animal anatomy and physiology overview
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THE STRUCTURAL ORGANIZATION OF ANIMALS Life is characterized by a hierarchy of organization. In animals, individual cells are grouped into tissues, tissues combine to form organs, organs are organized into organ systems, and organ systems make up the entire organism. © 2013 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students often find it challenging to gain a proper understanding of the evolution of form and function relationships. Such relationships appear to have been “constructed” to meet a purpose, a consequence of deliberate planning and design. Ask students to explain why we have lungs, and they may answer something along the line of “because we need to breathe, or “because we need oxygen.” Need, however, does not cause evolution. Natural -selection involves editing rather than creating diversity. A better answer might be “Because lung-like structures conveyed an advantage in gas exchange in our ancestors.” 2. Relationships between form and function are found all around us. For some of us, noticing the connections is easy. However, many students have spent little time considering why any particular structure has its characteristic shape. Practice with examples helps to build a better understanding of these important relationships. 3. Students exploring form and function relationships should be cautioned to avoid confusing properties of an adaptation with its biological role(s). What a particular form can do, may be quite different from how it is used by an organism. For example, the long canine tooth of a saber-toothed cat might make a great letter opener, but these teeth were not used by these cats for that function (biological role)! Teaching Tips 1. When relating the principle of form and function, ask students to consider their own teeth as examples. Ask them to use their tongues to feel their teeth and relate their shape to the human diet. 2. The elastic cartilage in the human ear is a wonderful example of form and function in a tissue. Elastic fibers are abundant in the extracellular matrix, increasing the flexibility of this cartilage. Have students bend their own ears to feel the effects. 3. All muscle cells are only able to contract. None can actively relengthen. Challenge your students to explain how muscle cells return to their extended length. (Answer: Opposing muscles or other forces, such as gravity, act in opposition to relengthen muscle cells when they relax.) 4. Consider an exercise to challenge students to explore the long-term consequences of sunlight on human skin. Changes in elasticity and pigmentation of the skin might help students understand the cost of a lifetime of sun exposure. 5. Extracellular substances, such as collagen fibers, are the source of the main functional properties of many connective tissues such as tendons, ligaments, cartilage, and bone. 6. Simple squamous cells have a shape that is generally similar to a fried egg: flattened, with a bump in the middle representing the nucleus or yolk. 7. Students might enjoy this simple observation when discussing neurons. As we consider the structure and functions of neurons, we are using our own neurons to think about them. Our neurons become self-aware! 2TRANSCRIPT
Animal Anatomy and Physiology Overview
Structural Organization of Animals Exchanges with the environment
Regulating the internal environment (homeostasis) KEY
CONCEPT!Remember how cells receive nutrients from the outside
World: osmosis, diffusion, passive and active transport Even in a
multicellular organism, this holds true! Homeostasis is the control
mechanism of life THE STRUCTURAL ORGANIZATION OF ANIMALS
Life is characterized by a hierarchy of organization. In animals,
individual cells are grouped into tissues, tissues combine to form
organs, organs are organized into organ systems, and organ systems
make up the entire organism. 2013 Pearson Education, Inc. Student
Misconceptions and Concerns 1. Students often find it challenging
to gain a proper understanding of the evolution of form and
function relationships. Such relationships appear to have been
constructed to meet a purpose, a consequence of deliberate planning
and design. Ask students to explain why we have lungs, and they may
answer something along the line of because we need to breathe, or
because we need oxygen. Need, however, does not cause evolution.
Natural -selection involves editing rather than creating diversity.
A better answer might be Because lung-like structures conveyed an
advantage in gas exchange in our ancestors. 2. Relationships
between form and function are found all around us. For some of us,
noticing the connections is easy. However, many students have spent
little time considering why any particular structure has its
characteristic shape. Practice with examples helps to build a
better understanding of these important relationships. 3. Students
exploring form and function relationships should be cautioned to
avoid confusing properties of an adaptation with its biological
role(s). What a particular form can do, may be quite different from
how it is used by an organism. For example, the long canine tooth
of a saber-toothed cat might make a great letter opener, but these
teeth were not used by these cats for that function (biological
role)! Teaching Tips 1. When relating the principle of form and
function, ask students to consider their own teeth as examples. Ask
them to use their tongues to feel their teeth and relate their
shape to the human diet. 2. The elastic cartilage in the human ear
is a wonderful example of form and function in a tissue. Elastic
fibers are abundant in the extracellular matrix, increasing the
flexibility of this cartilage. Have students bend their own ears to
feel the effects. 3. All muscle cells are only able to contract.
None can actively relengthen. Challenge your students to explain
how muscle cells return to their extended length. (Answer: Opposing
muscles or other forces, such as gravity, act in opposition to
relengthen muscle cells when they relax.) 4. Consider an exercise
to challenge students to explore the long-term consequences of
sunlight on human skin. Changes in elasticity and pigmentation of
the skin might help students understand the cost of a lifetime of
sun exposure. 5. Extracellular substances, such as collagen fibers,
are the source of the main functional properties of many connective
tissues such as tendons, ligaments, cartilage, and bone. 6. Simple
squamous cells have a shape that is generally similar to a fried
egg: flattened, with a bump in the middle representing the nucleus
or yolk. 7. Students might enjoy this simple observation when
discussing neurons. As we consider the structure and functions of
neurons, we are using our own neurons to think about them. Our
neurons become self-aware! 2 Organism level: Multiple organ systems
functioning together
Figure Cellular level: Muscle cell Tissue level: Cardiac muscle
Organ level: Heart Organism level: Multiple organ systems
functioning together Organ system level: Circulatory system Figure
21.1 Structural hierarchy in a human (step 5) Form Fits Function
Analyzing a biological structure gives us clues about what it does
and how it works. 2013 Pearson Education, Inc. Student
Misconceptions and Concerns 1. Students often find it challenging
to gain a proper understanding of the evolution of form and
function relationships. Such relationships appear to have been
constructed to meet a purpose, a consequence of deliberate planning
and design. Ask students to explain why we have lungs, and they may
answer something along the line of because we need to breathe, or
because we need oxygen. Need, however, does not cause evolution.
Natural -selection involves editing rather than creating diversity.
A better answer might be Because lung-like structures conveyed an
advantage in gas exchange in our ancestors. 2. Relationships
between form and function are found all around us. For some of us,
noticing the connections is easy. However, many students have spent
little time considering why any particular structure has its
characteristic shape. Practice with examples helps to build a
better understanding of these important relationships. 3. Students
exploring form and function relationships should be cautioned to
avoid confusing properties of an adaptation with its biological
role(s). What a particular form can do, may be quite different from
how it is used by an organism. For example, the long canine tooth
of a saber-toothed cat might make a great letter opener, but these
teeth were not used by these cats for that function (biological
role)! Teaching Tips 1. When relating the principle of form and
function, ask students to consider their own teeth as examples. Ask
them to use their tongues to feel their teeth and relate their
shape to the human diet. 2. The elastic cartilage in the human ear
is a wonderful example of form and function in a tissue. Elastic
fibers are abundant in the extracellular matrix, increasing the
flexibility of this cartilage. Have students bend their own ears to
feel the effects. 3. All muscle cells are only able to contract.
None can actively relengthen. Challenge your students to explain
how muscle cells return to their extended length. (Answer: Opposing
muscles or other forces, such as gravity, act in opposition to
relengthen muscle cells when they relax.) 4. Consider an exercise
to challenge students to explore the long-term consequences of
sunlight on human skin. Changes in elasticity and pigmentation of
the skin might help students understand the cost of a lifetime of
sun exposure. 5. Extracellular substances, such as collagen fibers,
are the source of the main functional properties of many connective
tissues such as tendons, ligaments, cartilage, and bone. 6. Simple
squamous cells have a shape that is generally similar to a fried
egg: flattened, with a bump in the middle representing the nucleus
or yolk. 7. Students might enjoy this simple observation when
discussing neurons. As we consider the structure and functions of
neurons, we are using our own neurons to think about them. Our
neurons become self-aware! 4 (a) At the organism level
Figure (b) At the organ level (a) At the organism level (c) At the
cellular level Figure 21.2 Form fits function (step 3) Form Fits
Function Biologists distinguish anatomy from physiology.
Anatomy is the study of the structure of an organisms parts.
Physiology is the study of the function of those parts. 2013
Pearson Education, Inc. Student Misconceptions and Concerns 1.
Students often find it challenging to gain a proper understanding
of the evolution of form and function relationships. Such
relationships appear to have been constructed to meet a purpose, a
consequence of deliberate planning and design. Ask students to
explain why we have lungs, and they may answer something along the
line of because we need to breathe, or because we need oxygen.
Need, however, does not cause evolution. Natural -selection
involves editing rather than creating diversity. A better answer
might be Because lung-like structures conveyed an advantage in gas
exchange in our ancestors. 2. Relationships between form and
function are found all around us. For some of us, noticing the
connections is easy. However, many students have spent little time
considering why any particular structure has its characteristic
shape. Practice with examples helps to build a better understanding
of these important relationships. 3. Students exploring form and
function relationships should be cautioned to avoid confusing
properties of an adaptation with its biological role(s). What a
particular form can do, may be quite different from how it is used
by an organism. For example, the long canine tooth of a
saber-toothed cat might make a great letter opener, but these teeth
were not used by these cats for that function (biological role)!
