Download TX Bio Ch27

27
780
Animal
Systems I
FO
S ON
CU
TEKS
4B
(NEAR) DEATH BY
SALT WATER
Red-billed oxpeckers are carnivores
that have a mutualistic relationship with
zebras. These birds eat ticks and insects
that feed on the zebras, freeing them of
these parasites.
It started as an adventure. Some college buddies
tried their own version of a “survivor”
experience. During summer
vacation, they were dropped off
on an uninhabited tropical island,
with minimal supplies. They would
be picked up in a few days.
The island was hot and dry, and they
discovered that there was no fresh water. They knew that
coconuts could provide fluids in the form of coconut “milk.”
But one group member hated coconuts. He figured he’d
get his fluids by drinking salt water. At first, he was fine—
although he was thirstier than his friends. Then, he became
nauseated and weak. His condition worsened quickly. Soon
he was seriously ill—with dizziness, headaches, and an
inability to concentrate. His friends began to panic. What
was happening? As you read the chapter, look for clues to
help you explain the reason for the survivalist’s illness. Then,
solve the mystery.
Never Stop Exploring Your World.
Finding out what happened to the survivalist is only the
beginning. Take a video field trip with the ecogeeks of
Untamed Science to see where the mystery leads.
Texas Essential Knowledge and Skills
READINESS TEKS: 10A Describe the interactions that occur among systems
that perform the functions of regulation, nutrient absorption, reproduction, and
defense from injury or illness in animals. 12A Interpret relationships, including
predation, parasitism, commensalism, mutualism, and competition among
organisms.
SUPPORTING TEKS: 9C Identify and investigate the role of enzymes.
12B Compare variations and adaptations of organisms in different ecosystems.
TEKS: 3D Evaluate the impact of research on scientific thought, society, and the
environment. Also covered: TEKS 3B.
Animal Systems I 781
27.1
Feeding and Digestion
In this lesson you will learn about the various feeding relationships among animals (TEKS 12A), as well as the
interactions of various body systems during digestion and the absorption of nutrients (TEKS 10A). You will also learn
about the role of enzymes in digestion (TEKS 9C).
Key Questions
How does digestion occur
in animals?
THINK ABOUT IT From tiny insects that dine on our blood, to
bison that feed on prairie grasses, to giant blue whales that feed on
plankton, all animals are heterotrophs that obtain nutrients and energy
from food. Feeding adaptations are a large part of what makes animals
interesting.
How are mouthparts
adapted for different diets?
Obtaining Food
How do animals obtain
food?
Vocabulary
TEKS 12A
How do animals obtain food?
intracellular digestion
extracellular digestion
gastrovascular cavity
digestive tract
rumen
There’s an old saying that “You are what you eat.” We can rephrase
that as “How you look and act depends on what and how you eat.” In
formal biological language, evolutionary adaptations for feeding on
different foods in different ways have shaped the body structures and
adaptations of animals, such as those in Figure 27–1.
Taking Notes
Filter Feeders Filter feeders strain their food from water.
Most
filter feeders catch algae and small animals by using modified gills
or other structures as nets that filter food items out of water. Many
invertebrate filter feeders are small or colonial organisms, like worms
and sponges, that spend their adult lives in a single spot. Some vertebrate filter feeders, such as blue whales, are huge, and feed while
swimming.
Outline Before you read, use the
headings in this lesson to outline
the ways animals obtain and
digest food. As you read, add
details to your outline.
ELPS 4.G.3
Read with a partner the Key
Questions. As you read the lesson
together, work out some possible
responses to each Key Question.
Then, pair up with another group
of two. Ask one another the Key
Questions. Respond to the questions, using your notes.
BUILD Vocabulary
WORD Origins The word part
-vore comes from the Latin verb
vorare, which means “to devour.”
782
Detritivores Detritus is made up of decaying bits of plant and animal
Detritivores feed on detritus, often obtaining extra
material.
nutrients from the bacteria, algae, and other microorganisms that
grow on and around it. Detritivores are essential members of many
food webs.
Carnivores
Carnivores eat other animals. Mammalian carnivores, such as wolves, use teeth, claws, and speed or stealthy hunting
tactics to capture prey. Many carnivorous invertebrates would be as
menacing as tigers if they were larger. Some cnidarians paralyze prey
with poison-tipped darts, while some spiders immobilize their victims
with venomous fangs.
Herbivores
Herbivores eat plants or parts of plants or algae.
Leaves don’t have much nutritional content, are tough to digest, and
can contain poisons or hard particles that wear down teeth. Other herbivores specialize in eating seeds or fruits, which are often filled with
energy-rich compounds.
Nutritional Symbionts Recall that a symbiosis is the dependency of
one species on another. Symbionts are the organisms involved in a symbioMany animals rely upon symbiosis for their nutritional needs.
sis.
Parasitic Symbionts Parasites live within or on a host organism,
where they feed on tissues or on blood and other body fluids, disrupting the health of their hosts. Some parasites are just nuisances, but
many cause serious diseases in humans, livestock, and crop plants.
Parasitic flatworms and roundworms afflict millions of people, particularly in the tropics.
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Mutualistic Symbionts Mutualistic nutritional relationships benefit
both participants, and are often important in maintaining the health
of organisms. Reef-building corals depend on symbiotic algae that live
within their tissues for most of their energy. Those algae capture solar
energy, recycle nutrients, and help corals lay down calcium carbonate
skeletons. The algae, in turn, obtain nutrients from the corals’ wastes.
Many animals have close relationships with symbiotic microorganisms that live within their digestive tracts. Animals that eat wood
or plant leaves rely on microbial symbionts to break down cellulose,
which no animal can digest on its own. Recent research has shown
that microorganisms living in human intestines play vital roles in
maintaining health. These gut microorganisms help in digestion and
nutrient absorption, manufacture some essential vitamins, and help
protect the host from other potentially harmful microorganisms.

Carnivore – Orca
Filter Feeders – Barnacles
Figure 27–1 Obtaining Food
The orca, sea slug, barnacles, and
cleaner shrimp obtain their food in
different ways.
Herbivore – Sea Slug
Detritivore – Cleaner Shrimp
Animal Systems I 783
TEKS 2G, 9C
A scientist performed an experiment to determine
the amount of time needed for a certain carnivorous
animal to digest animal protein. He placed pieces of
hard-boiled egg white (an animal protein) in a test
tube containing ­hydrochloric acid, water, and the
enzyme pepsin, which digests protein. The graph
shows the rate at which the egg white was ­“digested”
over a 24-hour period.
1. Interpret Graphs Describe the trend in the amount
of protein digested over time.
2. Analyze Data About how many hours did it take
for half of the protein to be digested?
