BSCS Biology:
A Human Approach
Fourth edition, © 2011 by BSCS
Unit 2 Overview
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A
mong the principles that unify
the diverse forms of life on
Earth is the ability of organisms
to maintain an internal dynamic
balance. Throughout unit 2,
­Homeostasis: Maintaining Dynamic
Equilibrium in Living Systems, students
will learn how living systems maintain
internal balance. This balance is
essential for an organism to accommodate changes in the surrounding
environment and to sustain life. Using
characteristics of human body systems
as examples for comparison, students
will ­investigate the concept of internal
balance.
Students will begin the unit with
chapter 4, The Internal Environment of
Organisms, by exploring the concepts
of internal environments, external
environments, compartments, and
membranes. Next, students will
investigate different systems in the
human body, from the level of the
cell to the body as a whole, to learn
ways the human body maintains an
internal balance. Then in chapter 5,
Maintaining Balance in Organisms,
students will extend their opportunity
to learn about internal balance in the
human body by applying the concept
to some of the basic activities of life.
In chapter 6, Human Homeostasis:
Health and ­Disease, students will study
what happens when internal balance
is disrupted in various ways. They also
will consider how humans can influence, both p
­ ositively and negatively,
their own health as well as the health
of others.
This unit provides opportunities
for students to enhance their use of
inquiry skills such as making and testing predictions and constructing and
using models. The students also have
an opportunity to examine the nature
of science as it applies to certain
aspects of the history of medicine. The
Science and Humanity subtheme is
prominent in chapter 6.
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Y
our body is constantly working to maintain a
balanced, functioning state. Under normal
conditions, this balancing act is an intricate,
dynamic process that your body takes care of with
little conscious effort. Think of a skier gliding over
the water. Not only does she balance on the edge of
her ski, but her body also maintains a balance in
other, less obvious ways. Although cool water
surrounds her, her body temperature remains within
a relatively narrow range. As she exerts energy to
maintain her balance over rough water or to hold
her position in a curve, her heart and breathing rates
also adjust to bring more oxygen to the cells of her
body. In addition to temperature and oxygen levels,
her body continuously balances numerous other
factors to keep them all within healthy limits. The
skier’s body is working to maintain a balanced
internal environment. Her body is maintaining
homeostasis.
In unit 2, Homeostasis: Maintaining Dynamic
Equilibrium in Living Systems, you will examine some
of the processes involved in maintaining balance in
the human body. You will consider the components
of the human body that allow the regulation of
internal conditions. You also will apply what you
have learned to study how the human body reacts
when this balance is disrupted significantly.
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Prior Conceptions
Students’ understanding of dynamic
equilibrium, or homeostasis, must
include both comprehension of the
various elements involved and the
ability to relate these processes to one
another.
Much of the students’ prior
­knowledge of the concept of homeostasis likely will be in the context of
disease, in which balance is disrupted.
According to the research into the
benchmarks, upper-elementary students may believe that “germs” cause
all illnesses (American Association for
the Advancement of Science [AAAS],
2001). However, research also shows
that as students grow older, their
understanding and beliefs include
Unit 2 Homeostasis: Maintaining Dynamic Equilibrium in Living Systems
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the idea that illness can be caused
by malfunctioning internal organs
and systems, poor health habits, and
genetics (AAAS, 2001). Related to this,
students may also have the idea that
most bacteria cause illness (Williams,
1991), but their knowledge should
include information on b
­ acteria that
help maintain h
­ omeostasis in processes like digestion.
It is important to ensure that
­students understand the role and
meaning of homeostasis in relation to
other typical body processes as well.
One misconception students may have
is that homeostasis represents a particular number or fixed value. For example, they may feel that blood sugar
must return to a specific value after
U N I T
2
Homeostasis:
Maintaining Dynamic
Equilibrium in
Living Systems
By the end of unit 2, you should be
able to understand that
✔ All organisms, organ systems, and
cells are affected by interactions
between their internal and
external environments;
✔ Organisms’ internal systems
maintain a dynamic balance
called homeostasis;
✔ Stressors may overwhelm the
ability of organisms to maintain
homeostasis; and
✔ Behaviors and physiological
responses help maintain
homeostasis.
UNIT CONTENTS
4 The Internal Environment
of Organisms
5 Maintaining Balance in Organisms
6 Human Homeostasis: Health
and Disease
4
5
Advance Preparation for
the Unit
You also will learn to
✔ write a hypothesis,
✔ design a controlled experiment,
✔ develop an explanation, and
✔ perform ethical analyses.
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Unit Goals
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eating, at which point the level has
returned to homeostasis (­Westbrook,
1992).
Teachers can help students learn
about homeostasis by breaking
down the process into the different
variables, allowing students to gain
comprehension of each of these elements separately, and relating the
elements to provide the big picture of
the process. Homeostasis is a concept
that students are often expected to
learn without the benefit of concrete experience. In unit 2, student
investigations build upon each other,
which allows students to develop a
concrete but increasingly sophisticated understanding of this abstract
­physiological ­phenomenon (Westbrook, 1992).
Before you begin unit 2, create new
cooperative teams of 4 students.
­During this unit, the students may
work in teams of various sizes, but
their core team should consist of
4 students.
You may want to review the
unit’s video segments and the
activities that involve probe
ware systems before you have the
students work with them in class.
You will need to use microscopes
in this unit. Review the activities
in ­chapters 4, 5, and 6 for materials
you may need to order in advance.
You may also want to reserve a computer lab for students to carry out the
­animation activities in chapter 4.
Unit Extension
Because this unit focuses on human
examples of homeostasis, you may
want to add information on plants
and viruses found in appendix F in the
student text.
Unit 2 Homeostasis: Maintaining Dynamic Equilibrium in Living Systems
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