UNIT 1

Living Systems
Lesson 1: Life in the Earth System . . . . 4

Lesson 2: Organisms: Cells

to Body Systems . . . . . . . . . . . . . . . . . .16

Lesson 3: Mechanisms
of Homeostasis . . . . . . . . . . . . . . . . . . .32

Lesson 4: Bioengineering . . . . . . . . . .48

Thing Explainer: Bags of

Stuff Inside You . . . . . . . . . . . . . . . . . . .62

Unit Connections. . . . . . . . . . . . . . . . . .66

Unit Review . . . . . . . . . . . . . . . . . . . . . . .67

Unit Performance Task . . . . . . . . . . . . .69

Image Credits: ©Living Art Enterprises/Science Source

The human heart is one component

in a larger living system.

2 Unit 1 Living Systems

 FIGURE 1: Each bat is a living system.

Living and nonliving systems are all around you. Nonliving systems help you complete
many tasks, such as cars and buses to travel to school or cell phones to make a call.
Organisms, such as bats, are examples of living systems. Cells in bats work together to
perform all of the functions necessary for life. For example, structures in bats’ wings
help them maintain water balance in their bodies. Bats and other living and nonliving
things are part of larger systems on Earth.

Predict How do you think living systems such as bats carry out life functions and
respond to changes in the environment?

DRIVING QUESTIONS

As you move through the unit, gather evidence to help you answer the following
questions. In your Evidence Notebook, record what you already know about these
topics and any questions you have about them.
1. What are the levels of organization within the Earth system?
2. How do systems in living things interact to maintain the organism?
3. How does the structure of cells relate to different functions and specialization?
4. How have advances in technology influenced human health and society?
Image Credits: ©Visionary Earth/Shutterstock

UNIT PROJECT

Go online to download
Investigating Plant Systems the Unit Project
Worksheet to help
plan your project.
A seedling is a living system made up of different components. Grow seedlings and
investigate how they interact with other systems to survive and grow in changing
conditions. Can you explain the levels of organization within your seedlings and the
environment, from cells to ecosystem?

Unit 1 Living Systems 3

 1.1

Life in the Earth System

CAN YOU EXPLAIN IT?

FIGURE 1: Although the robot in this image is conceptual, robots can be programmed to
Certain conditions make life carry out very complex tasks, such as playing a game of chess.
sustainable on Earth.

Image Credits: (t) ©StockTrek/Photodisc/Getty Images; (b) ©Blutgruppe/Corbis

Gather Evidence Humans have used technology since early times. Today we may be quick to name
As you explore the lesson, cellular phones and computers as examples. However, technology includes even
gather evidence to make a claim simple things, such as a fork or a pen, basically any tool, process, or system that is
about what defines a living system. designed to solve a problem.
Robotic technology has advanced to human-like form. Robots can perform
work, including tasks that are difficult or dangerous, but they also can provide
companionship and health care. Consider the players in this chess game. The robot
and the human have parts that perform similar functions and have a control center to
guide their actions. They are both systems that can perform many of the same tasks.

Predict Imagine a company that sells robots like the one shown in Figure 1. The
company makes the claim: “This living machine is the perfect companion.” Make a case
to either support or refute this claim. How similar are living and nonliving systems?

4 Unit 1 Living Systems

EXPLORATION 1

Systems and System Models

Throughout history, humans have strived to understand the world around us. To
help make sense of the observed phenomena, we organize information and identify
patterns. One approach to understanding natural phenomena is called systems
thinking. This way of thinking examines links and interactions between components,
or parts of a system, to understand how the overall system works.

Properties of Systems
A system is a set of interacting components considered to be a distinct entity for the
purpose of study or understanding. The robot and human at the beginning of the
lesson are both systems.

camera FIGURE 2: To Collaborate Discuss

send a text this question with a
message, a cellular partner: What systems could you
phone requires define in the world around you?
components, such
as a signal receiver
and transmitter, a
microphone battery, a circuit
board, and a
screen
screen.
circuit battery
board

connector
and
antenna

Boundaries and Components

Analyze What is the
Boundaries define the space of the system to separate that system from the rest of the
boundary of the human
universe. A cellular phone is a system of electronics contained in a protective covering.
body? What is the boundary of a
The components are all the parts of the system that interact to help the system carry
out specific functions. For example, a cellular phone needs the parts described in robot? Compare the inputs and
Figure 2 to function properly. Together, the components send and receive radio outputs of humans and robots in
signals and transform them into useful communication, such as text messages. terms of matter and energy.

Inputs and Outputs

The inputs and outputs of different types of systems include energy, matter, and
information. Outputs are generated when the inputs are processed in some way. In the
case of a cellular phone, a radio signal (an input) is converted to vibrations (an output)
that you detect as sound.

Lesson 1 Life in the Earth System 5

 Open and Closed Systems
Systems can be categorized according to the flow of inputs and outputs. In an open
system, the inputs and outputs flow into and out of the system. In a closed system, the
flow of one or more inputs and outputs is limited in some way. An isolated system is a
system in which all of the inputs and outputs are contained within the system.

Analyze Is the human body an open, closed, or isolated system? What about a
robot? Explain your answer.

Controls
The components of a system include the controls that help keep the system working
properly by monitoring and managing the inputs and outputs. Controls can be
automatic, manually set, or a combination of both. An important system control is
feedback. Feedback is information from one step of a cycle that acts to change the
behavior of a previous step of a cycle. So, feedback is output that becomes input. A
feedback loop is formed when an output returns to become an input in the same
system that generated the output.

Systems and System Models

Model Draw a simple

FIGURE 3: A thermostat can be used to control the heating and cooling systems
diagram showing how a
in a home.
thermostat would respond
when the temperature in a
room rises above the set point.

Some air conditioners and heaters have a control system called a thermostat, such
as the one shown in Figure 3. A thermometer inside the thermostat continually
measures the temperature in the room. If the air temperature in the room rises
above a preset temperature, the thermostat signals the air conditioner to turn on. If
the air temperature in the room falls below the preset temperature, the thermostat
Image Credits: ©iStock/Getty Images Plus/koinseb

signals the air conditioner to turn off.

6 Unit 1 Living Systems

 System Organization
Systems can range in size and in complexity. For example, a thermostat is a small,
relatively simple system. The chess-playing robot is a larger, very complex system. The
Earth system is larger still and is itself a part of the solar system, the Milky Way galaxy,
and the universe.
More complex systems generally have more levels of organization than simpler
systems. For example, organisms, or living things, are systems made up of smaller
systems, such as organs, tissues, and cells. Two organisms that interact also can
make up a system, such as a bird that pollinates a plant. On a larger scale, you are a
system that is part of an ecosystem, or community of organisms, and their physical
environment. You also are part of the larger Earth system.

FIGURE 4: Both the hummingbird and the thistle plant are systems that interact with one
another. They are part of an ecosystem, such as a city park.
Image Credits: (tl) ©Don Mammoser/Shutterstock; (tr) ©Ben Blankenburg/Fotolia; (b) ©Photographer’s Choice RF/Georgette Douwma/Getty Images

As mentioned earlier, an output of a system can feed back into the system, changing Gather Evidence
how the system may respond. Similarly, an output of one system can act as an input How do your interactions
to a completely different, perhaps even unrelated, system. Think about walking into with nonliving systems affect your
an air-conditioned building on a hot day. The cool air becomes an input to your body environment?
system as receptors in your skin detect the change in air temperature. You may even
begin to shiver slightly: the body’s response when it senses cold temperatures.

FIGURE 5: A scuba diver and the scuba gear she wears are two systems interacting.

Explain The scuba diver is a living system. The scuba gear, or self-contained
underwater breathing apparatus, is a system of air exchange. How are these two
systems interacting?

Lesson 1 Life in the Earth System 7

 System Models
Suppose that an engineering team is designing a new airplane. If they were to build
a full-sized airplane for a performance test of each different design, the cost and the
time would be impractical. A more practical option would be to use a smaller scale
Model Develop a short model of the airplane to study and analyze the various components of the system. A
list of systems that you model is a pattern, plan, representation, or description designed to show the structure
think biologists would want to or workings of an object, system, or concept. You might think of a model simply as
model. Choose one system from a smaller scale physical representation of a larger system. However, models are not
your list and develop a plan for how limited to physical objects. Other types of models include computer simulations,
you would model it. conceptual diagrams, and mathematical equations, as shown in Figure 6.

FIGURE 6: Types of Models

Protein Synthesis y = a(1 + r)x

y = final population
DNA → RNA → Proteins a = initial population
r = growth rate
x = number of time
intervals passed

a Physical Model b Conceptual Model c Mathematical Model d Simulation

A smaller or larger copy of A diagram or flow chart An equation or set of Often in the form of a

Image Credits: (l) ©alice-photo/Shutterstock; (r) Image of PDB entry 3L4V created with Chimera (http://www.rbvi.ucsf.edu/chimera/)
an object. Physical models that shows how parts of a equations that generate computer model. Can be
also can be built to scale. system are related or how a data related to how a used to test variables and
Scale is the proportional process works. system or process works. observe outcomes.
relationship between a Mathematical models
model’s measurements play a significant role in
and the real object’s computer models.
measurements.

Systems Biology
We can apply systems thinking to biology. Systems biology studies biological systems
as a whole. This approach allows scientists to consider biological phenomena at
different scales and examine how the components of a biological system interact.
By considering the larger picture, biologists are better able to identify emergent
properties of the system. An emergent property is a property that a system has but
that its component parts do not have. For example, cells are self-contained systems
that can function independently. However, when combined, similar cells form tissue,
which can perform unique functions that the individual cells could not.
Language is a more recognizable example of a system with emergent properties.
Its basic components are the sounds that combine to form words. The emergent
properties are the meanings of the words made from these sounds when placed into
sentences. The sentences and paragraphs convey meaning the words and sounds
making up the words cannot individually.

8 Unit 1 Living Systems

 Similarly, DNA is a molecule that carries the genetic code of all organisms. The code
consists of just four bases represented with the letters A, T, G, and C. The sequence
of these bases in DNA provides coded instructions for making thousands of different
proteins. Each protein is made of a specific arrangement of amino acids coded for by
DNA. The emergent property of DNA is the information that codes for proteins.

FIGURE 7: A systems approach in scientific research of diseases, Explore Online

such as Parkinson’s disease, requires collaboration among many different areas of science.

Neurochemistry Medicine

Genomics Bioinformatics

SYSTEMS
BIOLOGY

Environmental Biophysics
Science

Molecular
Proteomics
Biology

Parkinson’s disease (PD) is an aging-related degeneration of nerve cells in the brain Language Arts
Image Credits: (t) ©GJLP/Science Source; (r, b) ©Wesley Peng; (l) ©iStock/Getty Images Plus/Svisio

that causes progressive slowness of movement. Many factors can contribute to PD. For Connection Work with
example, PD often involves proteins that become misfolded, which interferes with the a group to research one of these
protein performing its normal function within the cell. The build up of these misfolded fields and its contribution to PD
proteins causes additional damage.
research. Share your research with
Many different scientific and mathematical disciplines contribute to PD research other groups in your class.
with the goal of coming to a complete understanding of the disease. For example,
biophysics applies laws of physics to biological phenomena. Some biophysicists study
the structural changes of a brain protein called alpha-synuclein and its influence
on PD. Typically, alpha-synuclein is unfolded, but in certain conditions it becomes
highly folded, contributing to PD. Understanding why a protein misfolds may involve
investigating how the DNA transmitted the code when building that protein. Was
there a mistake in the code? Or does something happen to the protein after coding
occurs? Genomics research helps to answer these kinds of questions.

Explain Describe how different types of models could be used to research a disease.
Make a list of questions you would ask. Categorize your questions into different fields of
science that might be involved in the research.

Lesson 1 Life in the Earth System 9

 EXPLORATION 2

The Earth System

To understand living things better, we can study the systems in which they exist. One
System Models
of these systems is our home planet—Earth. The Earth system is all of the matter,
energy, and processes within Earth’s boundary. Earth is made up of smaller systems,
FIGURE 8: Model of the Earth such as the biosphere, where all living things exist and interact. The biosphere in
system. turn includes many smaller subsystems of living things in both aquatic and land
environments. Earth itself exists within larger systems, such as the solar system and the
Milky Way galaxy.
As Figure 8 shows, matter stays within the Earth system, but energy enters the system
in the form of sunlight and exits in the form of heat. Within the system itself, light
energy is converted into other forms of energy that drive transformations of matter
from one form to another as it cycles through the system.

Organization of the Earth System

Explain Is Earth an open,
closed, or isolated system? Scientists use a system model to better understand interactions within the Earth
Explain. system. The system model, shown in Figure 9, organizes the Earth system into
four interconnected systems, or spheres: geosphere, hydrosphere, biosphere, and
atmosphere.
The geosphere is all the solid features of Earth’s surface, such as mountains, continents,
and the sea floor, as well as everything below Earth’s surface. The hydrosphere is all
of Earth’s water, including water in the form of liquid water, ice, and water vapor. The
biosphere is the area of Earth where life exists. The atmosphere is all of the air that
envelops Earth’s solid and liquid surface.

FIGURE 9: Scientists
organize the Earth atmosphere
system into four
spheres.

biosphere

hydrosphere geosphere

Explain This model shows the biosphere in the middle of the diagram with arrows
connecting it to the other spheres. Why is the biosphere depicted this way?

10 Unit 1 Living Systems

 Organization of the Biosphere
Earth’s biosphere is made up of ecosystems. An ecosystem includes all of the nonliving
and living things, or organisms, in a given area. Nonliving things include the climate,
soil, water, and rocks that organisms rely on for survival. The relationships among
organisms can be further categorized. Organisms of the same species that live in the
same area make up a population. The collection of the different populations in an area
make up a community. Communities exist within larger systems called biomes. Biomes
are major regional or global areas characterized by their climate and vegetation.
Examples of biomes include deserts, tropical rain forests, tundra, and grasslands.

FIGURE 10: The Florida Everglades is an example of an aquatic ecosystem.

Model Place these terms
in order to illustrate the
levels of scale from an organism to
biosphere
the solar system: population,
biosphere, solar system, ecosystem,
biome
organism, biome, Earth, community.

ecosystem
Explore Online
community
Hands-On Lab

Life Under a Microscope

Observe pond water under a
microscope and determine whether
population items are living or nonliving based
on their observable characteristics.
individual

The living components in an ecosystem are called biotic factors. The nonliving
components of ecosystems are abiotic factors. The biotic and abiotic components in
an ecosystem interact and are interdependent.

FIGURE 11: Taiga is a biome characterized by long, cold winters and short, mild, and
rainy summers.

Model Identify the biotic

Image Credits: (b) ©age fotostock/Frank Pali/Getty Images

and abiotic factors in

Figure 11. Make a model to
illustrate how these factors interact
in this ecosystem.

Lesson 1 Life in the Earth System 11

 Characteristics of Living Things
Scientists use a set of characteristics to define living things. In general, all living things
are made up of one or more cells, require an energy source, grow and change over
time, reproduce by making copies of themselves or by having offspring, and respond
to changes in their environment. Homeostasis is the maintenance of constant internal
conditions in an organism. Although temperature and other environmental conditions
are always changing, the conditions inside organisms usually stay quite stable.
Maintaining stable internal conditions is critical to an organism’s survival.
Explore Online
FIGURE 12: Most plants get nitrogen from the soil.
Venus flytraps grow in nitrogen-poor soil and must rely on the insects they catch
as their source of nitrogen.

Analyze Describe at least

two biological systems.
Explain how these systems are
independent from and
interconnected with each other.

The Venus flytrap in Figure 12 is a living thing. It is a plant made up of individual

cells that work together to perform the functions it needs to survive. It gets its
energy from the sun and the nutrients it needs from the insects it digests. A Venus
flytrap reproduces both sexually through pollination and asexually by spreading its
rhizomes—rootlike stems—underground in the soil.

Explore Online How scientists think about the characteristics of living things has undergone revision
as new evidence comes to light. For example, there is disagreement about whether
Hands-On Lab
or not viruses are alive. Viruses do not maintain homeostasis and cannot reproduce
The Study of Life Plan and without a host organism.
conduct an investigation to Another way to think about life is as an emergent property of a collection of certain
determine how different factors nonliving things. As an example, proteins are chemical building blocks in all organisms,
affect the number of living things but proteins by themselves are nonliving things. However, proteins in combination
Image Credit: ©Francesco Tomasinelli/Science Source

found in a soil sample. with other molecules and a complex set of reactions make up living things. This
argument applies to viruses, which are made only of a strand of genetic material
surrounded by a protein coat. As a result, some scientists claim viruses are not living
things, because they are not made of cells. However, there are some membrane-bound
viruses. Are viruses living things or not? The debate continues.