A
Sponge
B C D
E
F
Water
G HandI
wastes out
Percentage of
Egg White Digested
Protein Digestion
Rate of Digestion
100
80
60
40
20
0
0
4
8
12
16
20
24
Time (hours)
3. Draw Conclusions How would you
expect the rate of meat digestion to differ
in an animal whose digestive tract had less
of the enzyme pepsin?
Processing Food
TEKS 9C, 10A
How does digestion occur in animals?
Obtaining food is just the first step. Food must then be broken down,
or digested, and absorbed to make energy and nutrients available to
Some invertebrates break down food ­primarily
body tissues.
by intracellular digestion, but many animals use extracellular
digestion to break down food. A variety of digestive systems are
shown in Figure 27–2.
Incurrent Pore
Water and food
particles in
A
B Cnidarian
C D E
Intracellular Digestion Animals have evolved many ways of digesting and absorbing food. The simplest animals, such as sponges, digest
food inside specialized cells that pass nutrients to other cells by diffusion. This digestive process is known as intracellular digestion.
F
G
H
I
Extracellular Digestion Most more-complex animals rely on extracellular digestion. Extracellular digestion is the process in which food
is broken down outside cells in a digestive system and then absorbed.
Gastrovascular Cavities Some animals have an interior body space
with tissues that carry out digestive and circulatory functions. Some
invertebrates, such as cnidarians, have a gastrovascular cavity with a
single opening through which they both ingest food and expel wastes.
Some cells lining the cavity secrete enzymes and absorb diges­ted food.
Other cells surround food particles and digest them in vacuoles.
Nutrients are then transported to cells throughout the body.

Mouth/Anus
Digestive Tracts Many invertebrates and all vertebrates, such as
birds, digest food in a tube called a digestive tract, which has two
openings. Food moves in one direction, entering the body through
the mouth. Wastes leave through the anus.

Gastrovascular
cavity
784 Chapter 27 • Lesson 1
One-way digestive tracts often have specialized structures, such A
as a stomach and intestines, that perform different tasks as food
passes through them. You can think of a digestive tract as a kind
of “disassembly line” that breaks down food one step at a time. In
some animals, the mouth secretes digestive enzymes that start the
chemical digestion of food. Then, mechanical digestion may occur as
specialized mouthparts or a muscular organ called a gizzard breaks
food into small pieces. Then, chemical digestion begins or continues
in a stomach that secretes digestive enzymes. Chemical breakdown
continues in the intestines, sometimes aided by secretions from other
organs such as a liver or pancreas. Intestines also absorb the nutrients
released by digestion.
Solid Waste Disposal No matter how efficiently an animal breaks
down food and extracts nutrients, some indigestible material will always
be left. These solid wastes, or feces, are expelled either through the
single digestive opening or through the anus.

Specializations for
Different Diets TEKS 10A
How are mouthparts adapted for ­different diets?
The mouthparts and digestive systems of animals have evolved many
adaptations to the physical and chemical characteristics of different
foods, as shown in Figure 27–3. As a window into these specializations,
we’ll examine adaptations to two food types that are very different
physically and chemically: meat and plant leaves.
Specialized Mouthparts Carnivores and leaf-eating herbivores
usually have very different mouthparts. These differences are typically
related to the different physical characteristics of meat and plant leaves.
Carnivore
B
C Bird
D E
F
G
H
I
Mouth
Esophagus
Crop
Anus
Stomach
Gizzard
Intestine
Figure 27–2 Digesting Food
Animals have different digestive
structures with different functions.
E
G H I
A The
B sponge
C D(previous
Fpage)
has one digestive opening and
uses intracellular digestion to
process its food.
A B The
C cnidarian
D E
F G
(previous page) processes its
food by extracellular digestion in
A cavity.
B C The
D E
a gastrovascular
F G
bird has a one-way digestive tract
with two openings.
SPECIALIZED TEETH
Figure 27–3 Mouthparts The
specialized jaws and teeth of animals
are well adapted to their diets.
Canines Canines are pointed teeth.
Carnivores use them for piercing,
gripping, and tearing. In herbivores,
canines are reduced or absent.
Herbivore
Jaw joint
Jaw joint
Molars and Premolars The sharp edges
of these teeth slice and dice meat into
small pieces. These teeth have ridges
that interlock during chewing like the
blades of scissors.
Incisors Chisel-like incisors
are used for cutting,
gnawing, and grooming.
Molars and Premolars
Broad, flattened molars
and premolars are
adapted for grinding tough
plants, like two pieces of
sandpaper wearing down
wood.
Animal Systems I 785
Eating Meat
Carnivores typically have sharp mouthparts or other structures that can capture food, hold it, and
“slice and dice” it into small pieces. Carnivorous mammals,
such as wolves, have sharp teeth that grab, tear, and slice food like
knives and scissors would. The jaw bones and muscles of carnivores are adapted for up-and-down movements that chop meat
into small pieces.

Eating Plant Leaves
Herbivores have mouthparts adapted to rasping or grinding to tear plant cell walls and expose
their contents. Many herbivorous invertebrates, from mollusks to
insects, have mouthparts that grind and pulverize plant or algal
tissues. Herbivorous mammals, such as the horse in Figure 27–4,
have front teeth and muscular lips adapted to grabbing and pulling leaves, and flattened molars that grind leaves to a pulp. The
jaw bones and muscles of mammalian herbivores are also adapted
for side-to-side “grinding” movements.

figure 27–4 Eating Plant Leaves
The teeth and jaws of herbivores,
such as horses, are adapted for
pulling, rasping, and grinding
plant leaves.
Specialized Digestive Tracts Carnivorous invertebrates and
vertebrates typically have short digestive tracts that produce fast
acting, meat-digesting enzymes. These enzymes can digest most
cell types found in animal tissues.
No animal produces digestive enzymes that can break down
the cellulose in plant tissue, however. Some herbivores have very
long intestines or specialized pouches in their digestive tracts that
harbor microbial symbionts that help digest tough plant tissues
and help maintain the health of their hosts. Animals called ruminants, such as cattle, have a pouchlike extension of their esophagus called a rumen (plural: rumina), in which symbiotic bacteria
digest cellulose. Ruminants regurgitate food that has been partially
digested in the rumen, chew it again, and reswallow it. This process is called “chewing the cud.”
27.1 Review Key Concepts
TEKS 10A, 12A
1. a. Review What types of food do herbivores eat?
What are nutritional symbionts?
b. Relate Cause and Effect How might a coral be
affected if all its symbiotic algae died?
2. a. Review What are two types of digestion animals
use to break down and absorb food?
b. Compare and Contrast What is a major structural
difference between gastrovascular cavities and
digestive tracts?
3. a. Review Describe the adaptations of the mouthparts
and digestive systems of leaf-eaters and meat-eaters.
786 Chapter 27 • Lesson 1
b. Interpret Describe the relationship between a ruminant and its
microbial symbionts in terms
of “teamwork.”