Teaching Tips 1. When relating the principle of form and function,
ask students to consider their own teeth as examples. Ask them to
use their tongues to feel their teeth and relate their shape to the
human diet. 2. The elastic cartilage in the human ear is a
wonderful example of form and function in a tissue. Elastic fibers
are abundant in the extracellular matrix, increasing the
flexibility of this cartilage. Have students bend their own ears to
feel the effects. 3. All muscle cells are only able to contract.
None can actively relengthen. Challenge your students to explain
how muscle cells return to their extended length. (Answer: Opposing
muscles or other forces, such as gravity, act in opposition to
relengthen muscle cells when they relax.) 4. Consider an exercise
to challenge students to explore the long-term consequences of
sunlight on human skin. Changes in elasticity and pigmentation of
the skin might help students understand the cost of a lifetime of
sun exposure. 5. Extracellular substances, such as collagen fibers,
are the source of the main functional properties of many connective
tissues such as tendons, ligaments, cartilage, and bone. 6. Simple
squamous cells have a shape that is generally similar to a fried
egg: flattened, with a bump in the middle representing the nucleus
or yolk. 7. Students might enjoy this simple observation when
discussing neurons. As we consider the structure and functions of
neurons, we are using our own neurons to think about them. Our
neurons become self-aware! 6 Tissues The cell is the basic unit of
all living organisms.The only thing that is living inside of you
are your cells! In almost all animals, including humans, cells are
grouped into tissues. A tissue is an integrated group of similar
cells that performs a specific function. Animals have four main
categories of tissue. 2013 Pearson Education, Inc. Student
Misconceptions and Concerns 1. Students often find it challenging
to gain a proper understanding of the evolution of form and
function relationships. Such relationships appear to have been
constructed to meet a purpose, a consequence of deliberate planning
and design. Ask students to explain why we have lungs, and they may
answer something along the line of because we need to breathe, or
because we need oxygen. Need, however, does not cause evolution.
Natural -selection involves editing rather than creating diversity.
A better answer might be Because lung-like structures conveyed an
advantage in gas exchange in our ancestors. 2. Relationships
between form and function are found all around us. For some of us,
noticing the connections is easy. However, many students have spent
little time considering why any particular structure has its
characteristic shape. Practice with examples helps to build a
better understanding of these important relationships. 3. Students
exploring form and function relationships should be cautioned to
avoid confusing properties of an adaptation with its biological
role(s). What a particular form can do, may be quite different from
how it is used by an organism. For example, the long canine tooth
of a saber-toothed cat might make a great letter opener, but these
teeth were not used by these cats for that function (biological
role)! Teaching Tips 1. When relating the principle of form and
function, ask students to consider their own teeth as examples. Ask
them to use their tongues to feel their teeth and relate their
shape to the human diet. 2. The elastic cartilage in the human ear
is a wonderful example of form and function in a tissue. Elastic
fibers are abundant in the extracellular matrix, increasing the
flexibility of this cartilage. Have students bend their own ears to
feel the effects. 3. All muscle cells are only able to contract.
None can actively relengthen. Challenge your students to explain
how muscle cells return to their extended length. (Answer: Opposing
muscles or other forces, such as gravity, act in opposition to
relengthen muscle cells when they relax.) 4. Consider an exercise
to challenge students to explore the long-term consequences of
sunlight on human skin. Changes in elasticity and pigmentation of
the skin might help students understand the cost of a lifetime of
sun exposure. 5. Extracellular substances, such as collagen fibers,
are the source of the main functional properties of many connective
tissues such as tendons, ligaments, cartilage, and bone. 6. Simple
squamous cells have a shape that is generally similar to a fried
egg: flattened, with a bump in the middle representing the nucleus
or yolk. 7. Students might enjoy this simple observation when
discussing neurons. As we consider the structure and functions of
neurons, we are using our own neurons to think about them. Our
neurons become self-aware! 7 Epithelial tissue, also known as
epithelium,
covers the surface of the body and lines organs and cavities within
the body. Cells of epithelial tissues are fused together, form a
protective barrier, and fall off and are continuously renewed. 2013
Pearson Education, Inc. Student Misconceptions and Concerns 1.
Students often find it challenging to gain a proper understanding
of the evolution of form and function relationships. Such
relationships appear to have been constructed to meet a purpose, a
consequence of deliberate planning and design. Ask students to
explain why we have lungs, and they may answer something along the
line of because we need to breathe, or because we need oxygen.
Need, however, does not cause evolution. Natural -selection
involves editing rather than creating diversity. A better answer
might be Because lung-like structures conveyed an advantage in gas
exchange in our ancestors. 2. Relationships between form and
function are found all around us. For some of us, noticing the
connections is easy. However, many students have spent little time
considering why any particular structure has its characteristic
shape. Practice with examples helps to build a better understanding
of these important relationships. 3. Students exploring form and
function relationships should be cautioned to avoid confusing
properties of an adaptation with its biological role(s). What a
particular form can do, may be quite different from how it is used
by an organism. For example, the long canine tooth of a
saber-toothed cat might make a great letter opener, but these teeth
were not used by these cats for that function (biological role)!
Teaching Tips 1. When relating the principle of form and function,
ask students to consider their own teeth as examples. Ask them to
use their tongues to feel their teeth and relate their shape to the
human diet. 2. The elastic cartilage in the human ear is a
wonderful example of form and function in a tissue. Elastic fibers
are abundant in the extracellular matrix, increasing the
flexibility of this cartilage. Have students bend their own ears to
feel the effects. 3. All muscle cells are only able to contract.
None can actively relengthen. Challenge your students to explain
how muscle cells return to their extended length. (Answer: Opposing
muscles or other forces, such as gravity, act in opposition to
relengthen muscle cells when they relax.) 4. Consider an exercise
to challenge students to explore the long-term consequences of
sunlight on human skin. Changes in elasticity and pigmentation of
the skin might help students understand the cost of a lifetime of
sun exposure. 5. Extracellular substances, such as collagen fibers,
are the source of the main functional properties of many connective
tissues such as tendons, ligaments, cartilage, and bone. 6. Simple
squamous cells have a shape that is generally similar to a fried
egg: flattened, with a bump in the middle representing the nucleus
or yolk. 7. Students might enjoy this simple observation when
discussing neurons. As we consider the structure and functions of
neurons, we are using our own neurons to think about them. Our
neurons become self-aware! 8 Some examples of organs lined with
epithelial tissue:
Figure Some examples of organs lined with epithelial tissue: Heart
Lung Stomach Small intestine Epithelialcells Large intestine
Epithelial tissue lining esophagus Urinary bladder Epithelial
tissue lining small intestine Figure 21.3 Epithelial tissue (step
3) The structure of connective tissue is correlated with its
functions:
Connective tissues have a sparse population of cells in an
extracellular matrix consisting of a web of protein fibers within a
uniform foundation that may be liquid, jellylike, or solid. The
structure of connective tissue is correlated with its functions: to
bind and support other tissues. 2013 Pearson Education, Inc.
Student Misconceptions and Concerns 1. Students often find it
challenging to gain a proper understanding of the evolution of form
and function relationships. Such relationships appear to have been
constructed to meet a purpose, a consequence of deliberate planning
and design. Ask students to explain why we have lungs, and they may
answer something along the line of because we need to breathe, or
because we need oxygen. Need, however, does not cause evolution.
Natural -selection involves editing rather than creating diversity.
A better answer might be Because lung-like structures conveyed an
advantage in gas exchange in our ancestors. 2. Relationships
between form and function are found all around us. For some of us,
noticing the connections is easy. However, many students have spent
little time considering why any particular structure has its
characteristic shape. Practice with examples helps to build a
better understanding of these important relationships. 3. Students
exploring form and function relationships should be cautioned to
avoid confusing properties of an adaptation with its biological
role(s). What a particular form can do, may be quite different from
how it is used by an organism. For example, the long canine tooth
of a saber-toothed cat might make a great letter opener, but these
teeth were not used by these cats for that function (biological
role)! Teaching Tips 1. When relating the principle of form and
function, ask students to consider their own teeth as examples. Ask
them to use their tongues to feel their teeth and relate their
shape to the human diet. 2. The elastic cartilage in the human ear
is a wonderful example of form and function in a tissue. Elastic
fibers are abundant in the extracellular matrix, increasing the
flexibility of this cartilage. Have students bend their own ears to
feel the effects. 3. All muscle cells are only able to contract.
None can actively relengthen. Challenge your students to explain
how muscle cells return to their extended length. (Answer: Opposing
muscles or other forces, such as gravity, act in opposition to
relengthen muscle cells when they relax.) 4. Consider an exercise
to challenge students to explore the long-term consequences of
sunlight on human skin. Changes in elasticity and pigmentation of
the skin might help students understand the cost of a lifetime of
sun exposure. 5. Extracellular substances, such as collagen fibers,
are the source of the main functional properties of many connective
tissues such as tendons, ligaments, cartilage, and bone. 6. Simple
squamous cells have a shape that is generally similar to a fried
egg: flattened, with a bump in the middle representing the nucleus
or yolk. 7. Students might enjoy this simple observation when
discussing neurons. As we consider the structure and functions of
neurons, we are using our own neurons to think about them. Our
neurons become self-aware! 10 (a) Loose connective tissue (d)
Fibrous connective tissue
Figure 21.4 (a) Loose connective tissue (b) Adipose tissue (c)
Blood (d) Fibrous connective tissue (f) Bone (e) Cartilage Figure
21.4 Types of connective tissue HIERARCHICAL ORGANIZATION OF
ANIMALS
Figure 21.UN01 HIERARCHICAL ORGANIZATION OF ANIMALS Level
Description Example Cell The basic unit of all living organisms
Muscle cell Tissue A collection of similar cells performing a
specific function Cardiac muscle Organ Multiple tissues forming a
structure that performs a specific function Heart Organsystem A
team of organs that work together Circulatory system Organism A
living being, which depends on thecoordination of allstructural
levels for homeostasis and survival Person Figure 21.UN01 Summary
of Key Concepts: The Hierarchical Organization of Animals
HIERARCHICAL ORGANIZATION OF ANIMALS
Figure 21.UN01b HIERARCHICAL ORGANIZATION OF ANIMALS Level
Description Example Organsystem A team of organs that work together
Circulatory system Organism A living being, which depends on
thecoordination of allstructural levels for homeostasis and
survival Person Figure 21.UN01 Summary of Key Concepts: The
Hierarchical Organization of Animals: Organ Systems and Organisms
(part 2) Connective Tissue 14 Loose connective tissue Adipose
tissue Blood
is the most widespread connective tissue, binds epithelia to
underlying tissues, and holds organs in place. Adipose tissue
stores fat, stockpiles energy, and pads and insulates the body.