Explain Record evidence for whether the robot at the beginning of this lesson meets
the criteria for a living system. Which criteria does it meet, and which does it not? Does a
robot have emergent properties? Explain your answer.

12 Unit 1 Living Systems

 CONTINUE YOUR EXPLORATION

Engineering

Modeling a System

FIGURE 13: Your school cafeteria can be modeled as a system.

Identify the System
Whether you think about it or not, you interact with
systems every day. A school, a classroom, or an
athletic team could be modeled as a system. In this
activity, you will model a system that you are familiar
with, and then use your model to suggest improvements
to that system. You can choose one of the following
school-related systems or come up with one of your own:
• getting food in the cafeteria
• visitors checking in at the front office
• students getting on buses to go home
• cars leaving the parking lot when school is over
You may work on your system model on your own or in
collaboration with one or more students.

Make a Model
Make a model of the system you have chosen. Your
Consider Tradeoffs
model should illustrate the following:
• the components of the system Choose one of the solutions you suggested, and answer this
• how the components interact question: How would this proposed solution affect the other
• the inputs and outputs of the system parts of the system?
• the system boundaries Are there any social, cultural, or environmental impacts of
• system controls and feedback loops your solution? Explain your answer.

Identify a Problem Revise the Model

Identify a problem with this system for which you could Revise your original model to show how the solution you
suggest solutions. For example, is there congestion in suggested would be integrated into the system.
this system when too many people try to get to a location
at the same time?
Language Arts Connection Prepare a multimedia
Suggest a Solution presentation to persuade people to implement your
Image Credits: ©Monkey Business Images/Getty Images Plus

solution. A multimedia presentation should use graphics, text,

Brainstorm some solutions to this problem. How
music, video, and sound. Include your final model, an explanation
could the efficiency of this system be improved in terms
of the following items?
of the solution you are proposing, and a discussion of tradeoffs
you considered.
• time
• costs
• materials
• inputs and outputs

Go online to choose one of

VIRUSES: ARE THEY ALIVE? LIFE UNDER A MICROSCOPE
these other paths.

Lesson 1 Life in the Earth System 13

 EVALUATE

Lesson Self-Check

CAN YOU EXPLAIN IT?

FIGURE 14: Both robots and humans are complex systems.

Robots have many of the capabilities of humans, including taking in and processing
information and completing many of the same tasks as humans. Robots can be used to
complete tasks that are too dangerous or difficult for humans to complete.
Some robots are built to perform a specific task and do not resemble any sort of
organism. Other robots, though, may have human-like forms and could be used
to provide companionship or health care. When promoting one of their humanoid
robots, similar to the one in Figure 14, an imaginary robotics company claims, “This
living machine is the perfect companion.”

Explain Refer to the notes in your Evidence Notebook to explain whether or not a
robot fits the criteria of a living system. Consider the following questions when
developing your explanation:
1. Which properties of systems does the robot have, and which does it not?
2. Which properties of living things does the robot have, and which does it not?
3. What potential emergent properties could this robot have?
Image Credits: ©Blutgruppe/Corbis

For each of the above questions, include specific examples and evidence to support
your claims.

14 Unit 1 Living Systems

 CHECKPOINTS

Check Your Understanding 6. What is an emergent property?

Use the diagram to answer Questions 1–5. a. a property that a system has but that its individual
component parts do not have
FIGURE 15: This conceptual model shows the basics of how a b. a new property exhibited by a component of a system
dryer works. c. a property of an individual component but not the
system as a whole
electrical
energy d. a property that is not always exhibited by a system
desired
time heat
heating actual 7. Pick two of Earth’s spheres (biosphere, atmosphere,
timer clothes
elements dryness
geosphere, hydrosphere), and draw a model showing
(Input) error (Output) (Process) how these two systems interact. Your model should show
sensor components of these systems, at least one way these
feedback loop components interact, and inputs and outputs that move
from one system to another.

8. Is movement a characteristic of living things? Explain why

1. How does the sensor interact with the other components
this characteristic should or should not be considered a
of this system?
characteristic of living things, giving specific examples to
a. The sensor detects the heat of the clothes and makes support your claim.
the timer generate more heat.
b. The sensor detects the dryness of the clothes and then 9. Explain what a feedback loop is using the terms input,
sends information to the timer. output, and homeostasis.
c. The sensor detects whether the heating element is
functioning properly and then sends input to the
timer.
MAKE YOUR OWN STUDY GUIDE
d. The sensor detects how much time is left and sends
input to the heating element to increase or decrease
the heat. In your Evidence Notebook, design a study guide that
supports the main idea from this lesson:
2. Which of these is not a direct input for the timer in
Models can be used to illustrate the relationships between
this system?
components of living and nonliving systems.
a. time manually entered by the user
b. electrical signals from the sensor Remember to include the following information in your
c. dryness of the clothes study guide:
d. heat from the heating element • Use examples that model main ideas.
• Record explanations for the phenomena you investigated.
e. electricity from the wall outlet
• Use evidence to support your explanations. Your support can
include drawings, data, graphs, laboratory conclusions, and
3. Given the model, would you say this system is a closed
other evidence recorded throughout the lesson.
system or an open system? Explain your answer.
Consider the properties of systems and system models and how
4. Explain how the feedback loop works in this model. systems can be used to model the levels of organization within
living organisms.
5. Would a small load of laundry take longer to dry than a
larger load? Use the diagram to explain your answer.

Lesson 1 Life in the Earth System 15

 1.2

Organisms: Cells
to Body Systems

Muscle cells have a CAN YOU EXPLAIN IT?

specialized structure that
allows them to contract.
FIGURE 1: A ballerina awaits her cue backstage.

Image Credits: (t) ©Biophoto Associates/Science Source; (b) ©MUJAHID SAFODIEN/AFP PHOTO/Getty Images
Gather Evidence
As you explore this lesson,
gather evidence to explain how
systems within your body interact
to regulate overall body functions.
If you have ever performed in front of an audience, you may have experienced
the feeling of having “butterflies” in your stomach. When you have a feeling about
something going a certain way, you might describe it as a “gut feeling.” Where do
these sensations come from? Do they come from your stomach, your brain, or both?
Systems within your body interact to help you take in information, make decisions, and
carry out tasks. Sometimes these systems carry out tasks without your even knowing it,
such as pumping your blood, helping you breathe, and breaking down your food.

Predict How do you think systems within your body interact to produce sensations
like “butterflies” in your stomach?

16 Unit 1 Living Systems

EXPLORATION 1

Interacting Systems in Organisms

Over the course of a day, you complete many different tasks. Whether you are eating,
sleeping, or talking to a friend, systems within your body are interacting at different
levels. Scientists organize multicelluar organisms into five basic levels beginning with
Collaborate Describe a
cells and moving to increasingly complex structures. These five levels of organization
are shown in the human respiratory system in Figure 2. task you perform each day
that requires different systems
A tissue is a group of similar cells that work together to carry out a specific function. within your body to interact.
For example, cells in the epithelial tissue of your lungs have tiny hair-like extensions
called cilia. Together, these ciliated cells act like a conveyer belt to sweep foreign
particles and pathogens out of the lungs. Groups of tissues form organs such as the
lungs, sinuses, and nose. Each of these organs has a specialized function in the body.
Multiple organs interact to carry out whole-body functions. In the respiratory system,
the nose and sinuses filter, moisten, and warm the air before it enters the lungs.

FIGURE 2: Multicellular organisms have a hierarchical structural organization. Each

system, such as the respiratory system, is made up of interacting components.

CELL
the basic unit of life

TISSUE
similar cells that work
together to perform
a specialized function

ORGAN
a group of tissues that
carry out a specialized
function of the body Analyze How do
structures in the respiratory
system interact to protect the
lungs? How might a sinus infection
affect the rest of the respiratory
system?
ORGAN SYSTEMS
two or more organs
that work together
to perform body
functions
ORGANISM
Together, the organ systems make
up the entire organism.

Lesson 2 Organisms: Cells to Body Systems 17

 Organ Systems
An organ system is two or more organs that work together to perform body
functions. Organ systems interact to help the organism maintain internal stability, or
homeostasis. For example, the muscular system interacts with the circulatory system
to help pump your blood and deliver oxygen and nutrients to cells. Some of the
components and functions of organ systems in the human body are shown in Figure 3.

FIGURE 3: Organ Systems in the Human Body

System Organs and Other Components Primary Functions

Circulatory heart, blood vessels, blood, lymph transports oxygen, nutrients, hormones, and wastes; helps regulate
nodes, lymphatic vessels body temperature; collects fluid lost from blood vessels and returns it
to the circulatory system
Digestive mouth, pharynx, esophagus, stomach, breaks down and absorbs nutrients, salts, and water; transfers digested
small and large intestines, pancreas, materials to the blood; eliminates some wastes
gall bladder, liver
Endocrine hypothalamus, pituitary, thyroid, produces hormones that act on target tissues in other organs to
parathyroids, adrenal glands, pancreas, influence growth, development, and metabolism; helps maintain
ovaries, testes homeostasis
Excretory skin, kidneys, bladder filters blood and eliminates waste products; helps maintain
homeostasis
Immune white blood cells, thymus, spleen protects against disease; stores and generates white blood cells
Integumentary skin, hair, nails, sweat and oil glands protects against infection, UV radiation; regulates body temperature
Muscular skeletal, smooth and cardiac muscles produces voluntary and involuntary movements; helps to circulate
blood and move food through the digestive system
Nervous brain, spinal cord, peripheral nerves regulates body’s response to changes in internal and external
environment; processes information
Reproductive male: testes, penis, associated ducts produces and transports reproductive cells; provides the environment
and glands for embryonic development in females
female: ovaries, fallopian tubes,
uterus, vagina
Respiratory nose, nasal cavity, pharynx, trachea, brings in oxygen for cells, expels carbon dioxide and water vapor
lungs
Skeletal bones, cartilage, ligaments, tendons supports and protects vital organs; allows movement; stores minerals;
bone marrow is site of red blood cell production

Analyze Many organ systems interact with the circulatory system. If a person’s
circulatory system did not function properly, how might other systems, such as the
respiratory and digestive systems, be affected? How would homeostasis, or internal
stabilty, be affected by these system imbalances?

18 Unit 1 Living Systems

Organs
Organ systems can carry out complex functions, because they are made up of organs
that work together within the system. An organ is a group of tissues that carry out a
specialized function of the body. Figure 4 shows the organs in the digestive system.

Explore Online
FIGURE 4: Organs are components that make up a body system, such as the digestive
system. In general, an organ system is made up of organs specific to the function of Hands-On Lab
that system.
Connecting Form to
Function Examine a slice of the
roots, stems, and leaves of a plant
to explain how their structures
relate to their functions.
mouth
esophagus

liver
stomach
gall bladder pancreas

large intestine small intestine

rectum/anus

The digestive system is a collection of organs that breaks down food into nutrients Predict How might the
and energy that can be used by cells. When you eat, the mouth breaks down food digestive system and the
mechanically by chewing, and proteins called enzymes in your saliva break down immune system interact to help
food chemically. Muscles in the esophagus contract to move the chewed food to the protect the body?
stomach. The stomach then uses both mechanical and chemical digestion to break
down food into nutrient components that the body absorbs and uses. As muscles
in the stomach churn food, it continues to be broken down by gastric juice, which
consists of mucus, enzymes, and acid.
The partly digested food passes into the small intestine, where additional digestion
takes place. Organs such as the liver and pancreas secrete chemicals into the upper
small intestine. These chemicals break food particles into individual nutrients, which
are absorbed through the walls of the small intestine and pass into the blood. Any
food that remains undigested passes into the large intestine where excess water is
absorbed before the solid waste is excreted from the body.

Systems and System Models Make a simple flow chart to illustrate how the
organs of the digestive system interact to help you digest food.

Lesson 2 Organisms: Cells to Body Systems 19

 Tissues
For an organ such as the stomach to carry out its function of breaking down food,
different tissues must work together. A tissue is a group of similar cells that work
together to perform a specialized function, usually as part of an organ. In the human
body, organs are made up of four general types of tissues—epithelial, connective,
muscle, and nervous tissue.

FIGURE 5: Organs such as the stomach are made up of four main types of tissues.

epithelial tissue
provides protective
lining; allows for
transport, secretion,
and absorption

connective tissue
Gather Evidence A supports, binds
together, and
tendon is a band of tissue protects other
that attaches a muscle to another tissues and organs

body part such as a bone. Which

type of tissue would tendons most muscle tissue
likely contain? contracts to allow
for movement,
support, and
heat production

nervous tissue
receives and
transmits impulses;
processes
information

Tissues in the stomach help it carry out its function in the body. Signals from nervous
tissue stimulate muscle tissue in the stomach to contract. The walls of the stomach
contain three layers of muscle tissue that contract about every 20 seconds. The muscle
tissue in the stomach contracts involuntarily, without you having to think about it.
The epithelial lining of the stomach is made up of cells that secrete stomach acid and
absorb nutrients. The type of epithelial tissue that lines the stomach has column-
shaped cells. This type of tissue provides a large amount of surface area for absorption
and secretion.
Connective tissue provides support and protection for structures in the body. Some
types of connective tissue are fibrous and tough. Other types, such as loose connective
tissue, provide support to internal organs and the surrounding blood vessels. The
connective tissue that surrounds blood vessels has the property of elasticity. This is
important, because as blood pumps through the circulatory system, the vessels within
this system must stretch to accommodate blood flow.

Analyze How does nervous tissue interact with muscular tissue in the stomach to
break down food? Why is it important for the nervous and digestive systems to work
together?

20 Unit 1 Living Systems

 Cells and Cell Differentiation
Humans, like other multicellular organisms, are collections of specialized cells
that work together. A cell is the most basic unit of life. The cells that make up an
organism arise from a single cell that goes through successive divisions to make
new cells. Cell differentiation is the process by which cells become specialized in
structure and function.

FIGURE 6: All cells in a multicellular organism arise from a single cell. As the organism Engineering
develops, cells take on unique structures that help them carry out specialized functions.
Nanobots are microscopic robots
built on the scale of a nanometer.
smooth epithelial cells
Engineers are designing nanobots
Image Credits: (tl) ©Biophoto Associates/Science Source; (tr) ©Ed Reschke/Photolibrary/Getty Images; (cr) ©Science Photo Library/Alamy; (b) ©Manfred P. Kage/Science Source; (cl) ©Sebastian Kaulitzki/Alamy

muscle cells in trachea

that can help deliver medicine,
move through the bloodstream
to hard-to-reach areas, and even
destory cancer cells. Research a
type of nanobot currently under
development. How did the purpose
of the nanobot affect its design?
List some structural features
the design has or could have to
complete its purpose.

neurons red blood

cells

sperm cells

The specialization enabled by differentiation is what allows different types of cells to

have different functions. For example, sperm cells have a long tail called a flagellum
that allows for movement. Some epithelial cells in the trachea have hair-like extensions
called cilia. These structures provide a sweeping motion that helps clear small particles
out of the trachea. Neurons have extensions that allow the cell to communicate with
many other cells. This allows for the formation of complex, interconnected networks of
neurons, such as those in the human brain. Your brain contains billions of neurons with
trillions of connections. This allows for communication between the cells of your body,
as well as higher functions such as memory and learning.

Language Arts Connection Red blood cells carry oxygen and nutrients to cells.
To carry out their function, these cells must bind oxygen and travel through small blood
vessels in the circulatory system called capillaries. Capillaries are so narrow that red
blood cells must move through them “single file.” Write an explanation for how the
structure of red blood cells allows them to carry out their function.

Lesson 2 Organisms: Cells to Body Systems 21

 FIGURE 7: The nervous system Neurons
is made up of the brain, spinal
cord, and nerves. The nervous system is a network of nerves and sensory organs that work together to
process information and respond to the environment. The basic unit of the nervous
system is the neuron. Neurons are specialized cells that are able to send electrical and
chemical signals to help the organism sense information, coordinate a response, and
carry out that response.
Humans and other organisms have three types of neurons: sensory neurons,
interneurons, and motor neurons. Sensory neurons detect stimuli and send signals to
the brain and the spinal cord. Interneurons in the brain and spinal cord receive and
process the information from the sensory neurons and send response signals to motor
neurons. Motor neurons act on the signal by stimulating muscles to contract.

