BSCS Biology: A Human Approach

Fourth edition, © 2011 by BSCS

Unit 2 Overview

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204 Unit 2 Homeostasis: Maintaining Dynamic Equilibrium in Living Systems

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204 204

Your 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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54 6

2U N I T

205

Homeostasis:Maintaining Dynamic

Equilibrium in Living Systems

UNIT CONTENTS

4 The Internal Environment of Organisms

5 Maintaining Balance in Organisms6 Human Homeostasis: Health

and Disease

205

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.

You also will learn to

✔  write a hypothesis,

✔  design a controlled experiment,

✔  develop an explanation, and

✔  perform ethical analyses.

LaurelTech/KH Design Pass First Pass Second Pass PDF Pass

204 204

Your 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.

LaurelTech/KH Design Pass First Pass Second Pass PDF Pass

54 6

2U N I T

205

Homeostasis:Maintaining Dynamic

Equilibrium in Living Systems

UNIT CONTENTS

4 The Internal Environment of Organisms

5 Maintaining Balance in Organisms6 Human Homeostasis: Health

and Disease

205

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.

You also will learn to

✔  write a hypothesis,

✔  design a controlled experiment,

✔  develop an explanation, and

✔  perform ethical analyses.

Among 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 accommo-date 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 influ-ence, both positively 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 test-ing 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.

Prior ConceptionsStudents’ 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 homeo-stasis likely will be in the context of disease, in which balance is disrupted. According to the research into the benchmarks, upper-elementary stu-dents 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

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 bacteria that help maintain homeostasis in pro-cesses 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 partic-ular number or fixed value. For exam-ple, they may feel that blood sugar must return to a specific value after

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Your 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.

LaurelTech/KH Design Pass First Pass Second Pass PDF Pass

54 6

2U N I T

205

Homeostasis:Maintaining Dynamic

Equilibrium in Living Systems

UNIT CONTENTS

4 The Internal Environment of Organisms

5 Maintaining Balance in Organisms6 Human Homeostasis: Health

and Disease

205

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.

You also will learn to

✔  write a hypothesis,

✔  design a controlled experiment,

✔  develop an explanation, and

✔  perform ethical analyses.

Unit 2 Homeostasis: Maintaining Dynamic Equilibrium in Living Systems 205

LaurelTech/KH Design Pass First Pass Second Pass PDF Pass

204 204

Your 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.

LaurelTech/KH Design Pass First Pass Second Pass PDF Pass

54 6

2U N I T

205

Homeostasis:Maintaining Dynamic

Equilibrium in Living Systems

UNIT CONTENTS

4 The Internal Environment of Organisms

5 Maintaining Balance in Organisms6 Human Homeostasis: Health

and Disease

205

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.

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

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 ele-ments 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 con-crete experience. In unit 2, student investigations build upon each other, which allows students to develop a concrete but increasingly sophisti-cated understanding of this abstract physiological phenomenon (West-brook, 1992).

Advance Preparation for the UnitBefore 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 com-puter lab for students to carry out the animation activities in chapter 4.

Unit ExtensionBecause 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.