Blood is a connective tissue and contains red and white blood cells
suspended in a liquid called plasma. Fibrous connective tissue has
a dense matrix of collagen and forms tendons and ligaments. 2013
Pearson Education, Inc. Student Misconceptions and Concerns 1.
Students often find it challenging to gain a proper understanding
of the evolution of form and function relationships. Such
relationships appear to have been constructed to meet a purpose, a
consequence of deliberate planning and design. Ask students to
explain why we have lungs, and they may answer something along the
line of because we need to breathe, or because we need oxygen.
Need, however, does not cause evolution. Natural -selection
involves editing rather than creating diversity. A better answer
might be Because lung-like structures conveyed an advantage in gas
exchange in our ancestors. 2. Relationships between form and
function are found all around us. For some of us, noticing the
connections is easy. However, many students have spent little time
considering why any particular structure has its characteristic
shape. Practice with examples helps to build a better understanding
of these important relationships. 3. Students exploring form and
function relationships should be cautioned to avoid confusing
properties of an adaptation with its biological role(s). What a
particular form can do, may be quite different from how it is used
by an organism. For example, the long canine tooth of a
saber-toothed cat might make a great letter opener, but these teeth
were not used by these cats for that function (biological role)!
Teaching Tips 1. When relating the principle of form and function,
ask students to consider their own teeth as examples. Ask them to
use their tongues to feel their teeth and relate their shape to the
human diet. 2. The elastic cartilage in the human ear is a
wonderful example of form and function in a tissue. Elastic fibers
are abundant in the extracellular matrix, increasing the
flexibility of this cartilage. Have students bend their own ears to
feel the effects. 3. All muscle cells are only able to contract.
None can actively relengthen. Challenge your students to explain
how muscle cells return to their extended length. (Answer: Opposing
muscles or other forces, such as gravity, act in opposition to
relengthen muscle cells when they relax.) 4. Consider an exercise
to challenge students to explore the long-term consequences of
sunlight on human skin. Changes in elasticity and pigmentation of
the skin might help students understand the cost of a lifetime of
sun exposure. 5. Extracellular substances, such as collagen fibers,
are the source of the main functional properties of many connective
tissues such as tendons, ligaments, cartilage, and bone. 6. Simple
squamous cells have a shape that is generally similar to a fried
egg: flattened, with a bump in the middle representing the nucleus
or yolk. 7. Students might enjoy this simple observation when
discussing neurons. As we consider the structure and functions of
neurons, we are using our own neurons to think about them. Our
neurons become self-aware! 14 Connective Tissue Cartilage Bone 15
is strong but flexible,
has no blood vessels, so it heals very slowly, functions as a
flexible, boneless skeleton, and forms the shock-absorbing pads
that cushion the ends of bones including the vertebrae of the
spinal column. Bone is a rigid connective tissue and has a matrix
of collagen fibers hardened with deposits of calcium salts. 2013
Pearson Education, Inc. Student Misconceptions and Concerns 1.
Students often find it challenging to gain a proper understanding
of the evolution of form and function relationships. Such
relationships appear to have been constructed to meet a purpose, a
consequence of deliberate planning and design. Ask students to
explain why we have lungs, and they may answer something along the
line of because we need to breathe, or because we need oxygen.
Need, however, does not cause evolution. Natural -selection
involves editing rather than creating diversity. A better answer
might be Because lung-like structures conveyed an advantage in gas
exchange in our ancestors. 2. Relationships between form and
function are found all around us. For some of us, noticing the
connections is easy. However, many students have spent little time
considering why any particular structure has its characteristic
shape. Practice with examples helps to build a better understanding
of these important relationships. 3. Students exploring form and
function relationships should be cautioned to avoid confusing
properties of an adaptation with its biological role(s). What a
particular form can do, may be quite different from how it is used
by an organism. For example, the long canine tooth of a
saber-toothed cat might make a great letter opener, but these teeth
were not used by these cats for that function (biological role)!
Teaching Tips 1. When relating the principle of form and function,
ask students to consider their own teeth as examples. Ask them to
use their tongues to feel their teeth and relate their shape to the
human diet. 2. The elastic cartilage in the human ear is a
wonderful example of form and function in a tissue. Elastic fibers
are abundant in the extracellular matrix, increasing the
flexibility of this cartilage. Have students bend their own ears to
feel the effects. 3. All muscle cells are only able to contract.
None can actively relengthen. Challenge your students to explain
how muscle cells return to their extended length. (Answer: Opposing
muscles or other forces, such as gravity, act in opposition to
relengthen muscle cells when they relax.) 4. Consider an exercise
to challenge students to explore the long-term consequences of
sunlight on human skin. Changes in elasticity and pigmentation of
the skin might help students understand the cost of a lifetime of
sun exposure. 5. Extracellular substances, such as collagen fibers,
are the source of the main functional properties of many connective
tissues such as tendons, ligaments, cartilage, and bone. 6. Simple
squamous cells have a shape that is generally similar to a fried
egg: flattened, with a bump in the middle representing the nucleus
or yolk. 7. Students might enjoy this simple observation when
discussing neurons. As we consider the structure and functions of
neurons, we are using our own neurons to think about them. Our
neurons become self-aware! 15 Muscle Tissue Muscle tissue
is the most abundant tissue in most animals, consists of bundles of
long, thin, cylindrical cells called muscle fibers, and has
specialized proteins arranged into a structure that contracts when
stimulated by a signal from a nerve.contractileexcitable There are
3 types of muscle tissue: Cardiac, skeletal and smooth 2013 Pearson
Education, Inc. Student Misconceptions and Concerns 1. Students
often find it challenging to gain a proper understanding of the
evolution of form and function relationships. Such relationships
appear to have been constructed to meet a purpose, a consequence of
deliberate planning and design. Ask students to explain why we have
lungs, and they may answer something along the line of because we
need to breathe, or because we need oxygen. Need, however, does not
cause evolution. Natural -selection involves editing rather than
creating diversity. A better answer might be Because lung-like
structures conveyed an advantage in gas exchange in our ancestors.
2. Relationships between form and function are found all around us.
For some of us, noticing the connections is easy. However, many
students have spent little time considering why any particular
structure has its characteristic shape. Practice with examples
helps to build a better understanding of these important
relationships. 3. Students exploring form and function
relationships should be cautioned to avoid confusing properties of
an adaptation with its biological role(s). What a particular form
can do, may be quite different from how it is used by an organism.
For example, the long canine tooth of a saber-toothed cat might
make a great letter opener, but these teeth were not used by these
cats for that function (biological role)! Teaching Tips 1. When
relating the principle of form and function, ask students to
consider their own teeth as examples. Ask them to use their tongues
to feel their teeth and relate their shape to the human diet. 2.
The elastic cartilage in the human ear is a wonderful example of
form and function in a tissue. Elastic fibers are abundant in the
extracellular matrix, increasing the flexibility of this cartilage.
Have students bend their own ears to feel the effects. 3. All
muscle cells are only able to contract. None can actively
relengthen. Challenge your students to explain how muscle cells
return to their extended length. (Answer: Opposing muscles or other
forces, such as gravity, act in opposition to relengthen muscle
cells when they relax.) 4. Consider an exercise to challenge
students to explore the long-term consequences of sunlight on human
skin. Changes in elasticity and pigmentation of the skin might help
students understand the cost of a lifetime of sun exposure. 5.
