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BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
CHAPTER 21
Nutrition and Digestion
From PowerPoint® Lectures for Biology: Concepts & Connections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Getting Their Fill of Krill
• Animals obtain and
process nutrients in a
variety of ways
• Humpback whales eat
small fishes and
crustaceans called krill
– This painting shows how
the whales corral their
food using “bubble nets”
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Humpback whales strain their food from
seawater using large, brushlike plates called
baleen
– When they feed, they take in large amounts of
seawater in which the fish and krill live
– They must filter out the water in order to get a
meal
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• In a typical day, a humpback whale’s digestive
system will process as much as 2 tons of fish
and krill
– They store the excess energy they harvest in the
form of blubber
– In about 4 months, a humpback whale eats,
digests, and stores as fat enough food for an
entire year
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OBTAINING AND PROCESSING FOOD
21.1 Animals ingest their food in a variety of ways
• Animal diets are highly
varied
– Herbivores are plant-eaters
– Carnivores are meat-eaters
– Omnivores eat both plants
and other animals
Figure 21.1A
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• Most animals ingest chunks of food
Figure 21.1E
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– Some animals are
suspension feeders,
consuming particles
from water
– Some are substrate
feeders, living in or
on their food source
Figure 21.1B, C
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– Some are fluid
feeders, sucking
liquids
Figure 21.1D
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• Flagellated choanocytes filter food from the
water passing through the porous body
Choanocyte in
contact with
an amoebocyte
Pores
WATER
FLOW
Skeletal
fiber
Central
cavity
Choanocyte
Flagella
Amoebocyte
Figure 18.3C
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Coiled
thread
Tentacle
Capsule
(nematocyst)
“Trigger”
Discharge
of thread
Prey
CNIDOCYTE
Figure 18.4D
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18.6 Flatworms are the simplest bilateral animals
• Phylum Platyhelminthes
– Planarians have a simple nervous system
consisting of a brain, sense organs, and
branching nerves
– As in cnidarians,
the mouth of a
flatworm is the
only opening for
its gastrovascular
cavity
Digestive tract
(gastrovascular
cavity)
Mouth
Eyespots
Nervous
tissue clusters
Figure 18.6A
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Nerve cords
Bilateral symmetry
VISCERAL MASS
Coelom
Kidney
Heart
Reproductive
organs
Digestive
tract
MANTLE
Shell
Mantle
cavity
RADULA
Radula
Anus
Gill
Mouth
FOOT
Nerve
cords
Mouth
Figure 18.9A
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• Most leeches are free-living carnivores, but
some suck blood
Figure 18.11C
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– The water vascular system has suction-cup-like
tube feet used for respiration and locomotion
Anus
Spines
Stomach
TUBE FEET
CANALS
Figure 18.14A
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21.2 Overview: Food processing occurs in four
stages
Small
molecules
Pieces
of food
Mechanical
breakdown
Nutrient
molecules
enter body
Chemical breakdown
(enzymatic hydrolysis) cells
Undigested
material
Food
1 INGESTION
2 DIGESTION
3 ABSORPTION
4
ELIMINATION
Figure 21.2
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21.3 Digestion occurs in specialized compartments
• Food is digested in compartments housing
hydrolytic enzymes
• Most animals have a specialized digestive tract
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• Relatively simple animals have a sac with a
single opening
– This is called a gastrovascular cavity
– Example: hydra
Mouth
Tentacle
Flagella
Hydrolytic
enzymes
Food
particle
Food
(Daphnia,
a water
flea)
Engulfment
Gastro- of food
vascular particle
cavity
Digestion in
food vacuole
Figure 21.3A
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• In most animals, the digestive compartment is
an alimentary canal
– This is a tube running from mouth to anus
– This tube is divided into specialized regions that
process food sequentially
Crop
Esophagus
Pharynx
Gizzard
Intestine
Anus
Mouth
EARTHWORM
Wall of intestine
Interior of intestine
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Figure 21.3B