Summary
4. Describe the process of a cow’s
digestion of grass, from the cow’s
uprooting of the grass to its
reswallowing of it. Use the terms
molar, rumen, symbiont, and cud.
27.2
Respiration
In this lesson you will learn about the processes of respiration and gas exchange in animals (TEKS 10A).
THINK ABOUT IT Cellular respiration requires oxygen and pro-
duces carbon dioxide as a waste product. So all animals must obtain
oxygen from their environment and get rid of carbon dioxide. In other
words, all animals need to “breathe.” Humans can drown because our
lungs can’t extract oxygen from water. Most fishes have the opposite
problem; out of water, their gills don’t work. How are these different
respiratory systems adapted to their different environments?
Gas Exchange
What characteristics do the respiratory structures of all
animals share?
Despite all the amazing things living cells can do, no cell can actively
pump oxygen or carbon dioxide across membranes. Yet, in order to
breathe, all animals must exchange oxygen and carbon dioxide with
their surroundings. How do they do it? One way that animals have
adapted to different environments is by evolving respiratory structures
that promote the movement of these gases in the required directions
by passive diffusion.
Gas Diffusion and Membranes Recall that substances diffuse from
an area of higher concentration to an area of lower concentration.
Gases diffuse most efficiently across a thin, moist membrane that is
permeable to those gases. The larger the surface area of that membrane, the more diffusion can take place, just as a bumpy paper towel
absorbs more liquid than a smooth one does. These physical principles
create a set of requirements that respiratory systems must meet, one
way or another.
Key Questions
What characteristics do
the respiratory structures of all
animals share?
How do aquatic animals
breathe?
What respiratory structures
enable land animals to breathe?
Vocabulary
gill • lung • alveolus
Taking Notes
Concept Map Draw a concept
map showing the characteris­
tics of the lung structures of
vertebrates.
Figure 27–5 Requirements for
Respiration Respiratory surfaces
are moist, so exhaled air contains
a lot of moisture. That exhaled
moisture condenses into visible
“fog“ if outside air is cold.
Requirements for Respiration Because
of the behavior of gases, all respiratory
systems share certain basic characterisRespiratory structures provide
tics.
a large surface area of moist, selectively
permeable membrane. Respiratory structures maintain a difference in the ­relative
concentrations of oxygen and carbon
dioxide on either side of the respiratory
membrane, promoting diffusion.
787
Operculum Water carrying
carbon dioxide is pumped
out behind the operculum, or
gill cover.
Gill Filaments
Mouth
A muscular
pump pulls
water in through
the mouth and
pushes it back
across the gills.
Water is pumped
past thousands of
threadlike gill
filaments, which are
rich with capillaries.
Filaments absorb
oxygen from water
and release carbon
dioxide.
Figure 27–6 Respiration With Gills Many
aquatic animals, such as fishes, respire with
gills, which are thin, selectively permeable
membranes. As water passes over the gills,
gas exchange is completed within the gill
capillaries.
Respiratory Surfaces
of Aquatic ­Animals
How do aquatic animals breathe?
Some aquatic invertebrates, such as cnidarians and some flatworms,
are relatively small and have thin-walled bodies whose outer surfaces
are always wet. These animals rely on diffusion of oxygen and carbon
dioxide through their outer body covering. A few aquatic chordates,
including lancelets, some amphibians, and even some sea snakes, rely
to varying extents on gas exchange by diffusion across body surfaces.
For large, active animals, however, skin respiration alone is not
Many aquatic invertebrates and most aquatic chorenough.
dates other than reptiles and mammals exchange gases through
gills. As shown in Figure 27–6, gills are feathery structures that
expose a large surface area of thin, selectively permeable membrane
to water. Inside the gill membranes is a network of tiny, thin-walled
blood vessels called capillaries. Many animals, including aquatic mollusks and fishes, actively pump water over their gills as blood flows
through inside. This helps maintain differences in oxygen and carbon
Aquatic reptiles
dioxide concentration that promote diffusion.
and aquatic mammals such as whales breathe with lungs and must
hold their breath underwater. Lungs are organs that exchange oxygen and carbon dioxide between blood and air. You will learn more
about lungs shortly.
TEKS 10A
Breathing in Clams and Crayfishes
5 clam
6 or7crayfish.
8 9Put a drop
Do2 not3touch
4 the
of food coloring in the water near a clam’s
­siphons. Observe what happens to the coloring.
1
1
6 coloring
7 8 9
2 Put
3 a drop
4 5of food
in the water
near the middle of a crayfish. CAUTION: Keep
your fingers away from the crayfish’s pincers.
Observe what happens to the coloring.
Analyze and Conclude
1. Observe Describe what happened to the
coloring in step 1. How does water move
through a clam’s gills?
788 Chapter 27 • Lesson 2
2. Infer What is the clam’s main defense? How
is the location of the clam’s siphons related to
this defense?
3. Compare and Contrast What happened in
step 2? Compare the flow of water through the
gills of clams and crayfishes.
4. Infer Unlike many other arthropods, crayfishes
have gills. Why do crayfishes need gills?
Insect
Spider
Tracheal tubes
Airflow
Spiracles
Book lung
Spiders respire using organs called
book lungs, which are made of
parallel, sheetlike layers of thin
tissues that contain blood vessels.
Respiratory Surfaces
of Terrestrial Animals
In most insects, a system of tracheal tubes extends
throughout the body. Air enters and leaves the system
through openings in the body surface called spiracles.
In some insects, oxygen and carbon dioxide diffuse
through the tracheal system, and in and out of body
fluids. In other insects, body movements help pump air
in and out of the tracheal system.
Figure 27–7 Respiratory Structures
TEKS 10A
What respiratory structures enable land animals
to breathe?
Terrestrial animals must keep their respiratory membranes
moist in dry environments. They must also carry oxygen and
carbon dioxide back and forth between those surfaces and the
rest of their bodies. Interactions among several body systems
are essential for this process.
of Terrestrial Invertebrates Terrestrial
invertebrates have a wide variety
of respiratory structures, including
skin, mantle cavities, book lungs,
and tracheal tubes. These structures
must stay moist even in the driest of
conditions in order to function properly.
Respiratory Surfaces in Land Invertebrates The many
body plans found among terrestrial invertebrates include very
different strategies for respiration.
Respiratory structures
in terrestrial invertebrates include skin, mantle cavities, book
lungs, and tracheal tubes. Some land invertebrates, such as
earthworms, live in moist environments and can respire across
their skin if it stays moist. Other invertebrates, such as land
snails, respire using a mantle cavity lined with moist tissue and
blood vessels. Insects and spiders have more complex respiratory systems, as you can see in Figure 27–7.