Extracellular substances, such as collagen fibers, are the source
of the main functional properties of many connective tissues such
as tendons, ligaments, cartilage, and bone. 6. Simple squamous
cells have a shape that is generally similar to a fried egg:
flattened, with a bump in the middle representing the nucleus or
yolk. 7. Students might enjoy this simple observation when
discussing neurons. As we consider the structure and functions of
neurons, we are using our own neurons to think about them. Our
neurons become self-aware! 16 (b) Cardiac muscle (a) Skeletal
muscle (c) Smooth muscle Figure 21.5
Figure 21.5 Three types of muscle tissue HIERARCHICAL ORGANIZATION
OF ANIMALS
Figure 21.UN01a HIERARCHICAL ORGANIZATION OF ANIMALS Level
Description Example Cell The basic unit of all living organisms
Muscle cell Tissue A collection of similar cells performing a
specific function Cardiac muscle Organ Multiple tissues forming a
structure that performs a specific function Heart Figure 21.UN01
Summary of Key Concepts: The Hierarchical Organization of Animals:
Cells, Tissues and Organs (part 1) Muscle (contracts) Connective
(supports organs) Epithelial (covers
Figure 21.UN02 Muscle (contracts) Connective (supports organs)
Epithelial (covers body surfaces and organs) Nervous (relays and
integrates information) Figure 21.UN02 Summary of Key Concepts:
Tissues Muscle Tissue 20 Skeletal muscle is Cardiac muscle is
Smooth muscle is
attached to bones by tendons, responsible for voluntary movements,
and striated because the contractile proteins form a banded
pattern. Cardiac muscle is found only in heart tissue, composed of
cells that are branched and striated, involuntary, and responsible
for the contraction of the heart. Smooth muscle is named for its
lack of obvious stripes, found in the walls of various organs such
as intestines and blood vessels, and involuntary. 2013 Pearson
Education, Inc. Student Misconceptions and Concerns 1. Students
often find it challenging to gain a proper understanding of the
evolution of form and function relationships. Such relationships
appear to have been constructed to meet a purpose, a consequence of
deliberate planning and design. Ask students to explain why we have
lungs, and they may answer something along the line of because we
need to breathe, or because we need oxygen. Need, however, does not
cause evolution. Natural -selection involves editing rather than
creating diversity. A better answer might be Because lung-like
structures conveyed an advantage in gas exchange in our ancestors.
2. Relationships between form and function are found all around us.
For some of us, noticing the connections is easy. However, many
students have spent little time considering why any particular
structure has its characteristic shape. Practice with examples
helps to build a better understanding of these important
relationships. 3. Students exploring form and function
relationships should be cautioned to avoid confusing properties of
an adaptation with its biological role(s). What a particular form
can do, may be quite different from how it is used by an organism.
For example, the long canine tooth of a saber-toothed cat might
make a great letter opener, but these teeth were not used by these
cats for that function (biological role)! Teaching Tips 1. When
relating the principle of form and function, ask students to
consider their own teeth as examples. Ask them to use their tongues
to feel their teeth and relate their shape to the human diet. 2.
The elastic cartilage in the human ear is a wonderful example of
form and function in a tissue. Elastic fibers are abundant in the
extracellular matrix, increasing the flexibility of this cartilage.
Have students bend their own ears to feel the effects. 3. All
muscle cells are only able to contract. None can actively
relengthen. Challenge your students to explain how muscle cells
return to their extended length. (Answer: Opposing muscles or other
forces, such as gravity, act in opposition to relengthen muscle
cells when they relax.) 4. Consider an exercise to challenge
students to explore the long-term consequences of sunlight on human
skin. Changes in elasticity and pigmentation of the skin might help
students understand the cost of a lifetime of sun exposure. 5.
Extracellular substances, such as collagen fibers, are the source
of the main functional properties of many connective tissues such
as tendons, ligaments, cartilage, and bone. 6. Simple squamous
cells have a shape that is generally similar to a fried egg:
flattened, with a bump in the middle representing the nucleus or
yolk. 7. Students might enjoy this simple observation when
discussing neurons. As we consider the structure and functions of
neurons, we are using our own neurons to think about them. Our
neurons become self-aware! 20 The basic unit of nervous tissue is
the neuron, or nerve cell.
makes communication of sensory information possible, is found in
your brain and spinal cord, and consists of a network of neurons.
The basic unit of nervous tissue is the neuron, or nerve cell. 2013
Pearson Education, Inc. Student Misconceptions and Concerns 1.
Students often find it challenging to gain a proper understanding
of the evolution of form and function relationships. Such
relationships appear to have been constructed to meet a purpose, a
consequence of deliberate planning and design. Ask students to
explain why we have lungs, and they may answer something along the
line of because we need to breathe, or because we need oxygen.
Need, however, does not cause evolution. Natural -selection
involves editing rather than creating diversity. A better answer
might be Because lung-like structures conveyed an advantage in gas
exchange in our ancestors. 2. Relationships between form and
function are found all around us. For some of us, noticing the
connections is easy. However, many students have spent little time
considering why any particular structure has its characteristic
shape. Practice with examples helps to build a better understanding
of these important relationships. 3. Students exploring form and
function relationships should be cautioned to avoid confusing
properties of an adaptation with its biological role(s). What a
particular form can do, may be quite different from how it is used
by an organism. For example, the long canine tooth of a
saber-toothed cat might make a great letter opener, but these teeth
were not used by these cats for that function (biological role)!
Teaching Tips 1. When relating the principle of form and function,
ask students to consider their own teeth as examples. Ask them to
use their tongues to feel their teeth and relate their shape to the
human diet. 2. The elastic cartilage in the human ear is a
wonderful example of form and function in a tissue. Elastic fibers
are abundant in the extracellular matrix, increasing the
flexibility of this cartilage. Have students bend their own ears to
feel the effects. 3. All muscle cells are only able to contract.
None can actively relengthen. Challenge your students to explain
how muscle cells return to their extended length. (Answer: Opposing
muscles or other forces, such as gravity, act in opposition to
relengthen muscle cells when they relax.) 4. Consider an exercise
to challenge students to explore the long-term consequences of
sunlight on human skin. Changes in elasticity and pigmentation of
the skin might help students understand the cost of a lifetime of
sun exposure. 5. Extracellular substances, such as collagen fibers,
are the source of the main functional properties of many connective
tissues such as tendons, ligaments, cartilage, and bone. 6. Simple
squamous cells have a shape that is generally similar to a fried
egg: flattened, with a bump in the middle representing the nucleus
or yolk. 7. Students might enjoy this simple observation when
discussing neurons. As we consider the structure and functions of
neurons, we are using our own neurons to think about them. Our
neurons become self-aware! 21 Brain Spinal cord Signal-receiving
extensions Cell body Nerve Signal-
Figure 21.6 Brain Spinal cord Signal-receiving extensions Cell body
Nerve Signal- transmitting extension LM Figure 21.6 Nervous tissue
Organs and Organ Systems
An organ consists of two or more tissues packaged into one working
unit that performs a specific function. Examples include the heart,
liver, stomach, brain, and small intestines. 2013 Pearson
Education, Inc. Student Misconceptions and Concerns 1. Students
often find it challenging to gain a proper understanding of the
evolution of form and function relationships. Such relationships
appear to have been constructed to meet a purpose, a consequence of
deliberate planning and design. Ask students to explain why we have
lungs, and they may answer something along the line of because we
need to breathe, or because we need oxygen. Need, however, does not
cause evolution. Natural -selection involves editing rather than
creating diversity. A better answer might be Because lung-like
structures conveyed an advantage in gas exchange in our ancestors.
2. Relationships between form and function are found all around us.
For some of us, noticing the connections is easy. However, many
students have spent little time considering why any particular
structure has its characteristic shape. Practice with examples
helps to build a better understanding of these important
relationships. 3. Students exploring form and function
relationships should be cautioned to avoid confusing properties of
an adaptation with its biological role(s). What a particular form
can do, may be quite different from how it is used by an organism.
For example, the long canine tooth of a saber-toothed cat might
make a great letter opener, but these teeth were not used by these
cats for that function (biological role)! Teaching Tips 1. When
relating the principle of form and function, ask students to
consider their own teeth as examples. Ask them to use their tongues
to feel their teeth and relate their shape to the human diet. 2.
The elastic cartilage in the human ear is a wonderful example of
form and function in a tissue. Elastic fibers are abundant in the
extracellular matrix, increasing the flexibility of this cartilage.
Have students bend their own ears to feel the effects. 3. All
muscle cells are only able to contract. None can actively
relengthen. Challenge your students to explain how muscle cells
return to their extended length. (Answer: Opposing muscles or other
forces, such as gravity, act in opposition to relengthen muscle
cells when they relax.) 4. Consider an exercise to challenge
students to explore the long-term consequences of sunlight on human
skin. Changes in elasticity and pigmentation of the skin might help
students understand the cost of a lifetime of sun exposure. 5.
Extracellular substances, such as collagen fibers, are the source
of the main functional properties of many connective tissues such
as tendons, ligaments, cartilage, and bone. 6. Simple squamous
cells have a shape that is generally similar to a fried egg:
flattened, with a bump in the middle representing the nucleus or
yolk. 7. Students might enjoy this simple observation when
discussing neurons. As we consider the structure and functions of
neurons, we are using our own neurons to think about them. Our
neurons become self-aware! 23 Small intestine (cut open) Epithelial
tissue Connective tissue
Figure 21.7 Small intestine (cut open) Epithelial tissue Connective
tissue (containing blood and lymph vessels) Smooth muscle tissue
(two layers) Epithelial tissue Connective tissue Figure 21.7 Tissue
layers of the small intestine, an organ Organs and Organ
Systems
Organ systems are teams of organs that work together and perform
vital body functions.There are 11 organ systems in higher organisms
Skeletal Circulatory Respiratory Muscular Digestive Urinary
Endocrine Reproductive Integumentary Lymphatic Nervous 2013 Pearson
Education, Inc. Student Misconceptions and Concerns 1. Students
often find it challenging to gain a proper understanding of the
evolution of form and function relationships. Such relationships
appear to have been constructed to meet a purpose, a consequence of
deliberate planning and design. Ask students to explain why we have
lungs, and they may answer something along the line of because we
need to breathe, or because we need oxygen. Need, however, does not
cause evolution. Natural -selection involves editing rather than
creating diversity. A better answer might be Because lung-like
structures conveyed an advantage in gas exchange in our ancestors.