Esophagus
Stomach
Gizzard
Anus
Esophagus
Stomach
Gizzard
Intestine
Crop
Gastric pouches
Mouth
GRASSHOPPER
Intestine
Mouth
Crop
Anus
BIRD
Figure 21.3B (cont)
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HUMAN DIGESTIVE SYSTEM
21.4 The human digestive system consists of an
alimentary canal and accessory glands
• When food is swallowed, it is moved through
the alimentary canal by peristalsis
– Peristalsis is rhythmic muscle contraction in the
walls of the digestive tract
– Ringlike sphincter muscles regulate the passage
of food
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Oral cavity
Mouth
Tongue
Salivary
glands
Pharynx
Esophagus
Liver
Stomach
Pyloric
sphincter
Gallbladder
Pancreas
Small
intestine
Stomach
Small
intestine
Large
intestine
Rectum
Anus
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Figure 21.4
21.5 Digestion begins in the oral cavity
• The teeth break up food
• Saliva moistens it
• Salivary enzymes begin the hydrolysis of starch
• The tongue pushes the chewed food into the
pharynx
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TEETH
Incisors
Canine
Premolars
Molars
Tongue
“Wisdom”
tooth
Salivary
glands
Opening of a
salivary gland duct
Figure 21.5
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21.6 The food and breathing passages both open
into the pharynx
• The swallowing reflex moves food from the
pharynx into the esophagus
– At the same time, food is kept out of the trachea
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Bolus of food
Epiglottis
up
Tongue
Pharynx
Epiglottis
down
Larynx
Trachea
(windpipe)
Esophageal
sphincter
Larynx
down
Larynx
up
Esophagus
Esophagus
Sphincter contracted
Sphincter relaxed
Sphincter contracted
Figure 21.6
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21.7 The esophagus squeezes food along to the
stomach
• Peristalsis in the esophagus moves food boluses
into the stomach
Circular
muscle layer
Bolus of
food
Longitudinal
muscles
contract,
shortening
passageway
ahead of bolus
Longitudinal
muscle layer
Relaxed
muscles
Circular
muscles
contract,
constricting
passageway
and pushing
bolus down
Relaxed
muscles
Stomach
Figure 21.7
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21.8 The stomach stores food and breaks it down
with acid and enzymes
• The stomach mixes food with gastric juice
– The gastric juice contains pepsin, which begins
the hydrolysis of protein
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Interior surface
of stomach
Food particle
Pits
Gastric juice
(mucus, HCI,
and pepsinogen)
3
Epithelium
Gastric
juice
Pepsinogen
2
Mucous
HCI
cells
Pepsin (active
enzyme)
Pyloric
sphincter
STOMACH
Gastric
gland
1
Chief cells
Pariental cells
Figure 21.8
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21.9 Connection: Bacterial infections can cause
ulcers
• New evidence suggests that a spiral-shaped
prokaryote causes gastric ulcers
– Helicobacter pylori growth erodes protective
mucus and damages the stomach lining
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21.10 The small intestine is the major organ of
chemical digestion and nutrient absorption
• Alkaline pancreatic juice neutralizes stomach
acids
– Its enzymes digest polysaccharides, proteins,
nucleic acids, and fats
• Bile emulsifies fat droplets for attack by
pancreatic enzymes
– It is made in the liver and stored in the gall
bladder
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Bile
Liver
Stomach
Gallbladder
Bile
Duodenum of
small intestine
Acid chyme
Pancreas
Figure 21.10A
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• Enzymes from the walls of the small intestine
complete the digestion of many nutrients
Table 21.10
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• The lining of the small intestine is folded and
covered with tiny, fingerlike villi
– Villi increase the absorptive surface
• Nutrients pass through the epithelium of the
villi and into the blood
– The blood flows to the liver
– The liver can store nutrients and convert them to
other substances the body can use
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INTERIOR OF INTESTINE
Blood vessel
with blood
en route to
the liver
Nutrient
absorption
Nutrient
absorption
Microvilli
Epithelial
cells
Lumen
Muscle
layers
Circular folds
Villi
Blood
capillaries
Lymph
vessel
EPITHELIAL
CELLS
Nutrient
absorption
INTESTINAL WALL
VILLI
Figure 21.10B
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21.11 The large intestine reclaims water
• Undigested