Lung Structure in Vertebrates Terrestrial vertebrates display
But all terrestrial
a wide range of breathing adaptations.
vertebrates—reptiles, birds, mammals, and the land stages
of most amphibians—breathe with lungs. Although lung
structure in these animals varies, the processes of inhaling and
exhaling are similar. Inhaling brings oxygen-rich air through
the trachea (tray kee uh), or airway, into the lungs. Inside the
lungs, oxygen diffuses into the blood through lung capillaries.
At the same time, carbon dioxide diffuses out of capillaries into
the lungs. Oxygen-poor air is then exhaled.
Online Journal Would you expect dolphins to
breathe with gills or lungs? Explain your answer.
BUILD Vocabulary
Multiple Meanings The biological
term respiration has different, though
related, meanings. In animals, it can
refer to gas exchange, the intake
of oxygen and release of waste
gases, or to cellular respiration, the
cell process that releases energy by
breaking down food molecules in the
presence of oxygen. Because cellular
respiration requires oxygen, the two
processes are related.
Animal Systems I 789
Nostrils, mouth, and throat
Trachea
Lung
Figure 27–8 Lungs Terrestrial
vertebrates breathe with lungs.
Lungs with a larger surface area can
take in more oxygen and release
more carbon dioxide. Mammals have
the greatest lung surface area among
animals. Infer Why do mammals
require a large surface area with
which to process oxygen?
Amphibian
Reptile
Mammal
Amphibian, Reptilian, and Mammalian Lungs The internal
surface area of lungs increases from amphibians to reptiles to mammals, as shown in Figure 27–8. A typical amphibian lung is little more
than a sac with ridges. Reptilian lungs are often divided into chambers
that increase the surface area for gas exchange. Mammalian lungs
branch extensively, and air passages branch and re-branch, ending in
bubblelike structures called alveoli (al vee uh ly; singular: alveolus).
Alveoli provide an enormous surface area for gas exchange. Alveoli
are surrounded by a network of capillaries in which blood picks up
oxygen and releases carbon dioxide. Mammalian lung structure helps
take in the large amounts of oxygen required by high metabolic rates.
When mammals and most other vertebrates breathe, air moves in and
out through the same air passages, and some stale, oxygen-poor air
remains. In humans, this stale air is typically equivalent to about one
third of the air inhaled in a normal breath.

 Bird Lungs In birds, the lungs are structured so that air flows mostly
in only one direction. No stale air gets trapped in the system. A unique
system of tubes and air sacs in birds’ respiratory systems enables this
one-way airflow. Thus, gas exchange surfaces are continuously in contact with fresh air. This highly efficient gas exchange helps birds obtain
the oxygen they need to power their flight muscles at high altitudes for
long periods of time.
27.2
Review Key Concepts
1. a. Review In what ways are the respiratory
structures of all animals similar?
b. Apply Concepts Explain why it is important that ­respiratory surfaces are moist and
permeable.
2. a. Review Which groups of aquatic animals
breathe with gills? With lungs?
b. Relate Cause and Effect Why do some animals actively pump water over their gills?
3. a. Review How do terrestrial invertebrates and
terrestrial vertebrates breathe?
790 Chapter 27 • Lesson 2
b. Interpret Visuals Contrast the structures of
amphibian, reptilian, and mammalian lungs,
as shown in Figure 27–8.
Description
4. Describe the events that occur when a
mammal respires, ­including the path of air
through its lungs.
27.3
Circulation
In this lesson you will learn about the process of circulation in animals.
Think About It When you eat food, your digestive tract breaks
it down. But how do energy and nutrients from food get to your
cells? How does oxygen from your lungs get to other tissues? How
do carbon dioxide and wastes get eliminated? Some aquatic animals
with bodies only a few cells thick rely solely on diffusion to transport
materials. But in most animals, oxygen, carbon dioxide, nutrients,
and wastes are transported through a circulatory system that interacts with other body systems.
Open and Closed
Circulatory ­Systems
How do open and closed circulatory systems compare?
Many animals move blood through their bodies using one or more
hearts. A heart is a hollow, muscular organ that pumps blood
around the body. A heart can be part of either an open or a closed
circulatory system.
Open Circulatory Systems Arthropods and most mollusks
have open circulatory systems, such as the one in Figure 27–9.
In an open circulatory system, blood is only partially
contained within a system of blood vessels as it travels through
the body. One or more hearts or heartlike organs pump blood
through vessels that empty into a system of sinuses, or spongy
cavities. There, blood comes into direct contact with body tissues. Blood then collects in another set of sinuses and eventually
makes its way back to the heart.
Key Questions
How do open and closed
circulatory systems compare?
How do the patterns of
circulation in vertebrates
compare?
Vocabulary
heart
open circulatory system
closed circulatory system
atrium
ventricle
Taking Notes
Cycle Diagram As you read,
draw a cycle diagram showing
a five-step sequence in which
blood pumps through a closed,
two-loop circulatory system.
Hearts
Figure 27–9 Open Circulatory
Blood
vessels
Insect: Open
Circulatory System
Heart
System In an open circulatory system,
blood is not entirely contained within blood
vessels. Grasshoppers, for example, have
open circulatory systems in which blood
leaves vessels and moves through sinuses
before returning to a heart.
Sinuses
and organs
791
Figure 27–10 Closed Circulatory
System Annelids, such as earthworms,
and many more-complex animals
have closed circulatory systems. Blood
stays within the vessels of a closed
circulatory system.
Heartlike
structure
Small vessels
in tissues
Closed Circulatory Systems Many larger, more active ­invertebrates,
including annelids and some mollusks, and all vertebrates, have
closed circulatory systems, such as the one shown in Figure 27–10.
In a closed circulatory system, blood circulates entirely within
blood vessels that extend throughout the body. A heart or heartlike
organ forces blood through these vessels. Nutrients and oxygen reach
body tissues by diffusing across thin walls of capillaries, the smallest
blood vessels. Blood that is completely contained within blood vessels can be pumped under higher pressure, and thus can be circulated
more efficiently, than can blood in an open system.
Single- and Double-Loop
Circulation
How do the patterns of circulation in vertebrates compare?
Annelid: Closed
Heartlike Blood
Circulatory System structures vessels
BUILD Vocabulary
Multiple meanings The word
atrium has different but parallel
meanings in everyday usage and
in biology. In everyday usage, it
means a large entrance hall. In
biology, it means a heart chamber
through which blood from the body
enters the heart.
As chordates evolved, they developed more-complex organ systems
and more-efficient channels for internal transport. You can see two
main types of circulatory systems of vertebrates in Figure 27–11.
Single-Loop Circulation
Most vertebrates with gills have a
single-loop circulatory system with a single pump that forces blood
around the body in one direction. In fishes, for example, the heart
consists of two chambers: an atrium and a ventricle. The atrium ­(plural:
atria) receives blood from the body. The ventricle then pumps blood
out of the heart and to the gills. Oxygen-rich blood then travels from
the gills to the rest of the body and returns, oxygen-poor, to the atrium.