2. Relationships between form and function are found all around us.
For some of us, noticing the connections is easy. However, many
students have spent little time considering why any particular
structure has its characteristic shape. Practice with examples
helps to build a better understanding of these important
relationships. 3. Students exploring form and function
relationships should be cautioned to avoid confusing properties of
an adaptation with its biological role(s). What a particular form
can do, may be quite different from how it is used by an organism.
For example, the long canine tooth of a saber-toothed cat might
make a great letter opener, but these teeth were not used by these
cats for that function (biological role)! Teaching Tips 1. When
relating the principle of form and function, ask students to
consider their own teeth as examples. Ask them to use their tongues
to feel their teeth and relate their shape to the human diet. 2.
The elastic cartilage in the human ear is a wonderful example of
form and function in a tissue. Elastic fibers are abundant in the
extracellular matrix, increasing the flexibility of this cartilage.
Have students bend their own ears to feel the effects. 3. All
muscle cells are only able to contract. None can actively
relengthen. Challenge your students to explain how muscle cells
return to their extended length. (Answer: Opposing muscles or other
forces, such as gravity, act in opposition to relengthen muscle
cells when they relax.) 4. Consider an exercise to challenge
students to explore the long-term consequences of sunlight on human
skin. Changes in elasticity and pigmentation of the skin might help
students understand the cost of a lifetime of sun exposure. 5.
Extracellular substances, such as collagen fibers, are the source
of the main functional properties of many connective tissues such
as tendons, ligaments, cartilage, and bone. 6. Simple squamous
cells have a shape that is generally similar to a fried egg:
flattened, with a bump in the middle representing the nucleus or
yolk. 7. Students might enjoy this simple observation when
discussing neurons. As we consider the structure and functions of
neurons, we are using our own neurons to think about them. Our
neurons become self-aware! 25 It also plays a role in Ca Metabolism
and maintainace Of pH Bone
Figure 21.8a Skeletal system: supports body and anchors muscles It
also plays a role in Ca Metabolism and maintainace Of pH Bone
Cartilage Figure 21.8 Organ systems of a vertebrate: skeletal (part
1) transports substances throughout body
Figure 21.8b Circulatory system: transports substances throughout
body Heart Blood vessels Figure 21.8 Organ systems of a vertebrate:
circulatory (part 2) Respiratory system: exchanges O2 and CO2
between blood and air
Figure 21.8c Respiratory system: exchanges O2 and CO2 between blood
and air And helps to maintain pH Nasal cavity Pharynx Larynx
Trachea Bronchus Lung Figure 21.8 Organ systems of a vertebrate:
respiratory (part 3) And is the heating system of the body
Figure 21.8d Muscular system: moves the body And is the heating
system of the body Skeletal muscles Figure 21.8 Organ systems of a
vertebrate: muscular (part 4) Digestive system: breaks down food
and absorbs nutrients Mouth
Figure 21.8e Digestive system: breaks down food and absorbs
nutrients Mouth Esophagus Liver Stomach Large intestine Small
intestine Anus Figure 21.8 Organ systems of a vertebrate: digestive
(part 5) Urinary system: rids body of certain wastes Kidneys are
responsible
Figure 21.8f Urinary system: rids body of certain wastes Kidneys
are responsible For monitoring BP and # of RBCs Kidney
Urinarybladder Ureter Urethra Figure 21.8 Organ systems of a
vertebrate: urinary (part 6) Endocrine system: secretes hormones
that regulate body Hypothalamus
Figure 21.8g Endocrine system: secretes hormones that regulate body
Hypothalamus Pituitary gland Parathyroid gland Thyroid gland
Adrenal gland Ovary (female) Pancreas Testis (male) Figure 21.8
Organ systems of a vertebrate: endocrine (part 7) Reproductive
system: produces gametes and offspring Responsible for
Figure 21.8h Reproductive system: produces gametes and offspring
Responsible for Homeostasis of the Species! Seminal vesicles
Prostate gland Oviduct Vas deferens Ovary Penis Uterus Urethra
Vagina Testis Figure 21.8 Organ systems of a vertebrate:
reproductive (part 8) system: protects body and is The first line
of defense from Pathogens
Figure 21.8i Integumentary system: protects body and is The first
line of defense from Pathogens It is connected to the nervous
System and is responsible for Transmitting information about The
outside world to the brain Hair Skin Nail Figure 21.8 Organ systems
of a vertebrate: integumentary (part 9) Lymphatic and immune
system: defends against disease Thymus Spleen
Figure 21.8j Lymphatic and immune system: defends against disease
Thymus Spleen Lymph nodes Lymphatic vessels Figure 21.8 Organ
systems of a vertebrate: lymphatic and immune (part 10) Nervous
system: processes sensory Brain information and controls
Figure 21.8k Nervous system: processes sensory information and
controls Responses (motor) Brain Sense organ (ear) Spinal cord
Nerves Figure 21.8 Organ systems of a vertebrate: nervous (part 11)
EXCHANGES WITH THE EXTERNAL ENVIRONMENT
Every organism is an open system, continuously exchanging chemicals
and energy with its surroundings to survive. An animals size and
shape affect its exchanges with its surrounding environment. All
living cells must be bathed in a watery solution so that exchange
of materials can occur. 2013 Pearson Education, Inc. Student
Misconceptions and Concerns 1. It can be difficult for students to
think of their own bodies in such simple terms as surfaces and
tubes. Perceiving the digestive tract as one continuous tube, in
which food that passes through never technically enters the body,
is one such challenge. Illustrate these fundamental principles
first using simple animals as examples. Then apply these principles
to humans as a final test of comprehension. 2. If students have not
previously examined the diversity of animals, consider a brief
overview of the fundamental body plans before explaining how these
fundamental principles of form and function generally apply to the
animal kingdom. Teaching Tips 1. Students often fail to consider
the overall significance of body size. Consider asking your
students to think about the impact of being small. Do they recall
ever having trouble emerging from a swimming pool because of the
adhesive properties of water? Yet, small insects that land on a
ponds surface may find these forces to be lethal, preventing these
organisms from breaking away from the waters surface! In addition,
are your students frequently prevented from leaving their homes
because of high winds, simply unable to walk around outside? The
movements of small insects are often prevented by winds that would
do little more than toss around our hair! Many campers know that
mosquitoes and flies are less of a pest on days when there is a
good breeze. 2. The consequences of large size in organisms require
transport and exchange systems extending to the deepest inner
regions. Whether we think of a whale, a giant redwood, or the
United States, these principles apply. By analogy, the railway and
highway systems of the United States transport essential products
from ocean ports to the deepest interior regions, where warehouses
and other transport systems deliver the goods to stores for
purchase. A person living near the ocean may obtain food directly,
by fishing in the ocean. A person living in the Midwest may
purchase ocean fish at a store or at a restaurant! 3. Organisms and
individual cells need sufficient surface exchange and transport
systems to support their surface-to-volume ratios. Cell size is
limited, in part, by the ability of a cell to exchange materials
efficiently with its surface. Thus, adaptations that increase
surface area can permit cells to reach larger sizes. 4. You might
note how sponges are well adapted to maximize their surface area
exposed to water. Their highly porous system dramatically increases
the region engaged in water filtration. 5. The stratified squamous
epithelium on most outside surfaces of our body resists abrasions
in part because it is keratinized. However, the nonkeratinized
epithelial tissues that line our body cavities, such as the mouth,
pharynx, esophagus, and anus, are also resistant to abrasion as a
result ofmucus coatings, which provide friction-reducing
lubrication.Students may not realize that the same type of tissue
performs similar functions in very different parts of the body.