Systems and System Models Draw a flow chart illustrating how the three types
of neurons would interact to help a person pick up an object.

Most neurons have three main parts: the cell body, one or more dendrites, and an
axon, shown in Figure 8. The short, branchlike extensions that extend from the cell
body are called dendrites. Dendrites receive electrochemical messages from other
cells. The axon is a long extension of the cell that carries electrochemical signals away
from the cell body and passes them to other cells. The branched endings of the axon
are specialized to transmit electrochemical signals to other cells.

FIGURE 8: The neuron is a specialized cell within the nervous system.

axon

cell body

myelin sheath
axon terminals

dendrites

Just as most electric wires are wrapped in an insulating material, many axons are
wrapped in a protective covering called a myelin sheath. This covering is formed from
a collection of cells that are wrapped around the axon. The myelin sheath protects the
axon and helps speed transmission of nerve impulses.

Analyze Diseases such as multiple sclerosis cause the myelin sheath to break down.
How would the breakdown of myelin affect the functioning of a neuron?

The nervous system interacts with all the other systems in the body. For example,
when you eat, your brain signals your digestive system to start making chemicals and
churning your food. Neurons also stimulate muscle tissue in the digestive system to
contract, which helps the digestive system move and break down food.

22 Unit 1 Living Systems

Muscle Cells FIGURE 9: Skeletal Muscles

Muscles consist of bundles of muscle cells that contract when they are stimulated by
the nervous system. A contraction shortens the muscle, causing the bone or tissue to
which the muscle is attached to move. Some muscles, such as those in Figure 9, are
under voluntary control, so you can choose to move this type of muscle tissue. This
type of muscle is called skeletal muscle. Some muscles are under involuntary control,
meaning they move in response to nerve signals or hormones, but you do not choose
to move them. Smooth muscle in internal organs and cardiac muscle in the heart are
under involuntary control.

Collaborate With a partner, describe an activity that would require muscles that
are under voluntary control and another activity that would require muscles that are
under involuntary control.

The specialized structure of muscle cells allows them to contract. Skeletal muscles
are made up of long cylindrical bundles that contain muscle fibers. Muscle fibers
are bundles of single, thin muscle cells called myofibrils. Each myofibril is made
up of several sarcomeres. A sarcomere is the contractile unit of the muscle cell.
Sarcomeres contain thin filaments made of actin and thick filaments made of myosin.
When a muscle cell is relaxed, actin and myosin are not connected to each other. In
contraction, the myosin attaches to the actin and pulls the actin toward the center of
the sarcomere. This in turn shortens the sarcomere, and the muscle cell contracts. The
contraction of many muscle cells at once shortens the entire muscle.

FIGURE 10: Actin and myosin work together to help a muscle Explore Online
move. During contraction, myosin filaments pull actin filaments toward the center
of the sarcomere.

relaxation Explain How does the

structure of the muscle cell
actin myosin
help it carry out its function?

contraction
muscle

sarcomere

myofibril muscle fiber

Model Construct a model to illustrate how the nervous and digestive systems might
interact to produce the sensation of “butterflies in your stomach.” Which organs are most
likely involved, and how do they interact when you have this feeling?

Lesson 2 Organisms: Cells to Body Systems 23

 EXPLORATION 2

The Cell System

Gather Evidence The most basic level of organization in living things is the cell. Organisms may be
Make a table to record the made up of just one cell, or they may be multicellular. Cells in multicellular organisms
name of each organelle or cell are specialized to perform different functions. Your body is made of trillions of cells
structure, its role in the cell system, of many different shapes, sizes, and functions, including long, thin, nerve cells that
and a simple visual or analogy transmit information as well as short, blocky, skin cells that cover and protect the body.
Despite this variety, the cells in your body share many characteristics with one another
representing that organelle. As
and with the cells that make up other organisms.
you read each section, complete
the table.
Cell Structure
All cells are enclosed by a cell membrane that controls the movement of materials into
and out of the cell. Inside the membrane, a cell is filled with cytoplasm. Cytoplasm is
a jelly-like substance that contains dissolved materials such as proteins and sugars.
These building blocks are used to make cell structures and can be broken down to
release energy used by the cell to do work. Some types of cells also have organelles,
which are specialized structures that perform distinct processes within a cell. Most
organelles are surrounded by a membrane. In many cells, the largest and most visible
organelle is the nucleus, which stores genetic information.
Analyze What is the FIGURE 11: Basic Cell Structure
boundary that separates
the cell system from the
surrounding environment? Explain cell membrane
the function of this boundary.
cytoplasm

nucleus

Image Credits: (l) ©Dr. Kari Lounatmaa/Photo Researchers, Inc.; (r) ©LSHTM/Photo Researchers, Inc.
a b

Prokaryotic and Eukaryotic Cells

Scientists classify cells into two broad categories based on their internal structures:
prokaryotic cells and eukaryotic cells. Prokaryotic cells do not have a nucleus or
other membrane-bound organelles. Instead, the cell’s DNA is suspended in the
cytoplasm. Most prokaryotes are microscopic, single-celled organisms. Eukaryotic
cells have a nucleus and other membrane-bound organelles. Eukaryotes may be
multicellular or single-celled organisms.

Explain Which of the cells in Figure 11 is a prokaryotic cell, and which is a eukaryotic
cell? Cite evidence to support your claim.

24 Unit 1 Living Systems

 Animal Cell Structure
Like your body, eukaryotic cells are highly organized structures. They are surrounded
by a protective membrane that receives messages from other cells. They have
membrane-bound organelles that perform specific cellular processes, divide certain
molecules into compartments, and help regulate the timing of key events.

FIGURE 12: Organelles in the animal cell interact to help the cell carry out functions.

nucleus rough
endoplasmic
reticulum
ribosome cytoskeleton
Analyze Describe how the
endoplasmic reticulum,
lysosome smooth mitochondrion, and Golgi apparatus
endoplasmic are structurally similar.
reticulum
vacuole

mitochondria Golgi apparatus

cytoplasm
cell membrane
vesicle

The cell is not a random jumble of suspended organelles and molecules. Rather,
certain organelles and molecules are anchored to specific sites, depending on the cell
type. If the membrane were removed from the cell, the contents would not collapse
and ooze out in a puddle. The cytoskeleton gives a cell its shape while at the same time
maintaining its flexibility. It is made of small subunits that form long threads, or fibers,
that crisscross the entire cell.
Cytoplasm is itself an important contributor to cell structure. In eukaryotes, it fills the
space between the nucleus and the cell membrane. The fluid portion, excluding the
organelles, consists mostly of water. Water helps maintain the structure of the cell and
provides a medium in which chemical reactions can occur.

Nucleus
The nucleus is the storehouse for most of the genetic information, or DNA, in your
FIGURE 13: The nucleus has
Image Credits: (b) ©DR ELENA KISELEVA/Science Source

cells. DNA is like a blueprint with instructions for making proteins, which carry out
openings called pores.
most of the work in the cell. DNA must be carefully protected, but DNA also must be
available for use at the proper times. Molecules that would damage DNA need to be
kept out of the nucleus. But many molecules are involved in making proteins from
the DNA code, and they need to access the DNA at certain times. The membrane,
or nuclear envelope, that surrounds the nucleus has pores that allow only certain
molecules to pass between the nucleus and cytoplasm.
pores
Structure and Function What purpose is served by controlled openings in the
nuclear membrane?

Lesson 2 Organisms: Cells to Body Systems 25

 FIGURE 14: Rough ER is
Endoplasmic Reticulum and Ribosomes
so named because it has A large part of the cytoplasm of most eukaryotic cells is filled by the endoplasmic
ribosomes on the surface. reticulum. The endoplasmic reticulum, or ER, is an interconnected network of thin,
endoplasmic reticulum
folded membranes. Numerous processes, including the production of proteins, occur
both on the surface of the ER and inside the ER. In some regions, the ER is studded with
ribosomes, tiny organelles that help make proteins.
Surfaces of the ER that are covered with ribosomes are called rough ER, because they
look bumpy when viewed with an electron microscope. Not all ribosomes are bound
to the ER; some are suspended in the cytoplasm. In general, proteins made on the ER
ribosomes are either incorporated into the cell membrane or secreted. In contrast, proteins made
on suspended ribosomes are typically used in chemical reactions occurring within
the cytoplasm. ER that does not have ribosomes on the surface is called smooth ER.
Smooth ER performs a variety of specialized functions, such as breaking down drugs
and alcohol.

Explain Neurons have special proteins in their cell membranes that allow them to
generate electrical current. Are these proteins most likely produced by ribosomes on
the rough ER or ribosomes suspended in the cytoplasm? Explain your answer.

FIGURE 15: The Golgi apparatus Golgi Apparatus

processes and delivers proteins. After a protein has been made, part of the ER pinches off to form a vesicle surrounding
the protein. Protected by the vesicle, the protein can be safely transported to the Golgi

Image Credits: (t) ©MedImage/Photo Researchers, Inc.; (c) ©SPL/Science Source/Photo Researchers, Inc.; (b) ©Bill Longcore/Photo Researchers, Inc.
apparatus. The Golgi apparatus consists of stacks of membrane-enclosed spaces that
process, sort, and deliver proteins. Its membranes contain structures called enzymes
that make additional changes to proteins. The Golgi apparatus also packages proteins.
Some of the packaged proteins are stored within the Golgi apparatus for later use.
Some are transported to other organelles within the cell. Still others are carried to the
membrane and secreted outside the cell.

Collaborate Discuss this question with a partner: If the cell were compared to a
nonliving system, such as a warehouse that ships products to customers, what would
be an appropriate analogy for the Golgi apparatus?

Mitochondria
FIGURE 16: Mitochondria Mitochondria supply energy to the cell. Mitochondria are bean shaped and have a
provide energy to the cell. double membrane, similar to nuclei. Within the inner membrane, a series of chemical
reactions converts molecules from the food you eat into usable energy. Unlike most
organelles, mitochondria have their own ribosomes and DNA. This fact suggests that
mitochondria were originally free-living prokaryotes that were taken in by larger cells.

Predict Which would you predict would have more mitochondria–a muscle cell or a
skin cell? Explain your answer.

Other structures in the animal cell include lysosomes and centrioles. Lysosomes are
membrane-bound organelles that contain special proteins called enzymes. These
enzymes break down and recycle old, worn-out cell parts. Centrioles are involved in
cell division, and they will be discussed in further detail in another lesson.

26 Unit 1 Living Systems

 Plant Cell Structure
Plant cells have many of the same organelles as animal cells, but they also have some Explore Online
distinct differences. Two important differences are structures that enable plant cells to
Hands-On Lab
capture light energy from the sun and to have a more rigid support structure.
Comparing Cells Use a
FIGURE 17: Plant cells have specialized structures that carry out specific functions, such microscope to investigate the
as protecting the cell and capturing energy.
similarities and differences
between plant and animal cells.
Golgi apparatus nucleus
rough
endoplasmic
vesicle reticulum
central
vacuole
cytoskeleton

chloroplast ribosome

smooth
endoplasmic
vacuole reticulum

mitochondria

cell wall
cell membrane

Explain What organelles do plant cells have that animal cells do not have? What do
you think is the function of each of these organelles?

Cell Wall FIGURE 18: The cell wall

Plants, algae, fungi, and most bacteria have a cell wall that surrounds the cell provides protection and
membrane. The cell wall is a rigid layer that gives protection, support, and shape to the support for the cell.
cell. The cell walls of multiple cells can adhere to each other to help support an entire
Image Credits: (b) ©Ed Reschke/Peter Arnold/Getty Images

cell wall
organism. For instance, much of the wood in a tree trunk consists of dead cells whose
cell walls continue to support the entire tree.

Analyze The cell walls of plant cells have openings, or channels. How is this
structure most likely related to the proper functioning of the plant system?

Lesson 2 Organisms: Cells to Body Systems 27

 FIGURE 19: Chloroplasts carry
Chloroplast
out photosynthesis. Chloroplasts are organelles that carry out photosynthesis, a series of complex chemical
reactions that convert light energy from the sun into energy-rich molecules the cell
can use. Like mitochondria, chloroplasts are highly compartmentalized. They have
both an outer membrane and an inner membrane. Also like mitochondria, chloroplasts
have their own ribosomes and DNA. Scientists have hypothesized that they, too, were
originally free-living prokaryotes that were taken in by larger cells.

Collaborate Where do you think the most chloroplasts are found in the plant
system–in leaves, the stem, or the root? Use evidence to support your answer.

Vacuole
A vacuole is a fluid-filled sac used for the storage of materials needed by a cell. These
FIGURE 20: The vacuole stores materials may include water, nutrients, and salts. Most animal cells have many small
materials needed by the cell. vacuoles. The central vacuole, shown in Figure 20, is a structure unique to plant cells.
It is filled with a watery fluid that strengthens the cell and helps to support the entire
plant. The central vacuole also may contain other substances, including toxins that
would harm predators, waste products that would harm the cell itself, and pigments
that give color to cells, such as those in the petal of a flower.
vacuole

Analyze When a plant wilts, its leaves shrivel. How is this phenomenon related to

Image Credits: (t) ©Biophoto Associates/Colorization by Mary Martin/Science Source; (b) ©Biophoto Associates/Colorization by Jessica Wilson/Science Source
the function of the vacuole in the plant system?

Explaining the Cell System Boundary

The cell membrane is an important structure for cell function. The cell membrane,
or plasma membrane, forms a boundary that separates the organelles within the
cell from the environment outside of the cell. The cell membrane also controls the
Predict How do you passage of materials into and out of a cell. The complex, double-layer structure of
think the structure of the the membrane makes it possible for the cell to selectively pass materials, such as
cell membrane allows for some nutrients, water, and waste, in and out of the cell. In this way, the cell membrane
materials to move into the cell, maintains stable conditions within the cell, even when conditions in the surrounding
while other materials are kept out? environment change.
In addition, the structure of the cell membrane allows the cell to communicate with
other cells. For example, a neuron has specialized structures in its cell membrane that
help it send and receive chemical and electrical signals. The membrane’s structure
helps the cell carry out its function within the nervous system, and the nervous
system helps the organism interpret information from their environment and
respond accordingly.

Explain Make a claim for how the organization in eukaryotic cells allows these cells
to perform specialized functions within an organism. How do the components of the cell
system interact to help it carry out specific tasks and interact with other systems in the
body? Use evidence and examples to support your claim.

28 Unit 1 Living Systems

 CONTINUE YOUR EXPLORATION

Engineering

Modeling Interacting Body Systems

In this lesson, you have learned about body systems and Conduct Research
how they interact in organisms. Now it is your turn to model
Research to learn more about how the body systems
interacting body systems within an organism. In this activity,
interact to carry out the task that you chose. As you search
you will create a model to show how systems within an
for information, keep track of your sources to submit with
organism interact to carry out a task of your choice.
your final model. Be sure to use sources that are reliable. For
FIGURE 21: Body systems interact to help keep you healthy. example, government and educational institutions are more
reliable than personal websites. With your final model, submit a
list of resources in the format specified by your teacher.

Make a Model
Your model should include text and media that illustrate how
systems interact at different levels to help an organism carry
out a task. Consider the levels of organization involved, such
as cells, tissues, organs, and organ systems. The model should
also demonstrate how energy, materials, and information flow
within and between systems in the organism.

Language Arts Connection Present your model to

Define the Systems
your peers. Explain how it illustrates interactions between
Decide on a task that interests you, such as running, playing systems required to carry out the task you chose. Consider
video games, or talking to a friend. Think about the body using illustrations, simulations, or demonstrations to
systems that are likely involved in completing that task. For explain the processes involved clearly.
example, the man in Figure 21 is drinking water to rehydrate
after being in the sun. His integumentary system, or skin, A multimedia presentation combines text, sounds, and
sweats to keep him from overheating. As he loses water images. A successful multimedia presentation includes:
through sweat, his nervous system processes information • a clear and consistent focus;
from the body and sends signals that make the man feel
thirsty. To quench his thirst, the man drinks water, which
• ideas that are presented clearly and logically;
eventually reaches his digestive system. Water passes • graphics, text, music, video, and sounds that support key
across cell membranes and eventually into his blood, which points; and
transports it to his cells. • an organization that is appropriate to its purpose and
Image Credits: ©Dennis Walsh/UpperCut Images/Getty Images

audience.
Select an Appropriate Model
Select the type of model you would like to use to illustrate the
interactions among your systems. Types of models include
conceptual models, physical models, mathematical models, and
computer models. Your model should use media and materials
effectively. It should show that you understand the concepts
that you are illustrating and capture the audience’s interest.