Double-Loop Circulation As terrestrial vertebrates evolved into larger
and more active forms, their capillary networks became larger. Using a
single pump to force blood through the entire system would have been
increasingly difficult. This issue was avoided as the lineage of vertebrates
Most vertethat led to reptiles, birds, and mammals evolved.
brates that use lungs for respiration have a double-loop, two-pump
circulatory system.
Gill capillaries
Lung capillaries
Figure 27–11 Single- and
Double-Loop Circulation
Most vertebrates that use
gills for respiration have a
single-loop circulatory system
that forces blood around the
body in one direction (left).
Vertebrates that use lungs have
a double-loop system (right).
(Note that in diagrams of
animals’ circulatory systems,
blood vessels carrying oxygenrich blood are red, while blood
vessels carrying oxygen-poor
blood are blue.)
792 Chapter 27 • Lesson 3
1 ventricle
2 atria
Heart
1 atrium
Heart
2 ventricles
Body capillaries
Body capillaries
The first loop, powered by one side of the heart, forces oxygenpoor blood from the heart to the lungs. After the blood picks up
oxygen (and drops off carbon dioxide) in the lungs, it returns to the
heart. Then, the other side of the heart pumps this oxygen-rich blood
through the second circulatory loop to the rest of the body. Oxygen-poor
blood from the body returns to the heart, and the cycle begins again.
Mammalian Heart-Chamber Evolution Four-chambered hearts
like those in modern mammals are actually two separate pumps working next to one another. But where did the second pump come from?
During chordate evolution, partitions evolved that divided the original two chambers into four. Those partitions transformed one pump
into two parallel pumps. The partitions also separated oxygen-rich
blood from oxygen-poor blood. We can get an idea of how the partitions evolved by looking at other modern vertebrates.
Amphibian hearts usually have three chambers: two atria and
one ventricle. The left atrium receives oxygen-rich blood from the
lungs. The right atrium receives oxygen-poor blood from the body.
Both atria empty into the ventricle. Some mixing of oxygen-rich and
­oxygen-poor blood in the ventricle occurs.
However, the internal structure of the
ventricle directs blood flow so that most
oxygen-poor blood goes to the lungs, and
most oxygen-rich blood goes to the rest of
the body.
Reptilian hearts typically have three
chambers. However, most reptiles have a
partial partition in their ventricle. Because
of this partition, there is even less mixing
of oxygen-rich and oxygen-poor blood
than there is in amphibian hearts.
27.3
Figure 27–12 Reptilian Heart
Under the armor-like hide of this
crocodile lies a heart with two
atria and one ventricle.
Review Key Concepts
1. a. Review Describe an open circulatory system. Describe a
closed circulatory system.
b. Explain Which groups of animals tend to have each type of
circulatory system?
c. Relate Cause and Effect How does having a closed circulatory
system benefit a large, active animal?
2. a. Review What are two different patterns of circulation found
in vertebrates?
b. Compare and Contrast What is the major structural difference between vertebrates that have single-loop circulatory
systems and those that have double-loop systems?
3. Infer Do you think large,
active vertebrates could
have evolved with open
circulatory systems?
Explain your reasoning.
Animal Systems I 793
27.4
Excretion
In this lesson you will learn how various animals get rid of wastes and how the excretory system interacts with other
body systems (TEKS 10A). In addition, you will learn about the various adaptations that have developed for the process
of excretion in different environments (TEKS 12B).
Key Questions
How do animals eliminate
toxic nitrogenous waste?
What adaptations enable
organisms in aquatic ecosystems
to eliminate wastes?
What adaptations enable
animals in terrestrial ecosystems
to eliminate wastes while conserving water?
Vocabulary
excretion • kidney •
nephridium • Malpighian tubule
Taking Notes
Preview Visuals Note three
questions you have about
­Figure 27–15. As you read, try
to answer your questions.
THINK ABOUT IT The first three lessons in this chapter discussed
respiratory and digestive systems that exchange gases, absorb nutrients
and get rid of indigestible waste. But cellular metabolism generates other
kinds of wastes that are released into body fluids and that must be eliminated from the body. What are these wastes and how do animals get rid of
them? The answers involve interactions between the digestive, respiratory,
and circulatory systems, and an excretory system that eliminates wastes.
The Ammonia Problem
TEKS 10A
How do animals eliminate toxic nitrogenous waste?
When cells break down proteins, they produce a nitrogen-containing,
or nitrogenous, waste: ammonia. This is a problem, because ammonia is poisonous! Even moderate concentrations of ammonia can kill
most cells. Animal systems address this difficulty in one of two ways.
Animals either eliminate ammonia from the body quickly or
convert it into other nitrogenous compounds that are less toxic. The
elimination of metabolic wastes, such as ammonia, is called excretion.
Some small animals that live in wet environments rid their bodies of
ammonia by allowing it to diffuse out of their body fluids across their
skin. Most larger animals, and even some smaller ones that live in
dry environments, have excretory systems that process ammonia and
eliminate it from the body.
Storing Nitrogenous Wastes Animals that cannot
dispose of ammonia as it is produced have evolved ways
to hold, or “store,” nitrogenous wastes until they can be
eliminated. In most cases, ammonia is too toxic to be
stored in body fluids. Insects, reptiles, and birds typically solve this problem by converting ammonia into a
sticky white compound called uric acid, which you can
see in Figure 27–14. Uric acid is much less toxic than
ammonia and is also less soluble in water. Mammals
and some amphibians, on the other hand, convert
ammonia to a different nitrogenous compound—urea.
Like uric acid, urea is less toxic than ammonia, but
unlike uric acid, urea is highly soluble in water.
figure 27–13 Ammonia Some aquatic animals,
such as this zebra flatworm, release ammonia as
soon as they produce it.
794
Maintaining Water Balance Getting rid of any type of nitrogenous
waste involves water. For that reason, excretory systems interact with
other systems involved in regulating water balance in blood and body
tissues. In some cases, excretory systems eliminate excess water along
with nitrogenous wastes. In other cases, excretory systems must eliminate nitrogenous wastes while conserving water.
Many animals use kidneys to separate wastes and excess water
from blood in a fluid called urine. Kidneys must perform this function despite a serious limitation: No living cell can actively pump
water across a membrane. You may recall that cells can pump ions
across their membranes. Kidney cells pump ions from dissolved salts
in blood in ways that create an osmotic gradient. Water then “follows”
those ions passively by osmosis. This process can get rid of nitrogenous wastes and retain water, but leaves kidneys with one weakness:
They usually cannot excrete excess salt.
Figure 27–14 Other Nitrogenous
Compounds Many animals, like
these seagulls, convert ammonia
to uric acid and excrete it as sticky
white guano.