EXCHANGES WITH THE EXTERNAL ENVIRONMENT
The entire surface area of a single-celled amoeba is in contact
with its watery environment. A hydra has a body wall only two cell
layers thick. Both layers of cells are bathed in pond water,
enabling exchange with the environment. 2013 Pearson Education,
Inc. Student Misconceptions and Concerns 1. It can be difficult for
students to think of their own bodies in such simple terms as
surfaces and tubes. Perceiving the digestive tract as one
continuous tube, in which food that passes through never
technically enters the body, is one such challenge. Illustrate
these fundamental principles first using simple animals as
examples. Then apply these principles to humans as a final test of
comprehension. 2. If students have not previously examined the
diversity of animals, consider a brief overview of the fundamental
body plans before explaining how these fundamental principles of
form and function generally apply to the animal kingdom. Teaching
Tips 1. Students often fail to consider the overall significance of
body size. Consider asking your students to think about the impact
of being small. Do they recall ever having trouble emerging from a
swimming pool because of the adhesive properties of water? Yet,
small insects that land on a ponds surface may find these forces to
be lethal, preventing these organisms from breaking away from the
waters surface! In addition, are your students frequently prevented
from leaving their homes because of high winds, simply unable to
walk around outside? The movements of small insects are often
prevented by winds that would do little more than toss around our
hair! Many campers know that mosquitoes and flies are less of a
pest on days when there is a good breeze. 2. The consequences of
large size in organisms require transport and exchange systems
extending to the deepest inner regions. Whether we think of a
whale, a giant redwood, or the United States, these principles
apply. By analogy, the railway and highway systems of the United
States transport essential products from ocean ports to the deepest
interior regions, where warehouses and other transport systems
deliver the goods to stores for purchase. A person living near the
ocean may obtain food directly, by fishing in the ocean. A person
living in the Midwest may purchase ocean fish at a store or at a
restaurant! 3. Organisms and individual cells need sufficient
surface exchange and transport systems to support their
surface-to-volume ratios. Cell size is limited, in part, by the
ability of a cell to exchange materials efficiently with its
surface. Thus, adaptations that increase surface area can permit
cells to reach larger sizes. 4. You might note how sponges are well
adapted to maximize their surface area exposed to water. Their
highly porous system dramatically increases the region engaged in
water filtration. 5. The stratified squamous epithelium on most
outside surfaces of our body resists abrasions in part because it
is keratinized. However, the nonkeratinized epithelial tissues that
line our body cavities, such as the mouth, pharynx, esophagus, and
anus, are also resistant to abrasion as a result ofmucus coatings,
which provide friction-reducing lubrication.Students may not
realize that the same type of tissue performs similar functions in
very different parts of the body. 38 (a) Single cell (b) Two cell
layers Mouth Gastrovascular cavity
Figure 21.9 Mouth Gastrovascular cavity Exchange Exchange Exchange
(a) Single cell (b) Two cell layers Figure 21.9 Contact of simple
organisms with the environment EXCHANGES WITH THE EXTERNAL
ENVIRONMENT
Animals with complex body forms face the same basic problems. Every
cell must be bathed in fluid and have access to resources from the
outside environment. 2013 Pearson Education, Inc. Student
Misconceptions and Concerns 1. It can be difficult for students to
think of their own bodies in such simple terms as surfaces and
tubes. Perceiving the digestive tract as one continuous tube, in
which food that passes through never technically enters the body,
is one such challenge. Illustrate these fundamental principles
first using simple animals as examples. Then apply these principles
to humans as a final test of comprehension. 2. If students have not
previously examined the diversity of animals, consider a brief
overview of the fundamental body plans before explaining how these
fundamental principles of form and function generally apply to the
animal kingdom. Teaching Tips 1. Students often fail to consider
the overall significance of body size. Consider asking your
students to think about the impact of being small. Do they recall
ever having trouble emerging from a swimming pool because of the
adhesive properties of water? Yet, small insects that land on a
ponds surface may find these forces to be lethal, preventing these
organisms from breaking away from the waters surface! In addition,
are your students frequently prevented from leaving their homes
because of high winds, simply unable to walk around outside? The
movements of small insects are often prevented by winds that would
do little more than toss around our hair! Many campers know that
mosquitoes and flies are less of a pest on days when there is a
good breeze. 2. The consequences of large size in organisms require
transport and exchange systems extending to the deepest inner
regions. Whether we think of a whale, a giant redwood, or the
United States, these principles apply. By analogy, the railway and
highway systems of the United States transport essential products
from ocean ports to the deepest interior regions, where warehouses
and other transport systems deliver the goods to stores for
purchase. A person living near the ocean may obtain food directly,
by fishing in the ocean. A person living in the Midwest may
purchase ocean fish at a store or at a restaurant! 3. Organisms and
individual cells need sufficient surface exchange and transport
systems to support their surface-to-volume ratios. Cell size is
limited, in part, by the ability of a cell to exchange materials
efficiently with its surface. Thus, adaptations that increase
surface area can permit cells to reach larger sizes. 4. You might
note how sponges are well adapted to maximize their surface area
exposed to water. Their highly porous system dramatically increases
the region engaged in water filtration. 5. The stratified squamous
epithelium on most outside surfaces of our body resists abrasions
in part because it is keratinized. However, the nonkeratinized
epithelial tissues that line our body cavities, such as the mouth,
pharynx, esophagus, and anus, are also resistant to abrasion as a
result ofmucus coatings, which provide friction-reducing
lubrication.Students may not realize that the same type of tissue
performs similar functions in very different parts of the body. 40
EXCHANGES WITH THE EXTERNAL ENVIRONMENT
Complex animals have evolved extensively folded or branched
internal surfaces that maximize surface area for exchange with the
immediate environment. Lungs have a very large total surface area
and exchange oxygen and carbon dioxide with the air you breathe.
2013 Pearson Education, Inc. Student Misconceptions and Concerns 1.
It can be difficult for students to think of their own bodies in
such simple terms as surfaces and tubes. Perceiving the digestive
tract as one continuous tube, in which food that passes through
never technically enters the body, is one such challenge.
Illustrate these fundamental principles first using simple animals
as examples. Then apply these principles to humans as a final test
of comprehension. 2. If students have not previously examined the
diversity of animals, consider a brief overview of the fundamental
body plans before explaining how these fundamental principles of
form and function generally apply to the animal kingdom. Teaching
Tips 1. Students often fail to consider the overall significance of
body size. Consider asking your students to think about the impact
of being small. Do they recall ever having trouble emerging from a
swimming pool because of the adhesive properties of water? Yet,
small insects that land on a ponds surface may find these forces to
be lethal, preventing these organisms from breaking away from the
waters surface! In addition, are your students frequently prevented
from leaving their homes because of high winds, simply unable to
walk around outside? The movements of small insects are often
prevented by winds that would do little more than toss around our
hair! Many campers know that mosquitoes and flies are less of a
pest on days when there is a good breeze. 2. The consequences of
large size in organisms require transport and exchange systems
extending to the deepest inner regions. Whether we think of a
whale, a giant redwood, or the United States, these principles
apply. By analogy, the railway and highway systems of the United
States transport essential products from ocean ports to the deepest
interior regions, where warehouses and other transport systems
deliver the goods to stores for purchase. A person living near the
ocean may obtain food directly, by fishing in the ocean. A person
living in the Midwest may purchase ocean fish at a store or at a
restaurant! 3. Organisms and individual cells need sufficient
surface exchange and transport systems to support their
surface-to-volume ratios. Cell size is limited, in part, by the
ability of a cell to exchange materials efficiently with its
surface. Thus, adaptations that increase surface area can permit
cells to reach larger sizes. 4. You might note how sponges are well
adapted to maximize their surface area exposed to water. Their
highly porous system dramatically increases the region engaged in
water filtration. 5. The stratified squamous epithelium on most
outside surfaces of our body resists abrasions in part because it
is keratinized. However, the nonkeratinized epithelial tissues that
line our body cavities, such as the mouth, pharynx, esophagus, and
anus, are also resistant to abrasion as a result ofmucus coatings,
which provide friction-reducing lubrication.Students may not
realize that the same type of tissue performs similar functions in
very different parts of the body. 41 Figure 21.10 Figure The
branched surface area of the human lung EXCHANGES WITH THE EXTERNAL
ENVIRONMENT
Animals use three organ systems to exchange materials with the
external environment: digestive, respiratory, and urinary. 2013
Pearson Education, Inc. Student Misconceptions and Concerns 1. It
can be difficult for students to think of their own bodies in such
simple terms as surfaces and tubes. Perceiving the digestive tract
as one continuous tube, in which food that passes through never
technically enters the body, is one such challenge. Illustrate
these fundamental principles first using simple animals as
examples. Then apply these principles to humans as a final test of
comprehension. 2. If students have not previously examined the
diversity of animals, consider a brief overview of the fundamental
body plans before explaining how these fundamental principles of
form and function generally apply to the animal kingdom. Teaching
Tips 1. Students often fail to consider the overall significance of
body size. Consider asking your students to think about the impact
of being small. Do they recall ever having trouble emerging from a
swimming pool because of the adhesive properties of water? Yet,
small insects that land on a ponds surface may find these forces to
be lethal, preventing these organisms from breaking away from the
waters surface! In addition, are your students frequently prevented
from leaving their homes because of high winds, simply unable to
walk around outside? The movements of small insects are often
prevented by winds that would do little more than toss around our
hair! Many campers know that mosquitoes and flies are less of a
pest on days when there is a good breeze. 2. The consequences of
large size in organisms require transport and exchange systems
extending to the deepest inner regions. Whether we think of a
whale, a giant redwood, or the United States, these principles
apply. By analogy, the railway and highway systems of the United
States transport essential products from ocean ports to the deepest
interior regions, where warehouses and other transport systems
deliver the goods to stores for purchase. A person living near the
ocean may obtain food directly, by fishing in the ocean. A person
living in the Midwest may purchase ocean fish at a store or at a
restaurant! 3. Organisms and individual cells need sufficient
surface exchange and transport systems to support their
surface-to-volume ratios. Cell size is limited, in part, by the
ability of a cell to exchange materials efficiently with its
surface. Thus, adaptations that increase surface area can permit
cells to reach larger sizes. 4. You might note how sponges are well
adapted to maximize their surface area exposed to water. Their
highly porous system dramatically increases the region engaged in
water filtration. 5. The stratified squamous epithelium on most
outside surfaces of our body resists abrasions in part because it
is keratinized. However, the nonkeratinized epithelial tissues that
line our body cavities, such as the mouth, pharynx, esophagus, and
anus, are also resistant to abrasion as a result ofmucus coatings,
which provide friction-reducing lubrication.Students may not
realize that the same type of tissue performs similar functions in
very different parts of the body. 43 EXCHANGES WITH THE EXTERNAL
ENVIRONMENT
The circulatory system connects to nearly every organ system,
transports needed materials from the environment to the bodys
tissues, and carries waste away. 2013 Pearson Education, Inc.