COMPARING PROKARYOTES Go online to choose one of

PLANT TISSUES AND CELLS
AND EUKARYOTES these other paths.

Lesson 2 Organisms: Cells to Body Systems 29

 EVALUATE

Lesson Self-Check

CAN YOU EXPLAIN IT?

FIGURE 22: A ballerina awaits her cue backstage.

Recent research has shown that the nervous system and digestive system are very
closely connected. Nerves not only send signals to the digestive system to function
when needed, but the digestive system sends signals to the nervous system. In fact,
scientists refer to the portion of the nervous system associated with the gut as our
“second brain,” because it can operate without any input from the brain to continue
the digestive process. The second brain contains around 100 million neurons, more
than the spinal cord or the peripheral nervous system. Thus, part of our emotions may
be tied to the nerves in our digestive system.

Explain Use your model of the nervous and digestive systems and the evidence you
have gathered in your Evidence Notebook to construct an explanation of how
sensations, such as “butterflies” in the stomach, might arise. Which organs do you
think are communicating, how are they communicating, and what is the function of Image Credits: ©MUJAHID SAFODIEN/AFP PHOTO/Getty Images
this communication?
1. State your claim.
2. Summarize the evidence you have gathered to support your claim, and explain
your reasoning.
3. Use your model to illustrate your claim. Revise the model as needed based on new
evidence you gathered.

30 Unit 1 Living Systems

EVALUATE

CHECKPOINTS

Check Your Understanding

FIGURE 23: Organs such as the stomach are made up of four
main types of tissues.
1. Which of the following correctly describes the
relationship between tissues and organs? epithelial tissue
epithelial
a. Several organs interact to help a tissue carry out a provides protective
tissue
lining; allows for
transport, secretion,
specialized function. and absorption

b. One type of specialized tissue is found in each organ.

connective tissue
c. Organs are made up of different types of tissue that connective
supports, binds
together, and
work together. tissue
protects other
tissues and organs
d. Tissues compete with each other to carry out the main
function of the organ. muscle tissue
muscle
contracts to allow
for movement,
tissue
support, and
2. Which of the following organ systems must work heat production

together to bring oxygen to the body’s cells? Select all

nervous tissue
correct answers. nervous
receives and
transmits impulses;
a. digestive system tissue
processes
information

b. skeletal system
c. immune system
d. respiratory system 8. How do the four types of tissue shown in Figure 23
interact to help the stomach carry out its function of
e. circulatory system
breaking down food?

3. The word organ comes from the Latin word organum,

meaning “instrument” or “implement.” Describe how this
MAKE YOUR OWN STUDY GUIDE
meaning relates to the definition of a living organ.

4. Draw a diagram to show the relationship between cells, In your Evidence Notebook, design a study guide that
organs, tissues, organ systems, and organisms. Include supports the main idea from this lesson:
media and text in your diagram.
Systems in organisms interact at different levels to carry out
functions necessary for life.
5. Explain how the structure of a plant cell helps the plant
system maintain its shape. Remember to include the following information in your
study guide:
6. Which organelles are found in plant cells but not animal • Use examples that model main ideas.
cells? How are these structures related to functions at the • Record explanations for the phenomena you investigated.
organism level? • Use evidence to support your explanations. Your support can
include drawings, data, graphs, laboratory conclusions, and
7. List the main organ systems that would interact to help a other evidence recorded throughout the lesson.
person play the violin, and explain how they would work
together to help the person complete this task. Consider how the information in this lesson can help you model
interactions within and between systems at different levels.

Lesson 2 Organisms: Cells to Body Systems 31

 1.3

Mechanisms of Homeostasis

Your circulatory system

responds to an increase CAN YOU EXPLAIN IT?
in cellular metabolism
by increasing the flow of
The complex tissues, organs, and organ systems in your body must respond to a
oxygen-carrying red blood
cells to your tissues. wide variety of conditions. For example, you might walk out of a warm building
into the cold outside and feel the drastic change of temperature. Your body
temperature must remain the same in both conditions for you to survive.

FIGURE 1: Your body has control systems that keep its internal environment stable.
Gather Evidence
As you explore this lesson,
gather evidence about the ways
your body responds to changing
environmental conditions.

Image Credits: (t) ©Science Picture Co./Science Source; (b) ©Hero Images/Alamy

When it is cold outside, you likely wear warm clothing and you might drink a hot
beverage to stay warm. However, if you become too cold, your body’s temperature
control center jumps into action. Receptors in your skin send signals to the brain,
which sets into motion warming tactics, such as shivering. When you shiver, your
muscles contract and expand in quick bursts, which releases energy and helps you
to warm back up.

Predict Many people shiver when they have a fever, even though their body
temperature is higher than normal. Why would your body respond to the increased
internal temperature as though you were cold?

32 Unit 1 Living Systems

EXPLORATION 1

Control Systems in Organisms

External and internal factors such as temperature changes, infection, stress, and
pollution challenge the stability of an organism. In the same way that a cell must
maintain stable conditions, an organism must maintain stability despite changes
in its internal state or within the environment in which it lives.

Control Systems
Fortunately, the body has many control systems that keep its internal environment
stable. Together, these control systems are responsible for maintaining homeostasis.
Homeostasis is the regulation and maintenance of the internal environment within the
narrow ranges that are necessary to support life at the cellular level.

FIGURE 2: Control systems maintain homeostasis.

Control
3 4
Center

Receptor Effector

5
Imb
alan
ce
2

Balance

Imb
alan
ce

As shown in Figure 2, homeostasis is maintained through the following steps:

1. A stimulus is anything from the internal or external environment that causes an
imbalance in the internal conditions of a cell, organ, organ system, or organism.
Gather Evidence
2. Stimuli are detected by receptors. There are thousands of internal receptors, as well
Identify a change in your
as specialized receptors that detect information about changes in the organism’s
environment that might affect
external environment.
homeostasis. Explain using the
3. The receptor sends information to a control center, often in the central nervous
terms stimulus, control center, set
system. The control center compares the information to set points. Set points are
point, receptors, effectors, and
ideal values for the conditions at which the body functions best.
imbalance in your answer.
4. If the control center detects movement away from the set point, it responds
by sending messages through one of the organism’s communication systems.
Messages sent by the control center are carried to effectors that carry out the
response.
5. The response restores balance by returning internal conditions to their set points.

Lesson 3 Mechanisms of Homeostasis 33

 Homeostasis depends on communication between the receptors, the control center,
and the effectors. In the human body, communication is the joint responsibility of the
nervous system and the endocrine system.
The nervous system sends messages along a direct route between the receptor and
Model Use the
the control center, or between the control center and the effector. The control center
homeostatic control
in the human body is the central nervous system, which consists of the brain and the
systems diagram in Figure 2 to spinal cord. Some responses, such as shivering, are generated by the spinal cord and
explain how shivering can help are called reflex responses. Information that requires more interpretation, such as
body temperature return to normal. visual and auditory input, is routed through the brain.
Unlike the nervous system, the endocrine system uses a more indirect—but still
rapid—method of communication. Hormones are chemicals secreted into the
bloodstream by ductless endocrine glands. The hormones then travel throughout the
body, acting only on cells that have receptors for those particular hormones.

In order to maintain homeostasis, receptors throughout the organism must constantly

compare current conditions to the appropriate set points. Set points are actually
narrow ranges of acceptable conditions in a cell or organism. If receptors detect a
change in an internal condition causing it to stray outside the set point, the control
center communicates instructions to the effector. The effector acts to restore the
internal environment to its set point. This interaction between the receptor, the
control center, and the effector is known as a feedback loop.

Hands-On Activity

Modeling Feedback

Have you ever lost and recovered your balance? If so, you’ve experienced a
FIGURE 3: Feedback will
feedback loop between your center of balance and your skeletal muscles. In this
help you balance a book
activity, you will balance a book on your head while walking.
on your head.
Predict How would you need to adjust your balance to keep a book balanced
on your head?

PROCEDURE
1. Balance the hardcover book on your head.
2. Walk 3 meters forward and backward—once with your eyes open,
then with your eyes closed.
MATERIALS 3. Always walk with a partner when your eyes are closed and clear any objects
• Hardcover book, from your path.
at least 6" × 8"
Image Credits: ©Rob Lewine/Getty Images

ANALYZE
1. What type of receptors provided information about the position of the book
while you walked?
2. How did you respond whenever the book changed position? Did you find
it more or less difficult to maintain balance with your eyes closed? Explain
your answer.

34 Unit 1 Living Systems

Negative Feedback Loops

Consider what happened in the book-balancing activity. You responded to a change

in the book’s position by changing your speed or moving your body in the opposite
direction until the book returned to balance. You continued to make adjustments to
maintain that balance until you removed the book from your head.

What you experienced was the result of a negative feedback loop. In a negative
feedback loop, a stimulus causes an imbalance in one direction. This imbalance is
detected by receptors that send information to the control center. The control center
evaluates the information and sends a signal to the effectors to make an adjustment
that is in the opposite direction from the stimulus, returning the system to balance.

Why is this process called a loop? The receptors also check the new conditions that
result from the actions of the effector and then update the control center. The control
center then signals any additional actions that the effector needs to take. These small
changes cause conditions to hover around the set point and maintain homeostasis.

FIGURE 4: Negative Feedback Loop Flow Chart

Stimulus causes Receptor monitors

deviation from set point. conditions.

Control center compares

information from receptors Imbalance is conteracted.
to set point.

Effector carries out response

Body is at homeostasis. NO Is there an imbalance? YES
from control center.

The thermostat of a furnace is a nonliving example of a negative feedback loop. The

thermostat contains a receptor (thermometer), a control center (microprocessor),
and an effector (switch). The set point is the programmed temperature. When the
thermometer detects that the air temperature is lower than the set point, it signals the
thermostat’s microprocessor, which responds by turning on the switch of the furnace. Analyze Based on
Figure 4, explain how the
While the heating system is running, the thermometer continues to measure air body uses a negative feedback loop
temperature and send updates to the microprocessor, which compares it to the
to regulate body temperature. Use
desired temperature. Once the air temperature reaches the set point or just slightly
the terms control center, stimulus,
above it, the control center turns off the furnace until the room temperature once
set point, receptors, effectors, and
again drops below the set point. As a result, the room temperature remains within a
couple of degrees of the set point. imbalance in your answer.

Your body has its own internal thermostat. Humans need to maintain a body
temperature between 36.7 °C and 37.1 °C (98.2 °F and 98.8 °F). This narrow range is
maintained by several mechanisms. Two of these mechanisms are sweating to cool
down when the temperature exceeds 37.1 °C and shivering to warm up when it drops
below 36.7 °C.

Lesson 3 Mechanisms of Homeostasis 35

 Positive Feedback Loops
Just as there are negative feedback loops in living systems, there are also positive
feedback loops. A negative feedback loop makes adjustments in the opposite direction
of a stimulus, but a positive feedback loop makes adjustments in the same direction
as the stimulus. Scientists sometimes refer to positive feedback loops as reinforcing
loops, because they amplify the stimulus instead of counteracting it.
Have you ever experienced a loud screech coming from a loudspeaker in an
auditorium or at a show? This is an example of a positive feedback loop. The sound
from the microphone is amplified and sent through the loudspeaker. Sometimes, the
microphone will pick up that sound again, it is amplified, and sent through the speaker
again. This loop continues again and again. Eventually, you hear the high-pitched
screech from the loudspeaker.

FIGURE 5: Positive Feedback Loop Flow Chart

Stimulus causes Receptor monitors

deviation from set point. conditions.
YES Is the task complete? NO

Control center compares

information from receptors Imbalance is conteracted.
to set point.

Effector carries out response

Body is at homeostasis. NO Is there an imbalance? YES
from control center.

Collaborate Oxytocin is Positive feedback is important when rapid change is needed, such as when you cut
a pituitary hormone that your finger. Your body depends on maintaining blood volume and blood pressure. A
stimulates the muscles in the uterus cut results in blood loss, so the body depends on a positive feedback loop to quickly
generate a clot to stop the bleeding. This occurs as platelets and clotting factors
to contract during birth. It also
stimulate the activation of more platelets and clotting factors at the wound. Once the
stimulates the release of
cut has healed, a clot is no longer needed (and could be dangerous if it gets into the
prostaglandins from the placenta,
bloodstream). The body then uses another positive feedback loop to dissolve the clot.
causing more uterine contractions.
With a partner, explain how this Positive feedback loops are not as common in the body as negative feedback loops,
process is a positive feedback loop. but they are important for maintaining homeostasis. For example, some hormones
are regulated by positive feedback loops. The release of one hormone may stimulate
the release or production of other hormones or substances, which stimulate further
release of the initial hormone.

Explain The body relies on positive and negative feedback loops to maintain
homeostasis. One such feedback loop is used to maintain water balance in the body. What
type of feedback loop returns the body to homeostasis when it becomes dehydrated? Use
evidence from this lesson to support your answer.

36 Unit 1 Living Systems

 EXPLORATION 2

Homeostasis in the Human Body

Homeostasis regulates many different things in organisms, such as temperature, Explore Online
water balance, salt levels, pH, nutrients, and gases. Because all of these things have
Hands-On Lab
set points, the body requires feedback loops for each one in order to maintain
homeostasis. Remember that at its most basic level, the body is composed of many Negative and Positive Feedback
groups of specialized cells. These cells are further organized into organs, which in Analyze data and generate graphs
turn are organized into systems. Whatever affects one organ system affects the body to determine whether a process is
as a whole. This means that whenever an imbalance occurs in one organ system, the an example of a negative or positive
imbalance affects the entire organism.
feedback loop.

Interacting Organ Systems

All of your body systems interact to maintain homeostasis, much like a group of
dancers interact to perform a highly choreographed ballet. If one dancer misses a
cue, it throws the rest of the dancers out of step and time. Consider the importance
of a healthy blood pressure to the body. Blood pressure is the force with which blood
pushes against the walls of blood vessels. Receptors in the blood vessels and heart
detect changes in blood pressure, then signal the brain. The brain stimulates the heart
to beat faster or slower to help restore the blood pressure to its correct level.
Arteries are a type of blood vessel in the circulatory system that carry oxygen-rich
blood throughout the body. If blood pressure is too low, the brain tells the heart
to beat faster to increase the amount of blood in the arteries, which increases the
pressure exerted by the blood on the walls of the arteries. If the pressure is too high,
the heart beats slower, reducing the amount of blood in the arteries and so lowering
the blood pressure. In this case, the systems working together to maintain blood
pressure homeostasis are the nervous system and the circulatory system.

Cause and Effect

Blood pressure depends on how elastic and unblocked the arteries are and on
FIGURE 6: Blocked Artery
the strength of the heart contraction. The less elastic the arteries and the more
blockages that reduce blood flow, the harder the heart must pump. As a result,
blood pressure rises. Blood pressure also rises naturally with activity, stress, and
strong emotions, but it should drop again with rest. If the pressure remains high,
Image Credits: ©Colorization by: Mary Martin/Science Source

there could be a problem in the circulatory system.

Predict If a person’s blood pressure is too high or too low, how might the other
organ systems in their body be affected?

Lesson 3 Mechanisms of Homeostasis 37

 Maintaining Glucose Concentrations
The cells in the human body rely heavily on glucose to supply the energy needed to
survive and grow. However, glucose concentrations in the blood must be maintained
within a very narrow range for good health. Glucose needs can vary widely depending
on what activities the body is performing. A person’s activity levels are always
changing, so the body must work constantly to maintain homeostasis.

FIGURE 7: Glucose levels are regulated by a negative feedback loop.