Online Journal Explain how kidneys remove excess water
from the blood.
Excretion in Aquatic Animals
TEKS 12B
What adaptations enable organisms in aquatic ecosystems to
eliminate wastes?
Aquatic animals have an advantage in getting rid of nitrogenous wastes
In general, aquatic animals
because they are surrounded by water.
can allow ammonia to diffuse out of their bodies into surrounding
water, which dilutes the ammonia and ­carries it away. But aquatic
animals still face excretory challenges. Many have adaptations that
either eliminate water from their bodies or conserve it, depending on
whether they live in fresh or salt water ecosystems, as summarized in
Figure 27–15 on the next page.
Animal Systems I 795
S
alt
te
Wa
Ur
in
r
More salt
Less water
e
l
Sa
W
at
er
Don
’t dr
Fresh Water
More water
Less salt
t
ink
The bodies of freshwater animals, such
as fishes, contain a higher concentration of salt than the water they live in.
So they excrete water through kidneys
that produce lots of watery urine. They
don't drink, and they actively pump salt
in across their gills.
e
at
W
Salt
r
More water
Less salt
Ur
in
EXCRETION IN AQUATIC
ANIMALS
Figure 27–15 All animals must
rid their bodies of ammonia while
maintaining appropriate water
balance. Freshwater and saltwater
animals face very different
challenges in this respect.
Interpret Visuals What are two
ways freshwater fishes avoid
looking like “water balloons with
eyes”?
So they lose water through osmosis,
and salt diffuses in. If they didn’t
conserve water and eliminate salt,
they’d shrivel up like dead leaves.
e
The bodies of saltwater animals, such
as fishes, contain a lower concentration
of salt than the water they live in.
Salt
W
ate
r
n
Do dri
Salt Water
Less water
More salt
So water moves into their bodies by
osmosis, mostly across the gills. Salt
diffuses out. If they didn’t excrete water,
they’d look like water balloons with
eyes!
k
So they conserve water by producing
very little concentrated urine. They
drink, and they actively pump salt out
across their gills.
Freshwater Animals Many freshwater invertebrates lose ammonia to
their environment by simple diffusion across their skin. Many freshwater fishes and amphibians eliminate ammonia by diffusion across the
same gill membranes they use for respiration.
But invertebrates and fishes that live in freshwater must excrete
wastes while managing an osmotic challenge. The concentration
of water surrounding their bodies is higher than the concentration of
water in their body fluids. So water moves passively into their bodies by
osmosis, and salt leaves by diffusion. To help maintain water balance,
flatworms have adaptations involving specialized cells called flame cells
that remove excess water from body fluids. That water travels through
excretory tubules and leaves through pores in the skin. Adaptations in
amphibians and freshwater fishes typically involve excreting excess water
in very dilute urine, and pumping salt actively inward across their gills.
Saltwater Animals Marine invertebrates and vertebrates typically
release ammonia by diffusion across their body surfaces or gill membranes. Many marine invertebrates have body fluids with water concentrations similar to that of the seawater around them. For that reason,
these animals have less of a problem with water balance than do freshwater invertebrates. Marine fishes, however, tend to lose water to their
surroundings because their bodies are less salty than the water they live
in. These animals actively excrete salt across their gills. Their kidneys
also produce small quantities of very concentrated urine—an adaptation that conserves water.
796 Chapter 27 • Lesson 4
Excretion in Terrestrial Animals
TEKS 12B
What adaptations enable animals in terrestrial ecosystems to
eliminate wastes while conserving water?
Land animals also face challenges. In dry environments, they can lose large
amounts of water from respiratory membranes that must be kept moist. In
addition, they must eliminate nitrogenous wastes in ways that require
disposing of water—even though they may not be able to drink water.
Figure 27–16 shows the excretory systems of some terrestrial animals.
TEKS 12B
Water and Nitrogen
Excretion
5 6
Urea7 8
1 Label
2 one
3 test
4 tube
and the other Uric Acid. Place
2 grams of urea in the one
labeled Urea. Place 2 grams
of uric acid in the one labeled
Uric Acid.
Terrestrial Invertebrates
Some terrestrial invertebrates,
including annelids and mollusks, produce urine in nephridia.
Nephridia (singular: nephridium) are tubelike excretory structures
that filter body fluid. Typically, body fluid enters the nephridia through
openings called nephrostomes and becomes more concentrated as it
to each
6 7
8 9
1 2 Add
3 154 mL5of water
moves along the tubes. Urine leaves the body through excretory pores.
test tube. Stopper and shake
Other terrestrial invertebrates, such as insects and arachnids,
the test tubes for 3 minutes.
convert ammonia into uric acid. Nitrogenous wastes, such as uric acid,
6 test
7 tube.
8 9
1 2 3 Observe
4 5 each
are absorbed from body fluids by structures called Malpighian tubules.
Record
your
observations.
These wastes are added to digestive wastes traveling through the gut. As
Analyze and Conclude
water is absorbed from these wastes, they crystallize and form a thick
paste, which leaves the body through the anus. This paste contains little
1. Observe Which
water, so these adaptations minimize water loss.
substance—urea or uric
acid—is less soluble in
Terrestrial Vertebrates In terrestrial vertebrates, excretion is carwater? Explain.
Mammals and land amphibians
ried out mostly by the kidneys.
2. Infer Reptiles excrete
­convert ammonia into urea, which is excreted in urine. In most
nitrogenous
wastes in the
­reptiles and birds, ammonia is converted into uric acid. Reptiles and
form of uric acid. How does
birds pass uric acid through ducts into a cavity that also receives digesthis adaptation help reptiles
tive wastes from the gut. The walls of this cavity absorb most of the
survive on land?
water from the wastes, causing the uric acid to separate out as white
crystals. The result is a thick, milky-white paste that you would recognize as “bird droppings.”
Nephrostome
Excretory
pore
Arthropod
Malpighian
tubules
Kidneys
Figure 27–16 Excretion in
Terrestrial Animals Some terrestrial
Nephridia
Annelid
invertebrates, such as annelids, rid
their bodies of ammonia by releasing
urine created in their nephridia (left).
Some insects and arachnids have
Malpighian tubules, which absorb uric
acid from body fluids and combine
it with digestive wastes (above). In
vertebrates, such as humans, excretion is
carried out mostly by the kidneys (right).
Bladder
Urethra
Vertebrate
Animal Systems I 797
9
Adaptations to Extreme Environments The kidneys of most terrestrial vertebrates are remarkable organs, but the way they operate
results in some limitations. Most vertebrate kidneys, for example,
cannot excrete concentrated salt. That’s why most vertebrates cannot
survive by drinking seawater. All that extra salt would overwhelm the
kidneys, and the animal would die of dehydration. Some marine reptiles and birds, such as the petrel in Figure 27–17, have evolved adaptations in the form of specialized glands in their heads that excrete
very concentrated salt solutions. Another excretory adaptation is
found in the kangaroo rats of the American southwest. The kidneys of
these desert rodents produce urine that is 25 times more concentrated
than their blood! In addition, their intestines are so good at absorbing
water that their feces are almost dry.