Student Misconceptions and Concerns 1. It can be difficult for
students to think of their own bodies in such simple terms as
surfaces and tubes. Perceiving the digestive tract as one
continuous tube, in which food that passes through never
technically enters the body, is one such challenge. Illustrate
these fundamental principles first using simple animals as
examples. Then apply these principles to humans as a final test of
comprehension. 2. If students have not previously examined the
diversity of animals, consider a brief overview of the fundamental
body plans before explaining how these fundamental principles of
form and function generally apply to the animal kingdom. Teaching
Tips 1. Students often fail to consider the overall significance of
body size. Consider asking your students to think about the impact
of being small. Do they recall ever having trouble emerging from a
swimming pool because of the adhesive properties of water? Yet,
small insects that land on a ponds surface may find these forces to
be lethal, preventing these organisms from breaking away from the
waters surface! In addition, are your students frequently prevented
from leaving their homes because of high winds, simply unable to
walk around outside? The movements of small insects are often
prevented by winds that would do little more than toss around our
hair! Many campers know that mosquitoes and flies are less of a
pest on days when there is a good breeze. 2. The consequences of
large size in organisms require transport and exchange systems
extending to the deepest inner regions. Whether we think of a
whale, a giant redwood, or the United States, these principles
apply. By analogy, the railway and highway systems of the United
States transport essential products from ocean ports to the deepest
interior regions, where warehouses and other transport systems
deliver the goods to stores for purchase. A person living near the
ocean may obtain food directly, by fishing in the ocean. A person
living in the Midwest may purchase ocean fish at a store or at a
restaurant! 3. Organisms and individual cells need sufficient
surface exchange and transport systems to support their
surface-to-volume ratios. Cell size is limited, in part, by the
ability of a cell to exchange materials efficiently with its
surface. Thus, adaptations that increase surface area can permit
cells to reach larger sizes. 4. You might note how sponges are well
adapted to maximize their surface area exposed to water. Their
highly porous system dramatically increases the region engaged in
water filtration. 5. The stratified squamous epithelium on most
outside surfaces of our body resists abrasions in part because it
is keratinized. However, the nonkeratinized epithelial tissues that
line our body cavities, such as the mouth, pharynx, esophagus, and
anus, are also resistant to abrasion as a result ofmucus coatings,
which provide friction-reducing lubrication.Students may not
realize that the same type of tissue performs similar functions in
very different parts of the body. 44 Unabsorbed matter (feces)
Metabolic waste products (such as urine)
Figure 21.11 External environment CO2 Mouth Food O2 Animal
Respiratory system Digestive system Blood Interstitial fluid Heart
Nutrients Circulatory system Body cells Urinary system Anus
Unabsorbed matter (feces) Metabolic waste products(such as urine)
Figure Exchange between the external environment and the internal
environment of complex animals REGULATING THE INTERNAL
ENVIRONMENT
Animals adjust to a changing environment. 2013 Pearson Education,
Inc. Student Misconceptions and Concerns 1. The concept of
homeostasis may be new to many students, who have never considered
how organisms maintain their structure and physiology. Analogies to
other systems that engage in self-regulation (noted in the text and
below) can help. 2. The kidneys role in filtration and selective
reabsorption may initially be confusing to many students. The
process is a bit like cleaning up a closet by removing all the
contents and then selectively refilling the closet with what you
wish to store. Teaching Tips 1. Challenge your students to think of
other examples of negative and positive feedback. Students from
diverse disciplines may think of many new examples, including
mechanisms in an automobile. 2. The terms warm-blooded and
cold-blooded are less precise than endotherm and ectotherm.
Encourage students to discuss why endotherm and ectotherm are
preferred. 3. Ask your students to explain the adaptive advantages
of endothermy and ectothermy. You might prompt the discussion by
noting that endotherms consume about 10 times as many calories as
ectotherms of equivalent body mass. What might be the advantages
worth this additional cost for endotherms? 4. Heat generation
resulting from aerobic metabolism is analogous to heat generation
in the engine of an automobile. In both cases, the heat is a
by-product of the process. In the winter, this excess heat helps
keep the body and an automobile warm. In the summer, both the body
and the automobiles engine must work to keep from overheating. 5.
Have students list the many factors that affect heat gain and loss
during times of physical activity. These include (a) the age of the
personyounger people tend to have higher metabolic rates, (b) the
level of physical activityaerobic metabolism increases to generate
ATP to move muscles, (c) proper hydration to permit adequate
sweating, (d) the color of the persons clothing, (e) the intensity
of sunlight, (f) higher humidity levelswhich decrease evaporative
cooling, (g) intensity of windwhich promotes evaporative cooling,
and (h) the physical condition of the person. 6. Ask students to
explain how blood vessel constriction at the body surface,
shivering, and a general increase in metabolism help a person to
keep warm in a cold environment. 7. Tylenol (acetaminophen) is
often used to reduce fevers. Discuss with your students the
advantages and disadvantages of using drugs to lower a fever. 8.
Students might better understand the problems faced by freshwater
fish if you relate it to what occurs when they soak their hands in
water. Students will likely recall that their skin wrinkles when
soaked in water. Some may have noticed that their hands wrinkle
even faster in soapy water. Skin absorbs water by osmosis (just as
a freshwater fish gains water). Oils on our skin reduce the influx
of water. Thus soapy water, which washes away these oils, speeds up
the process. The wrinkling occurs because the skin can expand only
in certain areas, creating puckers. 9. A moderately full human
urinary bladder holds about 500 ml (or 1 pint) of fluid. The
maximum capacity of the bladder may reach double that volume,
although when overdistended, it can burst! 10. The unfortunate
shortage of kidneys and other organs available for transplant is a
major health issue. Consider sharing this issue with your class.
Many state and federal organ donation organizations can be located
by a quick Internet search. The National Kidney Foundation site
(www.kidney.org/) includes information on kidney donation. 46
Homeostasis Homeostasis is the bodys ability to stay relatively
unchanged even when the world around it changes. The internal
environment of vertebrates includes the interstitial fluid that
fills the spaces between cells and exchanges nutrients and wastes
with microscopic blood vessels. 2013 Pearson Education, Inc.
Student Misconceptions and Concerns 1. The concept of homeostasis
may be new to many students, who have never considered how
organisms maintain their structure and physiology. Analogies to
other systems that engage in self-regulation (noted in the text and
below) can help. 2. The kidneys role in filtration and selective
reabsorption may initially be confusing to many students. The
process is a bit like cleaning up a closet by removing all the
contents and then selectively refilling the closet with what you
wish to store. Teaching Tips 1. Challenge your students to think of
other examples of negative and positive feedback. Students from
diverse disciplines may think of many new examples, including
mechanisms in an automobile. 2. The terms warm-blooded and
cold-blooded are less precise than endotherm and ectotherm.
Encourage students to discuss why endotherm and ectotherm are
preferred. 3. Ask your students to explain the adaptive advantages
of endothermy and ectothermy. You might prompt the discussion by
noting that endotherms consume about 10 times as many calories as
ectotherms of equivalent body mass. What might be the advantages
worth this additional cost for endotherms? 4. Heat generation
resulting from aerobic metabolism is analogous to heat generation
in the engine of an automobile. In both cases, the heat is a
by-product of the process. In the winter, this excess heat helps
keep the body and an automobile warm. In the summer, both the body
and the automobiles engine must work to keep from overheating. 5.
Have students list the many factors that affect heat gain and loss
during times of physical activity. These include (a) the age of the
personyounger people tend to have higher metabolic rates, (b) the
level of physical activityaerobic metabolism increases to generate
ATP to move muscles, (c) proper hydration to permit adequate
sweating, (d) the color of the persons clothing, (e) the intensity
of sunlight, (f) higher humidity levelswhich decrease evaporative
cooling, (g) intensity of windwhich promotes evaporative cooling,
and (h) the physical condition of the person. 6. Ask students to
explain how blood vessel constriction at the body surface,
shivering, and a general increase in metabolism help a person to
keep warm in a cold environment. 7. Tylenol (acetaminophen) is
often used to reduce fevers. Discuss with your students the
advantages and disadvantages of using drugs to lower a fever. 8.
Students might better understand the problems faced by freshwater
fish if you relate it to what occurs when they soak their hands in
water. Students will likely recall that their skin wrinkles when
soaked in water. Some may have noticed that their hands wrinkle
even faster in soapy water. Skin absorbs water by osmosis (just as
a freshwater fish gains water). Oils on our skin reduce the influx
of water. Thus soapy water, which washes away these oils, speeds up
the process. The wrinkling occurs because the skin can expand only
in certain areas, creating puckers. 9. A moderately full human
urinary bladder holds about 500 ml (or 1 pint) of fluid. The
maximum capacity of the bladder may reach double that volume,
although when overdistended, it can burst! 10. The unfortunate
shortage of kidneys and other organs available for transplant is a
major health issue. Consider sharing this issue with your class.
Many state and federal organ donation organizations can be located
by a quick Internet search. The National Kidney Foundation site
(www.kidney.org/) includes information on kidney donation. 47
HOMEOSTATIC MECHANISMS
Figure 21.12 External environment Animals internal environment
HOMEOSTATIC MECHANISMS Large external changes Small internal
changes Figure Homeostasis Negative and Positive Feedback
Most mechanisms of homeostasis depend on a principle called
negative feedback, in which the results of a process inhibit that
same process, such as a thermostat that turns off a heater when
room temperature rises to the set point. 2013 Pearson Education,
Inc. Student Misconceptions and Concerns 1. The concept of
homeostasis may be new to many students, who have never considered
how organisms maintain their structure and physiology. Analogies to
other systems that engage in self-regulation (noted in the text and
below) can help. 2. The kidneys role in filtration and selective
reabsorption may initially be confusing to many students. The
process is a bit like cleaning up a closet by removing all the
contents and then selectively refilling the closet with what you
wish to store. Teaching Tips 1. Challenge your students to think of
other examples of negative and positive feedback. Students from
diverse disciplines may think of many new examples, including
mechanisms in an automobile. 2. The terms warm-blooded and
cold-blooded are less precise than endotherm and ectotherm.