material passes
to the large
intestine, or
colon
Large
intestine
(colon)
End
of small
intestine
– Water is
absorbed
– Feces are
produced
Small
intestine
Rectum
Anus
Nutrient
flow
Appendix
Cecum
Figure 21.11
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DIETS AND DIGESTIVE ADAPTATIONS
21.12 Adaptations of vertebrate digestive systems
reflect diet
• Herbivores and omnivores generally have
longer alimentary canals than carnivores
– Plant matter is more difficult to digest than meat
– Nutrients in vegetation are less concentrated
than in meat
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Small intestine
Small
intestine
Stomach
Cecum
Colon
(large
intestine)
CARNIVORE
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HERBIVORE
Figure 21.12A
• Some mammals house cellulose-digesting
microbes in the colon or cecum
– The cecum is a pouch where the large and small
intestines connect
– Examples: horses and elephants
• Other mammals re-ingest their feces to recover
nutrients
– Examples: rabbits and some rodents
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• Ruminants such as cows process cellulose in a
four-chambered stomach
Intestine
3 Omasum
1 Rumen
Esophagus
Rumen
4 Abomasum
2 Reticulum
Figure 21.12B
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NUTRITION
21.13 Overview: A healthful diet satisfies three
needs
• An animal’s diet provides
– fuel for its activities
– raw materials for making the body’s own
molecules
– essential nutrients that the body cannot make
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21.14 Chemical energy powers the body
• Once nutrients are inside cells, they can be
oxidized by cellular metabolism to generate
energy
– This energy is in the form of ATP
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• The energy a resting
animal requires each
day to stay alive is its
basal metabolic rate
(BMR)
Figure 21.14
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• More energy is
required for an
active life
– Excess energy
is stored as
glycogen or
fat
Table 21.14
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21.15 Connection: Body fat and fad diets
• The human body tends to store excess fat
molecules instead of using them for fuel
• A balanced diet includes adequate amounts of
all nutrients
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• Fad diets are often ineffective and can be
harmful
Table 21.15
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21.16 Connection: Vegetarians must be sure to
obtain all eight essential amino acids
• The eight essential amino acids that adults
require must be obtained from food
– They are easily
obtained from
animal protein
ESSENTIAL
AMINO ACIDS
Methionine
Valine
– They can also be
obtained from the
proper combination
of plant foods
(Histidine)
Threonine
Phenylalanine
Corn
Leucine
Isoleucine
Tryptophan
Lysine
Figure 21.16
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Beans and
other
legumes
21.17 Connection: A healthful diet includes 13
vitamins
• Most of these vitamins function as coenzymes
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Table 21.17 (Water-soluble vitamins)
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Table 21.17 (Fat-soluble vitamins)
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21.18 Connection: Essential minerals are required
for many body functions
• Minerals are elements other than carbon,
hydrogen, oxygen, and nitrogen
– They play a variety of roles in the body
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Table 21.18
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21.19 Connection: What do food labels tell us?
• Food labels
provide
important
nutritional
information
about packaged
foods
Figure 21.19
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21.20 Connection: Diet can influence
cardiovascular disease and cancer
• Choice of diet may reduce the risk of
cardiovascular disease and cancer
BEHAVIORAL
RISK FACTORS
Fatty diet
UNAVOIDABLE
RISK FACTORS
High
blood
cholesterol
High
blood
pressure
Lack of
exercise
Aging
Family history
CARDIOVASCULAR
DISEASE
Smoking
Being male
Figure 21.20
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Table 21.20
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• A sound diet supplies
– enough raw materials to make all the
macromolecules we need
– the proper amounts of prefabricated essential
nutrients
– enough kilocalories to satisfy our energy needs
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