Figure 27–17 Excretion
Adaptations Some terrestrial animals
that must drink salt water, such as
this petrel, have evolved special
adaptations to excrete excess salt.
Specialized salt glands produce a
concentrated salt solution, which can
sometimes been seen dripping out of
their elongated nostrils.
27.4
Review Key Concepts
1. a. Review Why does the metabolic waste
ammonia pose a problem for all animals?
b. Explain How do insects, reptiles, and birds
eliminate ammonia? How do mammals and
some amphibians eliminate it?
c. Apply Concepts How do kidneys help maintain homeostasis while processing nitrogenous
wastes?
2. a. Review In general, how do aquatic animals
address the ammonia problem?
b. Compare and Contrast How do the differing
water balance needs of freshwater animals and
saltwater animals explain the difference in their
excretion of nitrogenous wastes?
798 Chapter 27 • Lesson 4
TEKS 4B, 12B
3. a. Review In what form do (a) annelids and
mollusks, (b) insects and arachnids, (c) mammals and land amphibians, and (d) reptiles and
birds excrete nitrogenous wastes?
b. Relate Cause and Effect Explain how differing
water balance needs relate to an animal’s conversion of ammonia to either urea or uric acid.
4. The Greek word ouron, meaning “urine,” has
led to the root uro-, of urea and uric (acid). Why
is it appropriate that these two words are each
formed from a root word meaning “urine”?
TEKS 3B, 3D
Testing for Heart Disease
Ever-improving imaging techniques make it possible for doctors to diagnose heart disease and
disorders quickly and without the risk of invasive
procedures. None of these tests involves ­inserting
instruments into the body, but they ­reveal the inner
workings of the heart with remarkable accuracy.
Computed Tomography Angiography
A patient is injected with an iodine-based dye.
Then the CT scanner rotates over the patient
and takes multiple X-rays of the heart, which a
computer uses to form three-dimensional images.
The test can show if parts of blood vessels are
blocked or damaged. The results can be used to
determine what further tests are needed or as a
guide for planning surgery.
Find two published journal articles
about one of the techniques mentioned. In a couple
of paragraphs, communicate your findings.
Echocardiography
High-frequency sound waves, transmitted
through the chest, are fed into a computer,
which analyzes the “echoes” to produce moving
images of the heart. This is an especially safe
test because it doesn’t involve radiation or dyes.
The test allows doctors to see the heart in action.
It can reveal an enlarged heart, reduced pumping action, and structural problems.
Magnetic Resonance Imaging (MRI)
MRI uses powerful magnets to ­produce images
that are particularly good for examining muscle
and other soft tissue. Professionals analyzing
MRI images can see the difference between
healthy tissue and unhealthy tissue. MRI does
not involve radiation or iodine-based dyes. It
can be used to assess heart muscle damage
caused by a heart ­attack, birth defects, or abnormal growths.
Technology and Biology 799
AP
E
Y TH
PL
TEKS
4B
(Near) Death by Salt water
Luckily, the pick-up the group arranged arrived earlier than
planned. They rushed the sick man to a hospital, where he
was diagnosed with severe dehydration and given
water and intravenous fluids. If he had gone
much longer without treatment, doctors told
his friends, he would have died. What had
happened? Why didn’t his friends suffer the
same problems?
As sailors have known for centuries, humans
can’t drink seawater for any length of time. But
why can’t we drink seawater?
Because seawater is saltier than human blood and body
fluids, drinking it loads the body with excess salt. Human
kidneys cannot produce urine with salt concentrations high
enough to get rid of that salt efficiently. So the kidneys are
forced to excrete more water in urine than the amount of salt
water consumed. Cells and tissues begin to dehydrate, and
fatal kidney failure can result.
1. Explain Why did the castaway who drank salt
water become dehydrated quicker than his fellow
“survivors?”
2. Infer Human blood needs to circulate through
very small capillaries. What might happen if the
water content of a person’s blood were to drop too
low?
3. Explain Using terms such as osmosis and diffu-
sion, explain why your cells and tissues would
dehydrate quickly if you were flooding your body
with salt water by drinking it.
4. Propose a Solution If you were marooned on
an island that had no fresh water, what would be
your plan for getting some?
800 Chapter 27 • Solve the Chapter Mystery
5. Compare and Contrast While the group mem-
ber who drank seawater became seriously ill, the
other group members experienced some water
stress as well. In general, what was going on in
their circulatory and excretory systems, and why
was it not as serious?
6. Investigate Although humans can’t safely drink
salt water and can’t exist without fresh water,
many marine birds and reptiles can do either or
both. Using the Web, research the different strategies other animals use to regulate salt content and
water balance.
27
TEKS Practice
Review Content
1. Animals that obtain food by ingesting decaying
bits of plant and animal material are called
a. herbivores.
c. detritivores.
b. carnivores.
d. filter feeders.
2. Algae that live in the bodies of reef-building
corals are
a. parasitic symbionts.
b. mutualistic symbionts.
c. occupants that have no effect on the coral
animals.
d. consumed as food by the coral animals.
3. In order for the exchange of oxygen and carbon
dioxide to take place, an animal’s respiratory
­surfaces must be kept
a. cold.
c. hot.
b. dry.
d. moist.
4. In a closed circulatory system, blood
a. comes in direct contact with tissues.
b. remains within blood vessels.
c. empties into sinuses.
d. does not transport oxygen.
5. Most chordates that have gills for respiration
have a(n)
a. double-loop circulatory system.
b. accessory lung.
c. single-loop circulatory system.
d. four-chambered heart.
6. The composition and levels of body fluids in
mammals are controlled by the
a. lungs.
c. intestine.
b. kidneys.
d. heart.
7. The elimination of metabolic wastes from the
body is called
a. excretion.
b. circulation.
c. respiration.
d. digestion.
Understand Concepts
8. Compare the processes of intracellular and extracellular digestion.
9. Describe the differences between the canine
and molar teeth of herbivorous and carnivorous
mammals.
TEKS 10A, 10C, 11A, 12B
10. How do vertebrate filter feeders obtain food?
11. With what respiratory structures do aquatic
r­ eptiles and aquatic mammals breathe? What
inconvenience does this cause when they are
­underwater?
12. Describe the circulatory system of a mammal as
open or closed, and state the number of loops and
the number of heart chambers.
13. Compare single-loop circulation and double-loop
circulation.
14. Why do most animals convert ammonia into urea
or uric acid?
