______________________________________________________________
8. Explain why vegans, who eat no animal products, might have difficulty
obtaining all 8 essential amino acids from their diet.
_______________________________________________________________
_______________________________________________________________
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
1
Digestive and Excretory Systems
Section 1: Nutrients and Homeostasis
Name ______________________________ Class ___________________ Date __________________
Study Guide continued
9. What is the difference between saturated and unsaturated fats?
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10. Which of the six nutrients supply the body with energy?
_______________________________________________________________
MAIN IDEA: Meeting nutritional needs supports good health.
11. Why is eating a balanced diet particularly important during pre-teen and
teen years?
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_______________________________________________________________
12. Why do most dietary experts recommend that you obtain most of your
Calories from whole grains, vegetables, and fruits?
_______________________________________________________________
13. You are checking the number of Calories, and Calories from fat, on a food
label. What other information do you need to know to get accurate Calorie
counts?
_______________________________________________________________
_______________________________________________________________
14. How can the information on a food label help you make good eating choices?
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Vocabulary Check
15. The words calorie and Calorie both refer to a unit of energy. What is the
difference in meaning between these two words?
_______________________________________________________________
_______________________________________________________________
16. The Latin term vita means “life.” How does this meaning relate to the function
of vitamins?
_______________________________________________________________
_______________________________________________________________
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
2
Digestive and Excretory Systems
Section 1: Nutrients and Homeostasis
Name ______________________________ Class ___________________ Date __________________
Section 2: Digestive System
Study Guide
KEY CONCEPT
The digestive system breaks down food into simpler molecules.
VOCABULARY
digestion
esophagus
chyme
digestive system
peristalsis
small intestine
sphincter
stomach
bile
MAIN IDEA: Several digestive organs work together to break down food.
1. What is the main function of digestion?
_______________________________________________________________
_______________________________________________________________
2. Give an example of mechanical and chemical digestion.
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_______________________________________________________________
3. How do smooth muscles and sphincters keep food moving in one direction
throughout the digestive system?
_______________________________________________________________
_______________________________________________________________
4. What happens after digestion is completed?
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MAIN IDEA: Digestion begins in the mouth and continues in the stomach.
5. Fill in the chart below to help you remember facts about key digestive
enzymes.
Enzyme
Function
salivary amylase,
amylase
pepsin, peptides
lipase
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
3
Digestive and Excretory Systems
Section 2: Digestive System
Name ______________________________ Class ___________________ Date __________________
Study Guide continued
MAIN IDEA: Digestion is completed in part of the small intestine.
Fill in the process diagram below to summarize the digestion of food as it moves
through the mouth, stomach, and small intestine. Use Figure 2.4 to help you.
Mouth
• Food is chewed and
shredded.
Stomach
• Smooth muscles
churn and mix food.
Small Intestine
• Smooth muscles
churn and mix food.
• Protein digestion
finished.
• Food is swallowed.
6. What keeps the stomach from digesting itself?
_______________________________________________________________
_______________________________________________________________
Vocabulary Check
7. The word esophagus is based on the Greek terms ois-, which refers to
“carrying something,” and phagos, which means “food.” How can these Greek
terms help you remember the meaning of esophagus?
_______________________________________________________________
8. Think of an analogy that might help you to explain the meaning of peristalsis
to someone who does not know the word.
_______________________________________________________________
_______________________________________________________________
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
4
Digestive and Excretory Systems
Section 2: Digestive System
Name ______________________________ Class ___________________ Date __________________
Section 3: Absorption of Nutrients
Study Guide
KEY CONCEPT
Nutrients are absorbed and solid wastes eliminated after digestion.
VOCABULARY
absorption
microvilli
villi
MAIN IDEA: Most absorption of nutrients occurs in the small intestine.
1. What is absorption, and why is it important to your body?
_______________________________________________________________
_______________________________________________________________
2. Name the three structures in the small intestine that absorb most of the
nutrients from chyme.
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3. How do these three structures increase the surface area of the small intestine?
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4. Why is it important that food move slowly through the small intestine?
_______________________________________________________________
5. Fill in the chart summarizing absorption in the three parts of the small
intestine.
Part of Small
Intestine
Materials Absorbed
Distribution
duodenum
circulatory system
fat-soluble vitamins, vitamin B12, fatty
acid, cholesterol, some water
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
5
Digestive and Excretory Systems
Section 4: Excretory System
Name ______________________________ Class ___________________ Date __________________
Study Guide continued
6. What happens when nutrient-rich blood leaves the small intestine and enters
the liver?
_______________________________________________________________
_______________________________________________________________
MAIN IDEA: Water is absorbed and solid wastes are eliminated from the
large intestine.
7. How does the large intestine help to maintain the body’s fluid balance, or
homeostasis?
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8. What materials make up the feces?
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9. In what ways can bacteria in the large intestine be helpful or harmful?
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10. How is solid waste eliminated from the body?
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Vocabulary Check
11. The Latin word villus means “shaggy hair,” and micro refers to something that
is unusually small. How can these two terms help you remember the meaning
of microvilli?
_______________________________________________________________
_______________________________________________________________
12. Draw a sketch or think of an analogy to illustrate the meaning of absorption.
Think of times you have watched water or other liquids being absorbed by
something.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
6
Digestive and Excretory Systems
Section 4: Excretory System