Encourage students to discuss why endotherm and ectotherm are
preferred. 3. Ask your students to explain the adaptive advantages
of endothermy and ectothermy. You might prompt the discussion by
noting that endotherms consume about 10 times as many calories as
ectotherms of equivalent body mass. What might be the advantages
worth this additional cost for endotherms? 4. Heat generation
resulting from aerobic metabolism is analogous to heat generation
in the engine of an automobile. In both cases, the heat is a
by-product of the process. In the winter, this excess heat helps
keep the body and an automobile warm. In the summer, both the body
and the automobiles engine must work to keep from overheating. 5.
Have students list the many factors that affect heat gain and loss
during times of physical activity. These include (a) the age of the
personyounger people tend to have higher metabolic rates, (b) the
level of physical activityaerobic metabolism increases to generate
ATP to move muscles, (c) proper hydration to permit adequate
sweating, (d) the color of the persons clothing, (e) the intensity
of sunlight, (f) higher humidity levelswhich decrease evaporative
cooling, (g) intensity of windwhich promotes evaporative cooling,
and (h) the physical condition of the person. 6. Ask students to
explain how blood vessel constriction at the body surface,
shivering, and a general increase in metabolism help a person to
keep warm in a cold environment. 7. Tylenol (acetaminophen) is
often used to reduce fevers. Discuss with your students the
advantages and disadvantages of using drugs to lower a fever. 8.
Students might better understand the problems faced by freshwater
fish if you relate it to what occurs when they soak their hands in
water. Students will likely recall that their skin wrinkles when
soaked in water. Some may have noticed that their hands wrinkle
even faster in soapy water. Skin absorbs water by osmosis (just as
a freshwater fish gains water). Oils on our skin reduce the influx
of water. Thus soapy water, which washes away these oils, speeds up
the process. The wrinkling occurs because the skin can expand only
in certain areas, creating puckers. 9. A moderately full human
urinary bladder holds about 500 ml (or 1 pint) of fluid. The
maximum capacity of the bladder may reach double that volume,
although when overdistended, it can burst! 10. The unfortunate
shortage of kidneys and other organs available for transplant is a
major health issue. Consider sharing this issue with your class.
Many state and federal organ donation organizations can be located
by a quick Internet search. The National Kidney Foundation site
(www.kidney.org/) includes information on kidney donation. 49
Response: Heating Thermostat stops (control center) turns heater
off
Figure 21.13 Response: Heating stops Thermostat (control center)
turns heater off Stimulus: Roomtemperature is above set point Room
temperature drops Set point: Room temperature 20C (68F) Stimulus:
Roomtemperature is below set point Room temperature rises
Thermostat (control center) turns heater on Response: Heating
starts Figure An example of negative feedback: control of room
temperature Negative and Positive Feedback
Less common is positive feedback, in which the results of a process
intensify that same process, such as uterine contractions during
childbirth. 2013 Pearson Education, Inc. Student Misconceptions and
Concerns 1. The concept of homeostasis may be new to many students,
who have never considered how organisms maintain their structure
and physiology. Analogies to other systems that engage in
self-regulation (noted in the text and below) can help. 2. The
kidneys role in filtration and selective reabsorption may initially
be confusing to many students. The process is a bit like cleaning
up a closet by removing all the contents and then selectively
refilling the closet with what you wish to store. Teaching Tips 1.
Challenge your students to think of other examples of negative and
positive feedback. Students from diverse disciplines may think of
many new examples, including mechanisms in an automobile. 2. The
terms warm-blooded and cold-blooded are less precise than endotherm
and ectotherm. Encourage students to discuss why endotherm and
ectotherm are preferred. 3. Ask your students to explain the
adaptive advantages of endothermy and ectothermy. You might prompt
the discussion by noting that endotherms consume about 10 times as
many calories as ectotherms of equivalent body mass. What might be
the advantages worth this additional cost for endotherms? 4. Heat
generation resulting from aerobic metabolism is analogous to heat
generation in the engine of an automobile. In both cases, the heat
is a by-product of the process. In the winter, this excess heat
helps keep the body and an automobile warm. In the summer, both the
body and the automobiles engine must work to keep from overheating.
5. Have students list the many factors that affect heat gain and
loss during times of physical activity. These include (a) the age
of the personyounger people tend to have higher metabolic rates,
(b) the level of physical activityaerobic metabolism increases to
generate ATP to move muscles, (c) proper hydration to permit
adequate sweating, (d) the color of the persons clothing, (e) the
intensity of sunlight, (f) higher humidity levelswhich decrease
evaporative cooling, (g) intensity of windwhich promotes
evaporative cooling, and (h) the physical condition of the person.
6. Ask students to explain how blood vessel constriction at the
body surface, shivering, and a general increase in metabolism help
a person to keep warm in a cold environment. 7. Tylenol
(acetaminophen) is often used to reduce fevers. Discuss with your
students the advantages and disadvantages of using drugs to lower a
fever. 8. Students might better understand the problems faced by
freshwater fish if you relate it to what occurs when they soak
their hands in water. Students will likely recall that their skin
wrinkles when soaked in water. Some may have noticed that their
hands wrinkle even faster in soapy water. Skin absorbs water by
osmosis (just as a freshwater fish gains water). Oils on our skin
reduce the influx of water. Thus soapy water, which washes away
these oils, speeds up the process. The wrinkling occurs because the
skin can expand only in certain areas, creating puckers. 9. A
moderately full human urinary bladder holds about 500 ml (or 1
pint) of fluid. The maximum capacity of the bladder may reach
double that volume, although when overdistended, it can burst! 10.
The unfortunate shortage of kidneys and other organs available for
transplant is a major health issue. Consider sharing this issue
with your class. Many state and federal organ donation
organizations can be located by a quick Internet search. The
National Kidney Foundation site (www.kidney.org/) includes
information on kidney donation. 51 Thermoregulation
Thermoregulation is the maintenance of internal body temperature.
Endotherms such as mammals and birds derive the majority of their
body heat from their metabolism. 2013 Pearson Education, Inc.
Student Misconceptions and Concerns 1. The concept of homeostasis
may be new to many students, who have never considered how
organisms maintain their structure and physiology. Analogies to
other systems that engage in self-regulation (noted in the text and
below) can help. 2. The kidneys role in filtration and selective
reabsorption may initially be confusing to many students. The
process is a bit like cleaning up a closet by removing all the
contents and then selectively refilling the closet with what you
wish to store. Teaching Tips 1. Challenge your students to think of
other examples of negative and positive feedback. Students from
diverse disciplines may think of many new examples, including
mechanisms in an automobile. 2. The terms warm-blooded and
cold-blooded are less precise than endotherm and ectotherm.
Encourage students to discuss why endotherm and ectotherm are
preferred. 3. Ask your students to explain the adaptive advantages
of endothermy and ectothermy. You might prompt the discussion by
noting that endotherms consume about 10 times as many calories as
ectotherms of equivalent body mass. What might be the advantages
worth this additional cost for endotherms? 4. Heat generation
resulting from aerobic metabolism is analogous to heat generation
in the engine of an automobile. In both cases, the heat is a
by-product of the process. In the winter, this excess heat helps
keep the body and an automobile warm. In the summer, both the body
and the automobiles engine must work to keep from overheating. 5.
Have students list the many factors that affect heat gain and loss
during times of physical activity. These include (a) the age of the
personyounger people tend to have higher metabolic rates, (b) the
level of physical activityaerobic metabolism increases to generate
ATP to move muscles, (c) proper hydration to permit adequate
sweating, (d) the color of the persons clothing, (e) the intensity
of sunlight, (f) higher humidity levelswhich decrease evaporative
cooling, (g) intensity of windwhich promotes evaporative cooling,
and (h) the physical condition of the person. 6. Ask students to
explain how blood vessel constriction at the body surface,
shivering, and a general increase in metabolism help a person to
keep warm in a cold environment. 7. Tylenol (acetaminophen) is
often used to reduce fevers. Discuss with your students the
advantages and disadvantages of using drugs to lower a fever. 8.
Students might better understand the problems faced by freshwater
fish if you relate it to what occurs when they soak their hands in
water. Students will likely recall that their skin wrinkles when
soaked in water. Some may have noticed that their hands wrinkle
even faster in soapy water. Skin absorbs water by osmosis (just as
a freshwater fish gains water). Oils on our skin reduce the influx
of water. Thus soapy water, which washes away these oils, speeds up
the process. The wrinkling occurs because the skin can expand only
in certain areas, creating puckers. 9. A moderately full human
urinary bladder holds about 500 ml (or 1 pint) of fluid. The
maximum capacity of the bladder may reach double that volume,
although when overdistended, it can burst! 10. The unfortunate
shortage of kidneys and other organs available for transplant is a
major health issue. Consider sharing this issue with your class.
Many state and federal organ donation organizations can be located
by a quick Internet search. The National Kidney Foundation site
(www.kidney.org/) includes information on kidney donation. 52
Thermoregulation Ectotherms
such as most invertebrates, fishes, amphibians, and nonbird
reptiles obtain body heat primarily by absorbing it from their
surroundings. 2013 Pearson Education, Inc. Student Misconceptions
and Concerns 1. The concept of homeostasis may be new to many
students, who have never considered how organisms maintain their
structure and physiology. Analogies to other systems that engage in
self-regulation (noted in the text and below) can help. 2. The
kidneys role in filtration and selective reabsorption may initially
be confusing to many students. The process is a bit like cleaning
up a closet by removing