15. What is the difference in kidney function of fresh-
water fishes and saltwater fishes?
Think Critically
16. Classify You are observing an animal that has a
digestive tract. Does this animal practice intracellular digestion or extracellular digestion? Explain
your answer.
17. Pose Questions Hummingbirds eat high-energy
foods, such as nectar. Many ducks eat insects and
other small animals. What are some research
questions you could investigate to discover more
about the diet of a bird species and its ­energy
needs?
18. Describe Describe the interactions that occur
among systems that perform the function of nutrient absorption in animals.
19. Predict During heavy rains, earthworms often
emerge from their burrows. What might happen
to an earthworm if it does not return to its burrow
when the rain stops and the air becomes dry?
20. Infer Land snails have a respiratory structure
called a mantle cavity, which is covered with mucus. What might the purpose of the mucus be?
21. Apply Concepts How do the interactions between a fish’s respiratory and circulatory systems
work together to maintain homeostasis in the
body as a whole?
22. Describe In what way do the digestive and respiratory systems depend on the circulatory system
to carry out the functions of obtaining nutrients?
801
REV
E
TEKS Practice
IEW TH
TEKS
Biology Chapter 27
23. Relate How do the lungs work together with the
circulatory system? Relate the levels of organization in biological systems to each other.
24. Infer The excretory systems of terrestrial inverte-
brates, such as earthworms, convert ammonia to
less toxic substances. Explain why this change is
unnecessary in small aquatic invertebrates, such
as planarians.
25. Apply Concepts Of all the nitrogenous wastes
eliminated by animals, uric acid requires the least
water to excrete. Why is the production of uric
acid an advantage to animals that live on land?
Use Science Graphics
A student conducts an experiment to measure the
effect of caffeine on the heart rate of a small pondwater crustacean called Daphnia. The heart of this animal is visible through its transparent shell. With the
help of a dissecting microscope, the student counts the
heartbeats per minute before and after adding increasing amounts of coffee to the water surrounding the
animal. Each data point in the graph at the top right
represents the average of five trials. Use the graph to
answer questions 26 and 27.
Heart Rate (beats per minute)
Daphnia Heart Rate and Caffeine
190
180
Daphnia
170
Heart Rate and Caffeine
160
Lesson 1
In Lesson 27.1, you learned about the different
ways that animals obtain nutrients. Once an
animal obtains food, that food must be digested
by either intracellular digestion or extracellular
digestion. Animals have mouthparts and digestive
systems that are adapted to the foods that they eat.
Readiness TEKS: 10A, 12A
Supporting TEKS: 9C
Lesson 2
In Lesson 27.2, you learned about the process
of respiration in animals. All animals, regardless
of how they get oxygen, must have respiratory
structures with a large surface area. Respiratory
structures must be kept moist and must have
membranes that permit the diffusion of oxygen and
carbon dioxide.
Readiness TEKS: 10A
Lesson 3
Lesson 27.3 discusses the circulatory system. The
circulatory system transports nutrients from the
digestive system and oxygen from the respiratory
system to body cells. Animals have either an
open circulatory system or a closed circulatory
system. In an open circulatory system, the blood
is only partially contained within blood vessels. In
a closed circulatory system, the blood is entirely
contained within blood vessels.
150
140
Lesson 4
130
120
0
0
1
2
3
4
5
Drops of Coffee Added
26. Interpret Graphs Describe the effect of caffeine
on the heart rate of Daphnia.
27. Predict What would be your prediction of the
effect of five or more drops of coffee on the heart
rate of Daphnia?
802 Chapter 27 • TEKS Practice
In Lesson 27.4, you learned about the excretory
system. Animals must eliminate ammonia from the
body quickly in order to maintain homeostasis.
Aquatic animals allow ammonia to diffuse out of
their bodies into the surrounding water. Terrestrial
animals have various adaptations to release
ammonia.
Readiness TEKS: 10A
Supporting TEKS: 12B
★ TEKS Practice: Chapter Review
1
Most animals have a circulatory system that moves blood around the body. Circulatory
systems can be categorized as open circulatory systems or closed circulatory systems. How
are these two categories of circulatory systems similar?
A Both can be double-loop or single-loop.
B Both have blood contained in blood vessels.
C Both deliver nutrients and oxygen by diffusion through capillary walls.
D None of the above
2
In animals, the excretory system rids the body of wastes produced by body tissues. The
graphic organizer below lists information about how the excretory system functions to
maintain homeostasis in a salt water animal.
Salt actively transported
through gills
Aquatic
Animal
Concentrated urine is
excreted to conserve water
Ammonia diffuses
through skin
What is a limitation of this graphic organizer?
F
It can be used to learn about water balance but not salt balance.
G It can be used to learn about salt balance but not water balance.
H It can be used to learn about saltwater animals but not freshwater animals.
J
It can be used to learn about freshwater animals but not saltwater animals.
Animal Systems I 803
3
The figure shows the skulls of two different mammals.
Incisors
Mammal 1
Canines
Mammal 2
Molars and premolars
Which observation provides the best evidence to support the explanation that Mammal 1
and Mammal 2 do not compete with one another for food?
A Mammals 1 and 2 have canines that differ in shape.
B Mammals 1 and 2 both have canines, incisors, molars, and premolars.
C Mammals 1 and 2 have incisors that are in the same location within the mouth.
D Mammals 1 and 2 have similar numbers of molars and premolars.
4
Animals do not produce enzymes that can digest cellulose, which is found in leaves and
wood. Some animals, such as termites and cows, can obtain nutrients from cellulose due to
the enzymes produced by other organisms that live in their digestive systems. The organisms
in the cow and termite digestive systems also benefit from the relationship. What is the best
classification for these relationships.
F
Competition
G Parasitism
H Mutualism
J
Predation
804 Chapter 27 • TEKS Practice
★ TEKS Practice: Cumulative Review
5
In Arctic food chains, elephant seals are prey of killer whales. Which body systems would
most directly enable an elephant seal to notice and swim away from a killer whale?
A Muscular, skeletal, and nervous systems
B Circulatory and excretory systems
C Digestive and nervous systems
D Skeletal and reproductive systems
6
The figure shows relationships among different organisms.
Allosaurs
Compsognathids
Tyrannosaurs
(T. rex)
Oviraptor
(Gigantoraptor)
Archaeopteryx
Modern
birds
According to the figure, what is true about modern birds?
F
Modern birds descended from Archaeopteryx.
G Modern birds share a common ancestor with T. rex.
H Modern birds share most characteristics with dinosaurs.
J
All of the above
If You Have Trouble With . . .
Question
1
2
3
4
5
6
See Lesson
27.3
27.4
27.1
27.1
25.1
26.2
TEKS
10A
10A, 3E
12A, 3A
12A
10A
7B
Animal Systems I 805