Receptors Blood glucose Blood glucose Receptors

detect change level drops level rises detect change

Pancreas releases Pancreas releases

glucagon Homeostasis insulin

Body cells take

up glucose
Liver breaks down Blood glucose Blood glucose
glycogen and level rises level drops
Liver stores glucose
releases glucose
as glycogen

Blood glucose levels are controlled by two feedback loops, shown in Figure 7. Each
loop relies on the endocrine system to respond to changing levels. When blood
glucose levels rise, such as when you eat a meal, the increase is detected by beta cells
in the pancreas. The beta cells respond by releasing insulin, which stimulates cells to
absorb glucose from the blood stream. It also causes the liver to store excess glucose
in the form of glycogen. Once levels return to the set point, insulin secretion subsides.
This feedback keeps blood glucose levels from exceeding the maximum set point.
The body has a second feedback loop that maintains a minimum blood glucose
Analyze Why are the level. Blood glucose levels can drop after a long time passes without eating or during
insulin and glucagon prolonged exercise. When the brain detects levels below the minimum set point, it
signals pancreatic alpha cells to produce glucagon. Glucagon stimulates the liver to
feedback loops examples of
convert glycogen to glucose and release it into the blood stream. If the liver is unable
negative feedback loops?
to release glucose rapidly enough, the brain signals a feeling of hunger in order to
obtain additional glucose.

Explore Online Maintaining Carbon Dioxide Concentrations

Hands-On Lab
Every time you exercise, lie down to rest, or simply stand up, your needs for oxygen
Investigating Homeostasis and nutrients change. Your heart speeds up or slows down and you breathe faster
and Exercise Investigate how or slower, depending on your level of activity. The respiratory system interacts with
the circulatory system, respiratory the nervous system to maintain homeostasis. Control centers in the brain monitor
system, and perspiration levels are dissolved gases in the blood, particularly carbon dioxide (CO2) and oxygen (O2)
affected by exercise. concentrations.

38 Unit 1 Living Systems

As you become more active, CO2 levels increase and the blood becomes more acidic.
FIGURE 8: Circulatory System
Sensors signal this change to the brain. The brain sends messages through the nervous
and endocrine systems that stimulate the diaphragm and rib cage muscles to work
more rapidly. This allows you to take in more O2 and release CO2, returning levels in
your body to homeostasis.
In humans, gas exchange is a cooperative effort of the circulatory and respiratory
systems. The circulatory system distributes blood and other materials throughout the
body, supplying cells with nutrients and oxygen, and carrying away wastes. Blood
vessels are organized so that oxygen-poor blood and oxygen-rich blood do not mix.
The circulatory system has three types of blood vessels: arteries, veins, and capillaries.
Arteries carry oxygen-rich, or oxygenated, blood away from the heart. Veins are blood
vessels that carry oxygen-poor, or deoxygenated, blood back to the heart. Capillaries
are responsible for delivering O2 directly to cells and removing CO2 and waste. With
a wall only one cell thick, it is easy for materials to diffuse easily into and out of
capillaries. The capillary system serves as a connection between arteries and veins,
ensuring a continuous path for blood flow throughout the body.
Once the veins deliver deoxygenated blood to the heart, it is immediately transported
to the lungs, where gases can be exchanged with the air. As shown in Figure 8, when
you inhale, the air flows from your nose or mouth through the trachea to the bronchi
(sing. bronchus). The air continues into smaller branches called bronchioles and finally
into small, thin-walled air sacs called alveoli. A network of capillaries surrounds each
alveolus, taking in O2 and releasing CO2. When you exhale, the CO2 exits through your
nose or mouth.

FIGURE 9: Diffusion of gases into and out of the alveoli maintains oxygen and carbon dioxide homeostasis.

bronchiole alveoli
nose
bronchus capillary
mouth
CO2
trachea
alveolus

O2

alveoli capillaries
lungs

Gas homeostasis in the blood is maintained through diffusion. When you inhale, the Model Create a flow
air has a higher concentration of O2 than the blood in the capillaries surrounding Make a flow chart
the alveoli. This allows O2 to diffuse down a concentration gradient into the blood. explaining how homeostasis is
From there, the blood is taken to the heart and pumped through the body. The maintained when you become more
concentration of O2 in the blood is higher than in the cells, so it diffuses out of the active. How do the respiratory and
blood. Carbon dioxide diffuses in the opposite direction—from the cells into the
nervous systems interact to
blood. The concentration of CO2 is higher in the cells than in the blood because cells
maintain appropriate CO2 and O2
produce CO2 as a waste product. Once in the blood, it travels back to the heart and
levels and prevent the blood from
then into the lungs, where it diffuses into the alveoli and is exhaled out of the lungs.
becoming too acidic?

Lesson 3 Mechanisms of Homeostasis 39

 Disrupting Homeostasis
Homeostatic mechanisms usually work quickly, but sometimes a change in the
environment can occur too rapidly or be of too great a magnitude to be controlled
through feedback mechanisms. When this happens, homeostasis is disrupted.
Disruptions can happen for several reasons including the failure of sensors to detect
a change in the internal or external environment, sending or receiving the wrong
message, serious injury, or disease-causing agents, such as bacteria or viruses.
A rhinovirus, shown in Figure 10, can change the body’s internal chemistry to cause
the common cold. This results in disruption of one or more homeostatic mechanisms.
One commonly disrupted mechanism is body temperature, resulting in fever. A fever
occurs when the hypothalamus raises the set point for internal temperature. This
makes you feel cold, because your internal temperature is below the set point. Your
body may shiver to raise your internal temperature closer to the new set point.

FIGURE 10: The common cold is caused by a rhinovirus.

Short-Term Effects
Collaborate With a Many disruptions in homeostasis are temporary. A cold is an excellent example of a
partner, discuss whether short-term disruption in homeostasis. When the virus first enters your body, it may
multiply too rapidly for your immune system to destroy it. When that happens, you
your body’s response to the
may experience cold symptoms, such as a sore throat or runny nose. In only a few
common cold is an example of
days, however, your immune system develops antibodies that can mark the virus
negative or positive feedback. Use
for destruction, restoring homeostasis. Lasting damage from the common cold is
evidence to support your claim. very rare.
Recall that shivering is the body’s response to decreased body temperature. Shivering
occurs when you are sick not because you are experiencing cold environmental
temperatures, but because your body is trying to adjust to a new—higher—set point
for body temperature. In other words, your body is shivering to produce a fever.

Long-Term Effects
Image Credits: ©James Cavallini/Science Source

Long-term disruptions of homeostasis can cause more damage than short-term

disruptions. One form of long-term disruption is Cushing’s syndrome. This disorder
is caused by a long-term elevation of the hormone cortisol. Cushing’s can result from
tumors of the adrenal or pituitary gland, or from long-term cortisone treatment.
Cortisol is one of the body’s stress hormones. When it remains elevated for long
periods of time, it disrupts glucose and fat metabolism, immune response, and sleep,
and causes blood pressure to increase. Each of these disruptions can lead to other
disorders, such as hypertension, diabetes, strokes, and heart attacks.

40 Unit 1 Living Systems

 Data Analysis

Understanding Diabetes

Recall that the regulation of blood glucose levels occurs through negative feedback
loops. The insulin loop is stimulated by elevated blood glucose levels, and the
glucagon loop is stimulated by lowered blood glucose levels.
Diabetes mellitus is a long-term disruption of the insulin feedback loop. Type 1
occurs when the body’s immune system destroys the ability of beta cells in the
pancreas to produce insulin. Type 2 is caused when pancreatic insulin production
decreases or when insulin cannot move glucose from the blood into cells.

FIGURE 11: Blood glucose, insulin, and glucagon responses to a high-carbohydrate meal.

120 120 120

glucose insulin glucagon
μU/mL

80

pg/mL
110
mg/dL

100
40 100

80 0 90
–60 0 60 120 180 240 –60 0 60 120 180 240 –60 0 60 120 180 240
Minutes Minutes Minutes
High carbohydrate meal High carbohydrate meal High carbohydrate meal

Two variables are inversely related if an increase in the value of one variable is
associated with a decrease in the value of the other variable. For example, the
levels of insulin and glucose increase and glucagon decreases when a person eats.
Therefore, insulin and glucose levels have an inverse relationship to glucagon. This
relationship can be seen in Figure 11.

Analyze Answer the following questions in your Evidence Notebook:

1. What is the relationship between blood glucose levels, insulin levels, and glucagon
levels in the blood stream?
2. Type 1 Diabetes occurs when the body’s immune system destroys the ability of the
pancreas to produce insulin. How would these graphs look different in a person
with Type 1 diabetes?

Homeostasis is critical for the health of any organism and requires various systems to
interact. To maintain some homeostasis some organisms may use methods similar
to those in humans, and others may require different methods specific to their
environment.

Explain Choose an example of a homeostatic variable from this lesson. Explain the
feedback loop responsible for maintaining homeostasis for this variable. Then describe
how homeostasis for this variable can be disrupted.

Lesson 3 Mechanisms of Homeostasis 41

 EXPLORATION 3

Homeostasis in Other Organisms

Many of the homeostatic processes you have learned about in humans are the same
in other organisms as well. However, some organisms use different mechanisms to
maintain homeostasis. For example, not all mammals have sweat glands all over
their skin and so are unable to rely on sweating to cool off. As sweat evaporates, heat
is removed with it, cooling the skin. Dogs make up for the lack of sweat glands by
panting. When they pant, the short, shallow breaths direct air flow over the moist
linings of their upper respiratory tract. This has the same evaporative cooling effect as
a breeze passing over your sweaty skin.

Predict What other organisms do you think would have different homeostasis
mechanisms from humans? Why would this be an advantage in their environment?

Gas Exchange in Plants

Plants take in carbon dioxide for photosynthesis and give off oxygen as a waste
product. In plants, like in humans, homeostatic mechanisms regulate gas exchange.
Gases are exchanged through structures called stomata (singular, stoma). Stomata are
small openings, or pores, on the underside of leaves that are surrounded by cells called
guard cells. Stomata can be open or closed, depending on the needs of the plant.
When the sun is out, certain wavelengths of light are absorbed
FIGURE 12: Stomata help a plant maintain homeostasis.
by a protein called phototropin, stimulating a series of
reactions that causes the guard cells to fill with water. The
guard cells become more rigid, causing the stomata to open.
While the stomata are open for photosynthesis, water vapor is
given off. Giving off water vapor is not necessarily bad for the
plant. In fact, it helps draw water into the plant at the roots. It
also allows the plant to eliminate the oxygen produced during
photosynthesis.
Water vapor loss is not a problem for plants in moist
environments. However, plants in dry or drought
environments may struggle to maintain water balance
because they lose water faster than they can replace it. This
causes the plant to wilt and disrupts other homeostatic
mechanisms that rely on nutrients that are drawn into the
roots with water. To counteract this, many types of plants
Image Credits: ©Power and Syred/Science Source

release a hormone called abscisic acid, or ABA, from the roots

in response to decreased soil water levels. The accumulation
of ABA in leaves triggers the transport of water out of the
guard cells. This causes the cells to relax, closing the stomata.

Analyze Determine the stimulus, receptor, control center response, and effector for
gas exchange for plants.

42 Unit 1 Living Systems

 Stability and Change

Plant Response to Drought FIGURE 13: The root growth of the plant on the right has
been affected by drought.
How does a plant cope with long-term or recurring water
stress? Again, the homeostatic mechanism begins with
the roots. One of the effects of drought is to alter the way
roots grow in various plants. For example, when the plant
maidenstears (Silene vulgaris) experiences moderate drought-
stress, its roots grow deeper into the soil in search of water. A
larger percentage of the roots are thin, allowing them to reach
into tiny pores in the soil in search of every drop of water. In
other plant species, such as myrtle (Myrtus communis), the
percentage of thicker roots is greater in drought conditions.
Scientists also discovered that roots in drought-stressed
maidenstears have more branches than those grown under
normal conditions.
Normal roots are relatively white and flexible. Drought stress
tends to make roots become harder and turn brown. This
is due to the presence of a waxy substance called suberin,
the main component of cork. This forms a protective cap on
the root tip as it enters a resting phase while soil moisture
remains low.
Another change observed in drought-stressed plants is an
increase in the thickness of the root cortex—the outer layer of
root tissue. This helps protect the root from dehydration.

Model Create a model demonstrating how this feedback

mechanism helps a plant maintain homeostasis during a
drought.

Thermoregulation

Not all feedback loops involve nerve impulses or hormones. Thermoregulation Explain
maintains a stable body temperature under a variety of conditions. Sometimes, Is thermoregulation an
the response to a temperature imbalance is a change in behavior. This type of example of negative or positive
feedback response is how cold-blooded animals, or ectotherms, manage their feedback? Use evidence to support
Image Credits: ©marinagluxova 30/Fotolia

body temperature. Unlike warm-blooded animals, or endotherms, that use your answer.
metabolic processes to manage internal body temperature, ectotherms do not have
physiological mechanisms to maintain a constant body temperature. Instead, their
body temperature is determined by their surrounding environment. When ectotherms
become too cold, they move to a warmer environment. When they become too hot,
they move to a cooler environment. This behavior helps them maintain homeostasis.

Lesson 3 Mechanisms of Homeostasis 43

 Osmoregulation
When you live in a watery environment, you must have a strategy to maintain water
and salt balances. If you live in salt water, your environment is constantly trying to
dehydrate you. If you live in fresh water, your body acts like a permanently thirsty
sponge. Saltwater and freshwater fish have developed strategies to cope with
these problems. As part of those prevention strategies, both types of fish undergo a
homeostatic process called osmoregulation, which balances fluid and salt levels.

FIGURE 14: The type of water environment determines the osmoregulation strategy of fish.

Water and salt Water and some Water and salt

obtained through gills salt gained in food excreted through gills

Small amounts of salt and Large amounts of salt and Water and salt gained
large amounts of water small amounts of water through food and
excreted by kidneys excreted by kidneys drinking seawater
a Freshwater fish b Saltwater (marine) fish

Fish in freshwater environments (Figure 14a) must retain as much salt as possible in
Collaborate order to maintain osmotic balance. Their kidneys reabsorb salt and excrete very dilute
urine to rid themselves of as much excess water as they can. At the same time, they
A saltwater fish swims into
take in salt through the gills and in food, and drink very little water.
a river delta, where the salt
concentration is lower than in In contrast, when marine fish ingest salt water (Figure 14b), their bodies attempt to
normal saltwater. This would excrete, or get rid of, as much of the salt as possible in order to maintain osmotic
disrupt its osmotic balance. With a balance. The kidneys help extract salt from the body and concentrate it into very salty
partner, explain how the fish’s body urine, which is then excreted from the body. The fish’s gills actively excrete salt as well.
will restore homeostasis. Land animals, on the other hand, must maintain osmotic balance in a dry environment.
Their primary goal for osmotic regulation is water conservation. The kidneys of
land animals work more like those of a saltwater fish. That is, the necessary water

Image Credits: (l) ©Life on White/Alamy Images; (r) ©Martin Harvey/Alamy

is reabsorbed and excess salt ions are excreted. The drier the climate and the more
difficult it is to obtain water, the more concentrated the urine will be.
The type of nitrogenous waste that land animals excrete also affects their ability to
maintain osmotic balance. Fish excrete this waste as urea, which is water-soluble. Most
mammals also excrete urea. This means they must take in enough water to maintain
osmotic balance while excreting enough to flush the urea from their bodies. Reptiles,
amphibians, birds, and insects excrete these wastes as insoluble uric acid. This allows
them to conserve water by producing highly concentrated urine.

Explain Make a flow chart modeling a homeostatic mechanism in an animal and how it
can be disrupted. In your flow chart, note the stimulus, receptor, control center response,
and effector for the feedback loop.

44 Unit 1 Living Systems

 CONTINUE YOUR EXPLORATION

Hands-On Lab

Investigating Homeostasis and Exercise

Your body’s temperature, heart rate, and blood pressure need to remain within
FIGURE 15: Increased activity
certain set ranges. An increase in activity level will shift these values, and your
can affect homeostasis.
body will use feedback loops to bring levels back to the target set points. Exercise
particularly affects the circulatory and respiratory systems as well as perspiration
levels. In this lab, you will develop an experiment to test the effect of exercise on
homeostasis and then create graphs to analyze your results.

Predict How will the circulatory and respiratory systems and perspiration levels
change in response to exercise? How will the body return to homeostasis?

PROCEDURE
Develop a procedure to test how the circulatory and respiratory systems and SAFETY
perspiration levels change in response to exercise and how the body returns to ideal If the person exercising feels
conditions after exercise. Consider the following questions for your procedure: discomfort at any time, stop the
experiment and inform your
• What will be the role of each team member? Not everyone will exercise. teacher immediately.

• What materials will you need for the experiment?

• How will you measure the response to increased activity?
• How will you you know whether the body systems are in a stable state?
• How many experimental trials will you need? How long will each trial last?
• Which variable will you change, and which variables will be kept constant?
• How will you record your data?
Your teacher must approve your materials list and procedure before you begin.

ANALYZE
1. Graph the measurements you took of changes in the circulatory and respiratory
systems and perspiration levels as a function of how long a person has exercised.
2. Using your data and graphs, determine the effects of exercise over time on the
circulatory and respiratory systems and on perspiration levels.
3. How would you improve your procedure to better collect data for the question
asked in this activity? Did you make any errors that affected your results? What
other measurements could you collect to learn about the effect of exercise?
Image Credits: ©Tom Carter/PhotoEdit

4. How are perspiration levels related to body temperature and homeostasis?

5. Develop a feedback loop to model the relationship between exercise and either
the circulatory system or respiratory system.

Go online to choose one of

DISORDERS OF THE ENDOCRINE SYSTEM EXPLAINING HOMEOSTASIS
these other paths.

Lesson 3 Mechanisms of Homeostasis 45

 EVALUATE

Lesson Self-Check

CAN YOU EXPLAIN IT?

FIGURE 16: Control systems in the skin help conserve body heat.

In the winter, you take steps to help your body maintain its internal temperature by
wearing warm clothes and drinking hot beverages or eating hot soup. Your body also
has its own ways of maintaining its internal temperature in cold weather. When your
body temperature drops below a set point, your brain signals your muscles to contract
and expand rapidly. These contractions, or shivering, generate heat, which helps
increase your body temperature.
Many viruses and bacteria that cause illnesses reproduce best around 37 °C, which is
normal body temperature. To fight off these agents, the body increases its internal
temperature above the normal range. This makes it harder for the virus or bacteria to
reproduce and your immune system can fight it off more quickly. By shivering, your
body is trying to raise its internal temperature to meet the new set point. When the
infection is cleared, your body returns to the set point, and the fever breaks.

Explain Refer to the notes in your Evidence Notebook to explain each of the
following questions. Use evidence from the lesson to support your claims.
1. Why do you shiver when you have a fever?
Image Credits: ©Hero Images/Alamy

2. Is this response an example of positive or negative feedback? Why?

3. How does a fever disrupt homeostasis? Use the terms stimulus, control center,
set point, receptors, effectors, and imbalance in your answer.

46 Unit 1 Living Systems

 CHECKPOINTS

Check Your Understanding 6. People who experience severe blood loss go into a
condition known as hemorrhagic shock. Shock occurs
1. How do stomata function in most plants relative to gas when the blood volume returning to the heart is reduced.
exchange? The heart responds by trying to increase output, which
a. Stomata close to prevent nitrogen from escaping. can result in the patient bleeding to death if they are not
b. Stomata close to allow photosynthesis to occur. treated in time. Is this an example of negative feedback
or positive feedback? Explain your answer.
c. Stomata open to allow carbon dioxide in and oxygen
and water out.
7. Many desert animals are nocturnal, waiting to forage
d. Stomata open to allow water to build up in the plant.
when temperatures are cooler and humidity is greater.
How does this behavior help these animals regulate
2. The circulatory and respiratory systems work together
water balance?
to provide cells with oxygen and nutrients and remove
waste products such as carbon dioxide. When you need
8. What would happen to glucose homeostasis if the
more oxygen, how does the circulatory system respond?
pancreas could no longer produce glucagon?
a. More blood is sent to the lungs and less to the rest of
the body.
9. Exercise increases carbon dioxide levels in the blood. This
b. The blood vessels to the arms and legs constrict to affects homeostasis by decreasing blood pH, which is
conserve oxygen. detected by receptors in the brain stem. The brain stem
c. The heart beats at a faster rate to match the rise in is the control center for gas exchange. Based on this
breathing rate. information, what message would the brain stem send
d. Blood moves more slowly through the organs to carry to the muscles of the diaphragm and rib cage to restore
away more wastes. blood pH homeostasis?

3. What would happen on a hot day if your brain did not

receive input that your body was starting to heat up?
a. You would start to sweat.
MAKE YOUR OWN STUDY GUIDE
b. You would start to overheat.
c. You would start to shiver.
d. You would not feel any effect at all. In your Evidence Notebook, design a study guide that
supports the main idea from this lesson:
4. Flatworms are invertebrates with soft bodies, and
Homeostasis is the regulation and maintenance of the internal
some live in freshwater environments. Based on
environment within a set range that is necessary to support
this information, what can you predict about how a
life at the cellular level.
freshwater flatworm’s body handles osmoregulation?
Select all correct answers. Remember to include the following information in your
a. Excretes dilute urine study guide:
b. Excretes concentrated urine • Use examples that model main ideas.
c. Absorbs as much salt as possible from surroundings • Record explanations for the phenomena you investigated.
d. Excretes as much salt as possible from its body • Use evidence to support your explanations. Your support can
include drawings, data, graphs, laboratory conclusions, and
5. When a newborn baby nurses, the mother’s body is other evidence recorded throughout the lesson.
stimulated to produce milk. What would happen to the
Consider the role positive and negative feedback loops play in
milk supply if the mother chose to bottle-feed rather than
maintaining homeostasis in an organism.
breastfeed? Why?

Lesson 3 Mechanisms of Homeostasis 47

 1.4

Bioengineering

CAN YOU EXPLAIN IT?

FIGURE 1: Technologies, such as pacemakers, can be used to solve health problems.

Prosthetics are an example
of bioengineering.

Gather Evidence
As you explore the lesson,
gather evidence to explain how a
nonliving system can be designed
to work together with a living
pacemaker
system.
electrode

Image Credits: (t) ©MichaelSvoboda/E+/Getty Images; (br) ©Photographer’s Choice/Peter Dazeley/Getty Images
In a healthy heart, the rhythmic beating is the result of carefully timed nerve signals
that spread throughout the cardiac muscle. These signals cause the muscle to
contract in a specific sequence that forces blood to travel through the atria and
ventricles of the heart. When these signals fail to fire correctly, the heart may beat
slowly or erratically, or one or more chambers may not contract properly. If this
occurs, a medical professional may fit a patient with a pacemaker.
Pacemakers are designed to take over or assist the nerve signals that occur naturally
in the heart. The first battery-operated, portable pacemakers were developed in the
1950s. A modern pacemaker, shown in Figure 1, consists of a battery and computer
in the casing with electrodes entering the heart. The electrodes and computer work
together to monitor the heart’s activity and send electric impulses when the heart’s
rhythm is abnormal. The battery provides the power for the electrodes to stimulate
the cardiac muscle.

Predict The batteries in pacemakers do not last forever and eventually need to be
recharged or replaced. What types of features would you need to consider when
designing a better battery for a pacemaker?

48 Unit 1 Living Systems

 EXPLORATION 1

Technology and Living Systems

When you think about the term technology, you probably think of a cell phone or a Collaborate Discuss
tablet computer. Technology is the application of scientific knowledge for practical with a partner three
purposes. Technology does include advanced machines, such as computers and technologies that you used as you
robotic equipment. It also includes simpler items you may not have thought of, such prepared for school today.
as sunglasses, scissors, and pencils.

Technology and the Human Body

Over the course of human history, advancements in science and technology
arose through the process of engineering. Bioengineering applies the concepts of
engineering to living things. Through bioengineering and scientific advancements,
biotechnology has developed that allows people to live longer, healthier lives.

Analyzing Benefits, Risks, and Costs

Every new technology has benefits, risks, and costs. Bioengineers must analyze
these tradeoffs when considering how new or improved technologies can impact
living systems. Decisions must be made about whether a new technology’s benefits
outweigh the associated costs and risks. Benefits are the favorable effects of the
solution, while the costs and risks are the unfavorable effects. A cost might include
the impact on the environment. A risk could be the side effects from using a medical
device. Engineers must balance the benefits, risks, and costs of each design solution.

FIGURE 2: A cochlear implant sends audio signals to the brain.

cochlea

pinna

eardrum
Image Credits: (l) ©iStock/ELizabethHoffmann/Getty Images Plus

For example, cochlear implants increase the hearing ability for people with damaged
inner ears. In a normal ear, the pinna (the ear’s outer portion) funnels sound waves into
the auditory canal. The sound waves then hit the eardrum, causing it to vibrate. These
vibrations are then applified by the middle ear. Hair cells in the cochlea convert the Analyze How does a
waves into impulses that are transmitted to the brain by the auditory nerve. cochlear implant’s process
A cochlear implant, shown in Figure 2, has a microphone and speech processor, which of transmitting sound to the brain
pick up sounds from the environment. A transmitter and stimulator convert signals mimic the process used by the ear?
from the processor into electrical signals. An electrode array implanted into the
cochlea collects the electrical signals and sends them to the auditory nerve.

Lesson 4 Bioengineering 49
 Scientists and engineers continue to modify technology to meet the needs and
demands of society. This often involves increasing the benefits of technology while
reducing the costs and risks. For the cochlear implant, engineers could increase
the benefits by improving the speech recognition ability. They also may work with
scientists to decrease the likelihood of infection, reducing the risk. Engineers may
find new materials that reduce the cost on the environment and reduce the cost
of the implant. A replacement for precious metals in computers could reduce the
environmental impact from mining and make an implant less expensive.

Research and Development

Scientists ask questions to learn more about a phenomenon, and engineers design
solutions to problems related to that phenomenon. This back-and-forth between
scientists and engineers is part of a process known as research and development. The
studies and testing performed during this process often lead to the development and
improvement of technologies.

Explain How are In the case of the cochlear implant, scientists asked questions to learn more about
technology and life the phenomena of hearing. Scientists might have asked, “How do the ear and brain
sciences related in the field interact to detect sound?” or “Which structures are affected in patients with hearing
of bioengineering? loss?” Engineers designed the cochlear implant using information on the mechanics of
hearing that arose from scientific research.

Technology and Society

Technology has greatly influenced society, and society has influenced progress in
technology. New technologies change our lifestyles, diets, and living spaces. Likewise,
as social trends, economic forces, and cultural values change, new technologies
emerge that support these changes. These new technologies also may propel society
toward new changes in culture, health, and the environment.
Consider the advances in emergency medical treatment and technology. Prior to
the 1950s, many ambulances were simply a way to deliver a patient to the hospital.

Image Credits: (r) ©A. Y. Owen/Time Life Pictures/Getty Images; (l) ©Zero Creatives/Cultura/Getty Images
Ambulances only had enough room for a patient in the back, so no medical care
could be given during transport. Changes in societal expectations led to vehicles
with enough room for emergency responders to work on patients, as well as new
technologies to save lives. Modern ambulances continue to undergo design changes
as new medical needs arise.

FIGURE 3: With technological improvements, emergency response time is faster.

Science as a Human Endeavor How have improvements in emergency medical

technology changed our society?

50 Unit 1 Living Systems

 All new technologies come with risks and costs to people and society, no matter how
great the benefits. For example, many vaccines are refrigerated, allowing them to
remain effective for longer periods of time. Refrigeration is rare in some parts of the
world, though, making it difficult for people to access these vaccines. Refrigerants
also add to the greenhouse gas effect. In response, some researchers are turning their
attention to producing vaccines that do not require refrigeration.

Engineering

Clean Drinking Water

FIGURE 4: Societies around the world gain access to clean drinking water through new engineering
designs, such as improved devices to transport water and new wells.

Many people in the world do not have access to clean drinking water. They must Collaborate If you
walk miles to and from wells to bring water to their homes. Once they carry the were asked to design a
water home, it often needs to be filtered to avoid water-borne diseases, such as device to transport water, such
cholera. In response, bioengineers developed better water filtration systems in as the rollers shown in Figure 4,
wells, making the water cleaner and safer. Engineers also developed devices to what societal, cultural, and
make it easier to transport water over long distances, as shown in the left image
environmental impacts would
Image Credits: (l) ©Hippo Water Roller Project; (r) ©ADEK BERRY/AFP PHOTO/Getty Images

in Figure 4. Getting water can be a full day’s work and is often the job of women
you need to consider?
and young girls. By decreasing the time spent focusing on water, women and
girls have more time to devote to other tasks, such as education.

In some cases, by solving one problem, advances in technology can cause new social
and economic problems. Medical technology has enabled many humans to live longer
lives. In some countries, longer life spans mean that the proportion of older individuals
continues to grow, and more resources are needed to support these people.
The environment also is a concern when it comes to new technologies. Disposable
medical supplies make it possible to use sterile equipment on each new patient. Once
used, though, the material needs to be disposed of properly to prevent biohazardous
waste from potentially affecting others.

Explain During the next 50 years, what biotechnology would you like to see developed
or improved? Describe the potential benefits, risks, and costs of the technology and how it
would impact society.

Lesson 4 Bioengineering 51
 EXPLORATION 2

Engineering in Life Science

Engineering and scientific inquiry both involve a set of principles and a general
sequence of events. Scientific investigations often include steps such as asking
questions, making predictions, and investigating the effects of changing variables.
The engineering design process includes steps, such as defining a problem,
developing possible solutions, and optimizing a solution.

The Engineering Design Process

The engineering design process is a method used to develop or improve technology.
The process is iterative, meaning it uses repeating steps. Engineers do not always
apply these steps in the same order. They may skip some on occasion or perform other
steps more than once.

FIGURE 5: The engineering design process is a set of steps that lead to designing or improving a solution to a problem.

DEFINING AND DELIMITING THE PROBLEM DESIGNING SOLUTIONS

Identify the problem/need. Brainstorm solutions.

Conduct research on the Evaluate solutions with respect

problem and previous solutions to the constraints and most
to similar problems. important criteria.

Define and delimit the problem Choose one or two

in terms of criteria and constraints. solutions for testing.

NO Is the problem well-defined? YES Develop and test a model.

YES Does the solution meet the NO

criteria and constraints?
Redefine the problem, if needed, to
clarify the most important criteria.

Consider tradeoffs. Implement the solution and

communicate the results.

Build and test a prototype.

YES
Refine the solution based Is this the best solution in the
on the results of tests. budget or time available?
NO
OPTIMIZING DESIGN SOLUTIONS

52 Unit 1 Living Systems

Following a well-defined set of steps ensures that engineers take a thoughtful and Explore Online
complete approach when designing a solution to a problem. In this process, engineers
Hands-On Lab
must first identify and define the problem or need. In doing so, they may need to
perform research or analyze data to learn more about the problem. They must identify Modeling Joint Movement
aspects that are desired in a final solution as well as the limits on the solution. Next, Use the engineering design process
engineers will begin to design solutions. During this stage, they will evaluate several to develop models of the joints in
different solutions and choose only one or two options to begin testing. In the testing, the skeletal system and test their
or optimizing, stage, designs are tested using computer simulations and prototypes.
ranges of motion.
Based on the results of these tests, the designs may be accepted or refined. The
engineers may even decide to choose a different solution and start the process over.
Imagine that bioengineers are designing a new type of artificial hip. They will need
to research how a normal hip functions and what types of materials are safe to use.
The client that hired the engineers may ask the team to consider using 3D printing to
custom fit the product to each patient. They may also say the design can cost no more
than $10,000. The engineers will come up with many different design solutions, but
only those that cost less than $10,000 will be considered. The final design may not be
3D printed, but it may have other aspects that make it better. Engineers must consider
these types of tradeoffs before presenting their final design.

Collaborate With a partner, discuss why it is necessary for scientific and

engineering processes to be iterative, instead of following a fixed sequence of steps.

Defining and Delimiting the Problem

The first step in the engineering design process is to ask questions that help
specifically define the problem. These questions help an engineer understand the
criteria for the design. Criteria make clear what a successful solution must accomplish
and how efficient and economical that solution should be. These are the “wants” for
the solution. Criteria can include many different aspects of a design, but often cost,
safety, reliability, and aesthetics are considered.
Then, engineers delimit the problem. Delimiting is the process of defining the
limitations, or constraints, of the solution. Constraints are the limitations of a design
and are usually given by the client. These constraints can include things like cost,
weight, dimensions, available resources, and time. Any solution that does not meet the
constraints of the design is not considered.
Engineers often must balance criteria and constraints. They may accept some risks in
tradeoffs, or compromises, for greater benefits. Engineers also may give up one benefit
in favor of another to avoid a potential risk. Consider the artificial hip example again.
Any design that exceeds the $10,000 constraint is not approved. The manufacturer
may consider a design using more typical materials if that reduces a risk or increases
a benefit over using different materials. The benefit of the tradeoff will depend on the
problem defined by the engineer.

Analyze A company is designing an electric wheelchair and hires you as the

engineer. They tell you the wheelchair must not cost more than $5,000. The design
must be usable by people with limited hand movement and should not require a
battery replacement very often. In your Evidence Notebook, define the problem and
then list criteria and constraints for possible solutions.

Lesson 4 Bioengineering 53
 Engineering

Vision Correction Technology

Vision correction has undergone many changes since

FIGURE 6: PRK and LASIK both correct a person’s vision
using a laser, but the technique used will depend on the glasses were first developed in Italy in the 13th century. In
needs of the patient. addition to modern glasses, people with impaired vision
also can buy contact lenses or undergo surgery to fix their
eyesight. LASIK and PRK are two of the more recognizable
PRK LASIK
technologies developed to address vision problems. In
flap LASIK surgery, a blade or laser forms a flap on the outer
surface of the cornea. Then, another laser reshapes the
cornea. In PRK, the surface layer of the cornea is removed
laser laser
beam beam and the corneal bed is reshaped. Doctors and patients
must weigh the criteria and constraints before choosing
a solution. Figure 7 lists several of the criteria for each of
flap these vision correction technologies.
replaced
Analyze Analyze the tradeoffs between each of the
engineering solutions for vision correction technologies in
Figure 7. How would a doctor explain the tradeoffs of each
choice to a patient? What questions might a doctor ask to
help a patient pick the technology that best addresses their
needs and wants?

FIGURE 7: Vision correction technologies have tradeoffs including safety, reliability, cost, and aesthetics.

Technology Eyeglasses Contact Lenses LASIK PRK

Safety Provides sun protection Provides sun protection Cannot provide sun or Cannot provide sun or
and physical protection but not physical protection. physical protection. Procedure physical protection.
for the eyes. Infections are possible if is generally safe. Relatively Procedure is generally safe.
lenses are not cleaned often. short recovery time. Longer recovery time.
Reliability Can be lost or broken. Can be lost or torn. Results are relatively Results are relatively
Lenses or frames can be Can be replaced as needed. permanent. Glasses may permanent. Glasses may
replaced as needed. become necessary. become necessary.
Cost Prices range from tens Prices range from tens Prices are typically in the Prices are typically in the
to hundreds of dollars. to hundreds of dollars. thousands of dollars. thousands of dollars.
Aesthetics Come in many colors and Come in many colors. Do not Does not obscure facial Does not obscure facial
shapes. May obscure some obscure facial features. features. Eye color cannot be features. Eye color cannot
facial features. altered. be altered.

Engineers prioritize criteria by deciding which ones are most important for a given
problem. They make tradeoffs between them to begin brainstorming solutions to
the problem. Engineers may even redefine the problem to clarify the most important
criteria before beginning to design and test a solution. Remember, if a proposed
solution does not meet the constraints of the problem, it will not move forward in the
engineering design process.

54 Unit 1 Living Systems

 Designing Solutions
After engineers have identified the constraints and criteria for solving a problem, the
next step is to brainstorm design ideas for a solution. Usually, engineers and other
specialists work in teams when brainstorming. The group leader presents the problem
to be solved and encourages all ideas to be suggested, even if they seem outrageous.
Once the team has brainstormed several ideas, they may use a decision matrix, or
Pugh chart, to evaluate each solution against the criteria of the problem. In a decision
matrix, each criteria is given a number, or weight, based on how important that criteria
is. The more important the criteria, the greater the weight assigned to it. Then, each
design is rated based on how well it meets those criteria. The scores for each design
are multiplied by their respective weights, and the products are totaled so engineers
can determine how well the design is meeting the criteria. They may choose to take
the design with the highest score to the next phase, or they may choose to brainstorm
new ideas if no designs meet the requirements.

FIGURE 8: An example decision matrix for three water filtration system designs, weighted
on a scale from 0 to 5

Design Criteria Weight Design 1 Design 2 Design 3

Safety 5 4 1 5
Reliability 4 2 3 4 FIGURE 9: Examples of different
Cost 2 1 2 1 CPAP designs

Aesthetics 1 1 1 0
Total Points 31 22 43

Figure 8 shows how a decision matrix can be filled out for three designs. In this
example, each column represents a different design for a new water filtration
system people can use in their homes. Safety is weighted a 5, meaning it is extremely
important. Aesthetics, though, are weighted very low, meaning they are not as
Image Credits: (t) ©Brian Chase/Shutterstock; (c) ©JPC-PROD/Shutterstock; (b) ©Phanie/Phanie/Superstock

important. To determine how to weight each design, engineers may choose to make
a model or run computer simulations to see how each design would work in a typical
situation.
A bioengineer may use a decision matrix to evaluate a technology, such as a new
design for a Continuous Positive Airway Pressure (CPAP) machine. These machines are
worn by people who suffer from sleep apnea, a condition where breathing starts and
stops during sleep. CPAP machines are worn while a person is sleeping and supply a
constant source of pressure to help keep their airways open. The criteria for a machine
like this would likely include safety and reliability but also may include comfort, ease of
use, and noise level.

Engineering Make a decision matrix for the three CPAP machines shown in
Figure 9. What criteria do you think are important for this machine? How would
you weight them?

Once a number of solutions are proposed, they are evaluated against the criteria and
constraints set out for the desired solution. Solutions that do not meet the constraints
must be redesigned if they are to be considered. In general, one or two ideas that
best meet the criteria and all constraints are selected, and these ideas enter the
optimization phase of the design process.

Lesson 4 Bioengineering 55
 Optimizing Design Solutions
When one or two solutions have been chosen, engineers may build a prototype of the
technology to further test the capabilities and effectiveness of the design. A prototype
is the first build of a design and may not be built to scale or with the final materials.
Since the results from testing the prototype may result in design changes, prototypes
are often built with cheaper materials than the final version. This way, engineers can
run many tests and build many versions of their designs. As the design becomes more
refined and finalized, engineers may begin to use the final materials to ensure the
solution will work as expected.

Analyze What types of information can be gained from building a prototype that is
not an exact model of the final product?

Engineering

Optimizing Prosthetics

One of the biggest challenges often facing designers is the need to think creatively
and to seriously consider new designs. While not traditional, these new designs
may be what are required to solve a problem or improve an existing product. Van
Phillips engineered the “blade” prosthetic leg/foot now preferred by runners. His
design abandoned the traditional clunky prosthetic, favoring lightweight materials
tailored to athletes, as shown in Figure 10.

FIGURE 10: Prosthetic leg designs have changed over time. As new materials are
developed, new ideas are generated.

Collaborate
Discuss this question
with a partner: How have
advances in the different fields
of science and engineering
influenced prosthetic limb
technology?

56 Unit 1 Living Systems

 Testing is an important part of the engineering design process, allowing engineers to
get feedback on the design. Data collected from tests will tell engineers if their design
is working as expected. The data also may show design problems that were not seen
in early stages of the process. Engineers will review these issues and determine which
ones need to be fixed. Considering tradeoffs is an important part of the optimization
process. Issues that do not seriously impact important criteria or constraints may not
be corrected if the tradeoff is undesirable, such as increasing the cost of the design.
However, if the problem is important enough, engineers may need to change the
design or brainstorm new designs to address the concern.

FIGURE 11: Engineers may return to a design or a prototype during the optimization
process.

Language Arts
Life cycle analyses are another way to evaluate a design. A life cycle analysis attempts to
Connection
evaluate the real cost of a new technology or design. It takes into account the materials
and energy used to manufacture, transport, use, and dispose of a product. Perhaps
Research the life cycle of different
one design has several benefits over another. If the design is much more expensive to cell phones. How long are they built
produce, manufacturers might abandon it in favor of another, less expensive design. If to last? What are the energy
it wears out quickly and needs to be replaced often, the design might be abandoned in requirements to manufacture a
favor of a more durable alternative. phone? Develop your own life cycle
Life cycle analysis also considers the environmental impact of the materials and wastes
analysis of a phone to determine
from producing the design. Engineers might consider an alternative if manufacturing the true cost of the technology.
a design produces pollution. If the product cannot be thrown away safely, a
biodegradable or recyclable option may be considered.
Engineers may also run a cost-benefit analysis to further evaluate their design solution.
A cost-benefit analysis is a method of identifying the strengths and weakness of a
design. The cost could be the monetary cost to produce the design. If the device
costs too much to make and the benefits are not great enough, the design solution
may be disregarded in favor of a less expensive design. A cost also could be related to
environmental factors. If a design uses a very rare metal and will result in large-scale
mining, the environmental impact may outweigh the benefits, especially if a different
material could be used.
Image Credits: ©Tim Pannell/Corbis/Getty Images

When a final design has been chosen and fully tested, engineers will communicate their
results. This may just involve presenting the final solution to the client to begin production.
If the design is new or groundbreaking or has important implications, the engineering
team may publish a journal article detailing the design to the scientific community.

Explain How do you think the engineering design process differs for biotechnologies,
like pacemakers, used in the medical field compared with that used in other fields of
technology, like in developing a cell phone?

Lesson 4 Bioengineering 57
 CONTINUE YOUR EXPLORATION

Careers in Science

Careers in Bioengineering

Bioengineering includes a variety of fields, such as biomedical First, the engineering team must define and delimit the
engineering, cellular engineering, molecular engineering, and problem. The constraints were given by the company: The
others. Bioengineers use engineering methods and biological design must cost less than $30,000; it needs to be completed
science to design and manufacture equipment, computer in half a year; and all components need to last at least five
systems, and new materials used in the field of biology. years. The criteria for this problem may include weight,
hydrodynamics in the water, and safety of use.
Biomedical Engineering Once the problem is defined, engineers will begin
Devices made by biomedical engineers include artificial brainstorming possible designs. Each proposed design will
joints and organs, prosthetics, corrective lenses, and dental be evaluated, and the solutions that meet all constraints
implants. Biomedical engineers still use the engineering and the most important criteria will be chosen for testing.
design process to help them develop and optimize medical When developing prosthetics, engineers may run computer
technologies. In this field, engineers must always consider simulations and use other types of models to help evaluate
how a design will interact with the different systems of the each solution. The team may realize that traditional prosthetic
human body. materials are too heavy to be used for an aquatic prosthetic.
Instead, they may research more lightweight materials.
FIGURE 12: Biomedical engineers design devices, such as
prosthetic limbs. This prosthetic limb is designed to interpret The engineering team will then begin testing and optimizing
messages from the user’s nervous system. their designs. They will build prototypes and may even fit
their prototype to swimmers to get feedback and data on
the design. At this stage, engineers may realize their design
generates too much drag in the water and needs to be
redesigned to be more streamlined.
Even when the client approves a solution, engineering teams
may continue to review designs and make improvements.
As technology changes, there are new opportunities for
improved design concepts.
Working with a team, develop your own design of an aquatic
prosthetic leg. Imagine you are working with the same

Image Credits: ©Laura Lean/PA Wire URN:23312103 (Press Association via AP Images)
constraints outlined in this example. With your group:
Define and delimit the problem In your group, outline the
A bionic hand, as shown in Figure 12, might interact with criteria and constraints and then clearly define the problem.
the nervous system to interpret signals to grasp an item.
Design a solution Each individual in your group should
However, implanting such a device could cause a stress on
propose a potential solution. Assign weights to the criteria
the immune system, causing the body to reject the device.
your group outlined, and make a decision matrix to evaluate
Biomedical engineers must consider all potential health risks
each design. Choose the highest-rated design, or brainstorm
when designing solutions.
additional ideas until you find a solution that solves the
Imagine that a company wants to develop prosthetics for problem your group outlined. Remember, you may need to
competitive swimmers who have had one of their legs redefine the problem if the design solutions do not meet
amputated at the knee. The company needs a working design the criteria or constraints. When your final design has been
within six months and wants each prosthetic to cost less than chosen, make a model, such as a drawing, of that design and
$30,000. The prosthetic must last a swimmer at least five have your teacher approve it before moving to the next stage
years before any parts need to be replaced. How would an of the process.
engineering team solve this problem?

58 Unit 1 Living Systems

 Develop a prototype Using common household and
FIGURE 13: Bioengineers develop technologies, like MRI
classroom items, develop a prototype of your approved
machines, to help scientists learn more about living systems.
design. You may use items such as paper towel rolls, PVC
tubing, cardboard, tape, and any other items you may need.
Remember, a prototype does not need to be a replica of the
final product. Your prototype may not be made to scale or
it may not be waterproof. The prototype should be able to
demonstrate how the design will work, but it does not need
to function completely.
Optimize the design After building your prototype, review
your design and identify areas where the design could be
improved. Review the criteria and constraints again to ensure
your design is solving the problem. If you feel your design
did not work, brainstorm new designs or ways to change
aspects of your designs. You may wish to build an additional
prototype to test your modifications.

Language Arts Connection With your group,

research other designs for prosthetics that help people
swim. Then, make a presentation to share with the class.
In your presentation:
Molecular Engineering
• Include a summary of your research and the
prosthetic designs you discovered. Molecular engineering is a highly integrated field of study
• Present a diagram of your final design to the class. combining knowledge from biology, chemistry, mechanics,
• Explain the most important criteria considered in and materials science. Molecular engineers study ways to
designing your solution. build better materials and systems by studying the molecular
properties of those materials.
• Finally, present your prototype and explain how your
design will solve the problem. In the field of biology, molecular engineers are studying
immunotherapy. Immunotherapy is the treatment of disease
by amplifying or minimizing the body’s immune response.
Cellular Engineering Molecular engineers are developing vaccines to increase
Cellular engineering is a field of bioengineering that patients’ immune responses.
combines an understanding of cellular functions, biological
Molecular engineers also are researching ways to edit and
systems, and engineering practices to develop technologies
manipulate an organism’s genetic material. This may allow
that help improve people’s lives. For example, cellular
them to treat or cure genetic disorders, modify metabolic
engineers may study ways that stem cells can be used to
rates, and modify the structure of proteins to make new
improve the lives of people with medical conditions, such as
functions. To make changes to the genetic material of
Parkinson’s disease or diabetes.
an organism, molecular engineers are developing new
Tissue engineering uses aspects of cellular engineering to technologies to help further their research.
develop biological tissues. Whole tissues or portions of tissues
can be made from cells and then used to repair damaged Language Arts Connection Write a short
areas of the body. Scientists in this field are even trying to newspaper-style article comparing and contrasting the
make entire organs using their understanding of cellular
different fields of bioengineering.
function, engineering, and biological systems.
Image Credits: ©Corbis

Go online to choose one of

3D BIOPRINTING NANOTECHNOLOGY
these other paths.

Lesson 4 Bioengineering 59
 EVALUATE

Lesson Self-Check

CAN YOU EXPLAIN IT?

FIGURE 14: A pacemaker is a nonliving system that functions inside a living system,
the human heart.

pacemaker

electrode

Pacemakers generate electrical signals that stimulate the heart when cardiac activity is
abnormal. The pacemaker has gone through many design changes based on improved
technology and medical knowledge since its initial conception. As technologies
improved, designs became smaller. As scientific understanding of anatomy, heart
conditions, and biological systems progressed, so did the efficiency of pacemakers.
Scientists and engineers continually work together to improve upon this design and
many others in the medical field.

Explain The batteries in pacemakers eventually need to be recharged or

replaced. What types of features would you consider when designing a better
battery for a pacemaker?

When designing a new component for a device, engineers will still use the engineering
design process. The process is iterative, so the steps may not be applied in the same
order. For example, when designing a new battery for a pacemaker, engineers may

Image Credits: (r) ©Photographer’s Choice/Peter Dazeley/Getty Images

start by testing pacemakers and existing batteries. The data gathered in these tests
may help them brainstorm new ideas for how to improve the previous design.
The engineering team also will have different constraints when improving a design
than when creating a new design. For example, engineers will only be able to develop
batteries that fit inside the existing pacemaker and work with the components already
in the design. They also may be working within a shorter timeframe and a smaller
budget than if they were developing a new pacemaker design.
By working with patients, doctors, and manufacturers, engineers can identify the most
important criteria to incorporate into their design. Perhaps patients would rather have
a battery that is easier to recharge than one that lasts a few years longer and needs
to be replaced. Once engineers understand the limitations in the current design, the
constraints, and the important criteria, they can begin developing new designs.

60 Unit 1 Living Systems

 CHECKPOINTS

Check Your Understanding 6. Make a decision matrix to compare three models of a

device, perhaps personal tablet devices or phones. Use
1. Imagine that you are an engineer who designed a the following questions to build the matrix and evaluate
prototype for a client. After testing the prototype, you the results:
discover it does not address the client’s needs. What a. What design criteria are most important?
might be a possible next step in the process? b. How would you weight these criteria?
c. How would the competing designs score on each
2. You and a partner have brainstormed a design for an criterion?
implanted device to help keep insulin levels in check for
d. Which design(s) should move to the next stage of the
a person who is diabetic. What should be the next step in
process and why?
the design process?
a. test on a patient
b. build a prototype
c. revise the design
MAKE YOUR OWN STUDY GUIDE
d. evaluate the design
In your Evidence Notebook, design a study guide that
3. Which of the following technologies would likely involve
supports the main ideas from this lesson:
a bioengineer to design and build? Select all correct
answers. Bioengineering is the application of engineering processes and
a. artificial heart valve practices to living things.
b. tablet computer Engineering develops and modifies technological solutions for
c. artificial hip joint the needs of society.
d. global positioning system
Remember to include the following information in your
e. automobile engine
study guide:
f. surgical robot
• Use examples that model main ideas.
• Record explanations for the phenomena you investigated.
4. A biomedical engineer is developing a portable medical
• Use evidence to support your explanations. Your support can
imaging machine designed to be used in remote areas or
include drawings, data, graphs, laboratory conclusions, and
in situations where a natural disaster has made access to
local imaging facilities difficult. She made a list of criteria
other evidence recorded throughout the lesson.
and constraints for the new device. Which of these should Consider how bioengineering solutions influence the environment
be classified as criteria? Select all correct answers. while addressing the wants of society.
a. transmits information wirelessly to base medical facility
b. one person can carry it without assistance
c. uses a rechargeable battery
d. case made of high-impact plastic
e. generates high-definition CT scans
f. completes scans rapidly

5. One of the ways in which society impacts technology

is through government regulation. Describe how
government regulation can have both positive and
negative impacts on technology.

Lesson 4 Bioengineering 61
 A BOOK EXPLAINING
COMPLEX IDEAS USING
ONLY THE 1,000 MOST
COMMON WORDS

BAGS OF STUFF
INSIDE YOU
Parts of your body and
how they work together
You know that an organ system is two or more organs
working together to perform body functions. Here’s a RANDALL MUNR
OE
XKCD.COM
look at several organ systems in the human torso.

62 Unit 1 Living Systems

 YOU ARE
HERE

THIS IS WHAT YOU THINK WITH.

HOLE TO OUTSIDE When you read words (like these),
This hole is in your nose. It this part of your body turns them
helps you breathe and lets into ideas.
you smell things. By choosing the right words, you
can take an idea that’s happening
in your head and try to make an
HOLE TO OUTSIDE
idea like it happen in someone
This is the hole in your else’s. That’s what’s happening
mouth. It’s where air goes in right now.
and out, food goes in, and
words come out.
Note: Some people don’t
like it when you make words
come out while you’re putting BLOOD
food in. (to your arms
THINKING
and the rest
BAG
HEAD MOUTH WATER MAKER
of your head)
PARTS
This makes the water in your This pushes
mouth that helps food fi t on your blood
down your neck. about once a
second to send
it around
your body.

AIR BAG AIR BAG BLOOD

PUSHER

These add air to your blood.

CHEST They get bigger and smaller to pull
PARTS and push air in and out.

PART BREAKER
Sometimes, blood gets
stuck in here.
That’s one of the biggest
BLOOD CLEANER reasons people’s bodies
stop working.
BLOOD This bag breaks tiny things into even BLOOD HALLWAYS
(from other smaller, simpler parts they’re made These carry blood around your
body parts) of. Your body uses it in many ways, body. If you get a hole in them, the
like to get rid of the stuff in wine that blood starts to fall out. If this starts
makes you feel strange (which keeps happening, it can be a big problem,
you from feeling strange forever). It and you should fix it fast.
also makes water for your hallways. If
this bag has a problem, your eyes turn
yellow and your body stops working.

Unit 1 Thing Explainer 63

 BAGS OF STUFF INSIDE YOU

Sometimes, this opening FOOD BAG FEAR WATER

gets blocked. Then, when This holds and breaks up These make a kind of water
you eat rich food and the food using special water. that makes your body feel
bag tries to push water afraid or excited.
CHEST out, it hurts.
PARTS

WATER FOR RICH

FOOD
This holds water for
breaking down rich
food (like the yellow
stuff you spread).
When you eat rich BLOOD
food, this pushes out (to other
water to break body parts)
it down.
SMALL FOOD HALLWAY
This hallway is where a lot
of food gets broken down
and the stuff your body
SPECIAL WATER needs is taken out.
MAKER The hallway is about as
This bag makes long as a car. It makes
some of the waters a lot of turns so it can fi t
that help turn food in your stomach.
into power. If it goes EXTRA PART
wrong, you can have This doesn’t seem
BIG FOOD HALLWAY
a problem where you to do anything.
This hallway is
get too much or too Sometimes it has a
wider than the small
little sweet stuff in problem and doctors
hallway, but shorter.
your blood. have to take it out.
This is where your
LIFE INSIDE YOU body takes extra
There are a lot of water out of the
living things in these food so you don’t PARTS FOR
hallways that help you need to drink as MAKING MORE
break down different much water. OF YOU
kinds of food.
These parts can
USED FOOD HOLDER make new people.
Once you’re done with
food, it waits here until
you push it out.
HOLE TO OUTSIDE HOLE TO OUTSIDE In about half
Food comes out here If your body makes a of all people
when you’re done new person, it comes these go to a
eating it. out of here. About half single opening.
of all people have this.

64 Unit 1 Living Systems

 Go online for more
about Thing Explainer.

AND NOW
YOU ARE
HERE

BLOOD CLEANERS
These look for stuff in your blood that you’re
done with or have too much of—like extra
sweet stuff, or stuff from the doctor that you
ate to feel better—and send it to be pushed
out of your body.

YELLOW WATER HALLWAY

WHITE BLOOD RED BLOOD
Most of the time, the water from your blood
PIECES PIECES
cleaners is yellow, but eating certain colorful
foods can make it change color for a while.
(If it turns dark or red, it may mean
you’re sick.) PUSHED TOGETHER
In real life, these parts are all pushed
together inside your chest like this.

BODY PLAN HOLDERS

These parts hold lots of plans for
new people. Each plan is made from Air bags
pieces of the plans used to make you.
These parts also control how your
voice, hair, and body grow.

LOWER
YELLOW WATER HOLDER PARTS
This holds yellow water until
you push it out.

Part
Image Credit: ©Kenneth Eward/BioGrafx/Science Source

HOLE TO OUTSIDE breaker

The yellow water from your
blood comes out here.
Food
Large bag
food
hallway

Small food
hallway

Unit 1 Thing Explainer 65

 UNIT CONNECTIONS

Technology Connection FIGURE 1: Computers, like this laptop,

are made up of components.
Computer Systems Computers and people have more in common than you might
think. Computers are systems that use hardware and software to store, manipulate,
and analyze data. People are living systems that use smaller systems to survive
and reproduce. Computers have many components that have a similar function to
human structures or other living systems. For example, a processor is a computer’s
control center, much like a brain is a person’s control center. Computers can be
part of a larger system, or network, just as people are part of larger systems like
populations and ecosystems.

Using library and Internet resources, research computer systems. Create and label a
diagram of a computer system that describes how the computer is made up of
smaller systems, how it links to other larger systems, and how information and energy flows
among systems. Make a list of questions you would ask about the relationship between
people and computers based on the diagram you develop.

Music Connection FIGURE 2: Listening to and playing

music has been linked to health and
medical benefits.
Your Body on Music Have you ever felt calm, excited, or sad while listening to
music? This is because music can affect your mood. Multiple studies have shown
that music has other effects on the human body, such as increasing cognitive
abilities and lowering blood pressure. Music can even be used as a therapy to
decrease the symptoms of heart disease.

Using library or Internet resources, research the effects playing and listening to

Image Credits: (t) ©Muriel de Seze/DigitalVision/Getty Images; (c) ©Corbis/Steve Hix/Getty Images; (b) ©Courtesy of NASA
music can have on the human body. Evaluate the claims and evidence provided,
then construct an argument either for or against using music as a medical therapy. Write a
blog entry to convince others of your argument. Support your argument with specific text
evidence from reliable, scientific sources.

Earth Science Connection

FIGURE 3: Exercise in space slows
muscle loss and mineral loss in bones.
Humans in Space Living in space is tough on the human body. Zero gravity
environments negatively affect balance, coordination, muscle strength, and bone
density. Isolation in confined spaces can lead to sleep and mood disorders and poor
nutrition. The radiation levels in space are more than ten times the levels found on
Earth. All of these problems must be solved for humans to safely live away from
Earth for long periods of time.

The effects of space on the human body can be reduced through engineering. For
example, some astronauts use specialized machines to exercise in space. Collaborate
with a group to develop a prioritized list of criteria and constraints that an engineer might
consider when designing an apparatus to combat the effects of space on the human body.

66 Unit 1 Living Systems

UNIT PRACTICE AND REVIEW

SYNTHESIZE THE UNIT DRIVING QUESTIONS

Look back to the Driving Questions from the opening section

In your Evidence Notebook, make a concept map, of this unit. In your Evidence Notebook, review and revise
graphic organizer, or outline using the Study Guides you your previous answers to those questions. Use the evidence
made for each lesson in this unit. Be sure to use evidence to you gathered and other observations you made throughout
support your claims. the unit to support your claims.

When synthesizing individual information, remember to follow

these general steps:
• Find the central idea of each piece of information.
• Think about the relationships between the central ideas.
• Combine the ideas to come up with a new understanding.

PRACTICE AND REVIEW

1. How does organization make it possible for the human Use the information from Figure 4 to answer Question 4.
body to carry out the wide range of interactions
necessary for survival? Cortisol Concentrations over a 24-Hour Period
a. Cells are the foundation of the human body and each FIGURE 4: Cortisol concentrations change throughout the day.
cell can carry out all interactions necessary for survival.
b. Tissues are the highest level of organization in the
human body and tissues are capable of carrying out
specialized tasks necessary for survival.
c. Levels of organization make it possible for cells,
Cortisol concentration

tissues, organs, and organ systems to specialize and

take on specific functions.
d. There is no overlap in the organization and interaction
of organ systems, making it possible for the body to
fulfill a wide range of life functions.

2. Select a relationship that is similar to the following

relationship: neuron : send electrical signal 1 12 24
Hour of day
a. cardiac cell : muscle cell
b. muscle cell : contraction
c. circulatory system : blood cell 4. Cortisol is produced at certain times of the day, as shown
in the graph. Cortisol has a positive feedback on Process
d. homeostasis : endocrine system
A, which outputs Substance Z. At what time of day will
the concentration of Substance Z be at its highest if there
3. A newly discovered organism has cells with large fluid-
is no other feedback on Substance Z?
filled sacs in the middle. Considering current scientific
a. morning
knowledge about the structure and function of cell
organelles, what is a likely function of these structures in b. afternoon
the new organism? Select all correct answers. c. evening
a. store water and waste d. late night
b. store genetic information
c. produce sugar
d. strengthen the cell

Unit 1 Unit Closer 67

 UNIT PRACTICE AND REVIEW

Use the following information and the diagram to answer 8. What evidence supports your model and your claim
Questions 5–8. for Question 7? Provide evidence and explain your
reasoning.
The pituitary gland regulates the concentration of
water in blood by releasing higher or lower levels of the
antidiuretic hormone (ADH). ADH increases the amount of 9. Imagine a solution for a problem scores high for all
water reabsorbed from urine by tubules in the kidneys. criteria but violates one of the constraints. What is the
relationship between the solution and the problem?
FIGURE 5: The pituitary gland controls the concentration a. The solution will work for the problem because it does
of water in blood. not have to satisfy every constraint.
b. The solution may work for the problem if there is a
Concentration Concentration trade-off between criteria and constraints.
of water in of water in
c. The solution is not viable for the problem as it is
blood rises. blood falls.
currently defined and delimited.
d. The solution will never be successful and should be
Pituitary gland Pituitary gland abandoned.
releases Homeostasis releases
less ADH. more ADH.
10. Imagine your team is developing technology to perform
less invasive angioplasty, a surgery typically used to
Kidneys reabsorb Kidneys reabsorb unblock arteries in the heart. You have two solutions.
less water. more water. Urine Both solutions are equally effective and safe. Solution
Urine is dilute. is concentrated. 1 costs less than Solution 2. Solution 2 is made from
recycled materials and has a lower environmental impact
than Solution 1. What is a likely next step to help you
5. Which sequence models the correct flow of information choose between the two solutions?
in this feedback loop?
a. Prioritize cost and environmental impact to decide
a. pituitary gland → kidney tubules → pituitary gland which solution is best for this problem.
b. kidney tubules → pituitary gland → water b. Redefine the problem and optimize the two solutions
concentration in blood to solve the new problem.
c. water concentration in blood → kidney tubules → c. Design a solution that is cheaper and has a lower
pituitary gland environmental impact than both Solution 1 and
d. water concentration in blood → pituitary gland → Solution 2.
kidney tubules d. Add constraints until one solution is no longer viable.

6. How does this feedback loop demonstrate multiple body

systems working together to maintain homeostasis?
a. The pituitary gland works with the kidneys to regulate UNIT PROJECT
the water concentration in blood.
b. The pituitary gland is part of the endocrine system, Return to your unit project. Prepare your research and
which interacts with the excretory and circulatory materials into a presentation to share with the class. In
systems to regulate water concentration in blood. your final presentation, evaluate the strength of your
hypothesis, data, analysis, and conclusions.
c. The pituitary gland is part of the nervous system,
which interacts with the digestive and immune Remember these tips while evaluating:
systems to regulate water concentration in blood.
• Look at the empirical evidence—evidence based on
d. The pituitary gland maintains homeostasis, the observations and data. Does the evidence support
kidneys regulate the water concentration in blood, the explanation?
and blood circulates to deliver water to cells. • Consider if the explanation is logical. Does it
contradict any evidence you have seen?
7. Imagine a disorder that prevented kidney tubules from • Think of tests you could do to support and
reabsorbing water from urine. Draw a model that explains contradict the ideas.
how this change would affect this feedback loop.

68 Unit 1 Living Systems

UNIT PERFORMANCE TASK

Analyzing a Disease Outbreak

Greenfield, a small town in south Texas, has seen a recent
FIGURE 6: Clinical symptoms presented in the twenty-five
outbreak of sickness involving unexplained high fevers. All undiagnosed high-fever cases, Greenfield, TX, 2016
symptoms reported are shown in Figure 6. The town lacks
the medical expertise and laboratory resources to properly Number of Affected
diagnose the medical cause of the high fevers. Town residents Symptoms Individuals
need information about what is causing the outbreak, why
Fever (body temperature > 38.5 °C) 25
the symptoms are occurring, and how further cases can be
prevented. The only other thing that seems out of place in Discomfort 19
Greenfield is the large flea population. What information can
Headache 17
you provide to the residents of Greenfield?
Muscle ache 16
1. DEFINE THE PROBLEM Chills 16
With your team, write a statement outlining the problem Rash 11
you’ve been asked to solve. Record any questions you have
on the problem and the information you need to solve it. Light sensitivity 7
Confusion 3
2. CONDUCT RESEARCH
With your team, investigate all of the information you’ve been
given about the outbreak in Greenfield. What is the most
likely disease causing the outbreak?

CHECK YOUR WORK

3. DEVELOP A MODEL
On your own, analyze the problem you’ve defined along with
your research. Make a model that demonstrates how the A complete presentation should include
disease is transmitted and how the body systems are working the following information:
together to combat the infection. Your model should also • a clearly defined problem with supporting questions
show why the symptoms are occurring and how homeostasis
that are answered in the final presentation
is involved in the immune response.
• a model of disease transmission and immune
response in humans
4. IDENTIFY A SOLUTION • a recommendation that explains how to solve the
Provide a range of solutions for how the town can avoid problem and uses evidence to support the solution
further outbreaks of this disease. • images and data that further support your solution

5. COMMUNICATE
Present your findings to the town residents, explaining
the most likely cause of the disease, why the symptoms
are occurring in relation to the immune response and
homeostasis, and your proposed solutions for preventing
further outbreaks. Your presentation should include images
and data to support your claims.

Unit 1 Unit Closer 69