Name ______________________________ Class ___________________ Date __________________
Human Systems and Homeostasis
Study Guide B
Answer Key
SECTION 1. LEVELS OF
ORGANIZATION
SECTION 2. MECHANISMS OF
HOMEOSTASIS
1. Stem cells go through two processes to
become specialized cells.
2. Determination—stem cells commit to
becoming only one type of cell. Examples:
muscle, nerve, skeletal cells
3. Differentiation—committed cells acquire the
structures and functions of specialized cells.
Examples: muscle cells become cardiac,
smooth, or skeletal muscle cells
4. Stem cells contain all the genes for a
complete organism, and they can become
any one of the more than 200 different types
of cells in the body.
5. Examples: bundled muscle cells that can
extend and contract, bundled epithelial cells
with cilia that line intestinal organs, sperm
with whip-like tails, porous bone cells
6. Examples: sperm tails allow sperm to move;
long extensions of nerve cells allow them to
communicate with other cells; bone cells are
porous to allow nutrients to reach bones;
epithelial cells are closely packed to provide
more surface area; smooth and skeletal
muscle cells are bundled together and
elongated, which allows for stretching and
contracting
7. specialized cells—the smallest units of life
with specialized structures and functions;
tissues—groups of similar cells that work
together to perform a specialized function;
organ—different types of tissues that
function together; organ system—two or
more organs working in a coordinated way;
organism—life form made up of different
organ systems functioning in a coordinated
way to maintain life
8. Determin- = the cells determine to be of one
particular type of cell Different- = the cells
acquire their different structures and
functions
1. The sensors may continue to send a signal,
but homeostasis could not be maintained.
2. sensors—gather information on
internal/external conditions. control
center—receives information from
sensors, compares to set points; sends
messages. communication system—nerves
and hormones carry signals to targets.
targets—organs, tissues respond to
messages to restore homeostasis
3. The sensors may continue to send a signal,
but homeostasis could not be maintained.
4. Diagram “A”—negative feedback; diagram
shows change away from a set value is
counteracted. Diagram “B”—positive
feedback; diagram shows change away from
a set point is increased, then returns to
normal
5. Negative—it is counteracting a change away
from a set point for internal body
temperature by releasing fluid from the
sweat glands to cool the body.
6. As activity increases, sensors send messages
to the brain. The brain detects low oxygen
levels and sends messages to the heart and
lungs to work harder and bring more oxygen
into the body.
7. negative feedback loops counteract any
change away from set points; positive
feedback loops increase change away from
set points until a certain result is achieved
8. Sample answers: pilot or navigator on plane
keeping it on course; thermostat on furnace
or air conditioner; guidance system on a
space craft; building sprinklers turning on
when a fire starts
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
i
Human Systems and Homeostasis
Name ______________________________ Class ___________________ Date __________________
Study Guide B continued
SECTION 3. INTERACTIONS AMONG
SYSTEMS
1. Sample answers: members of a sports team,
or an orchestra, or a touring rock band, or a
construction crew, or a movie production
working together; each individual has a job
to do, but all must work together for the
enterprise to succeed
2. Skin—absorbs UV light to make an inactive
form of vitamin D; Liver—changes inactive
form of vitamin D into another compound;
Kidneys—converts compound into active
vitamin D
3. Hypothalamus acts as a control center that
receives data about body temperature and
sends messages to target organs in the skin,
respiratory, and circulatory systems.
4. Any of the following: external or internal
conditions change too rapidly, serious
injuries overwhelm homeostatic
mechanisms, sensors fail to detect internal
5.
6.
7.
8.
9.
10.
11.
or external changes, wrong messages are
sent or targets fail to respond, viruses or
bacteria change the body’s internal
chemistry
Long-term disruptions over time affect more
and more organs and organ systems,
resulting in greater damage to the body.
short term
little lasting damage
common cold
long term
diabetes
Sample answer: a thermostat or closed
circuit or a balance tray that is returned to a
center point.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
ii
Human Systems and Homeostasis
Name ______________________________ Class ___________________ Date __________________
Section 1: Levels of Organization
Study Guide B
KEY CONCEPT
The human body has five levels of organization.
VOCABULARY
determination
organ
differentiation
organ system
tissue
MAIN IDEA: Specialized cells develop from a single zygote.
Fill in the main idea and supporting information for cell development.
1. Stem cells:
2. Determination:
3. Differentiation:
4. What are the characteristics of stem cells?
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_______________________________________________________________
5. Look at Figure 1.2. Describe some of the shapes and structures that the cells in
this figure acquired during differentiation.
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_______________________________________________________________
_______________________________________________________________
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
1
Human Systems and Homeostasis
Section 1: Levels of Organization
Name ______________________________ Class ___________________ Date __________________
Study Guide B continued
6. Give two examples of how cell structures relate to cell functions.
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
MAIN IDEA: Specialized cells function together in tissues, organs, organ
systems, and the whole organism.
7. Write a description of each level of organization and draw a sketch to help you
remember it.
Level of Organization
Description
Sketch
Vocabulary Check
8. There is an easy way to remember the difference between determination and
differentiation. Look at the first part of each word. Explain how these word
parts can help you remember the meaning of each term.
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_______________________________________________________________
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
2
Human Systems and Homeostasis
Section 1: Levels of Organization
Name ______________________________ Class ___________________ Date __________________
Section 2: Mechanisms of Homeostasis
Study Guide B
KEY CONCEPT
Homeostasis is the regulation and maintenance of the internal environment.
VOCABULARY
homeostasis
negative feedback
feedback
positive feedback
MAIN IDEA: Conditions within the body must remain within a narrow range.
1. Give two reasons why it is so important that the internal environment of the
body remains stable.
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
2. Homeostasis is maintained by control systems. Fill in the name and function of
the parts of the control system in the cycle diagram below.
Sensors
Control center
Targets
Communication system
3. What might happen if a target organ cannot respond?
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
3
Human Systems and Homeostasis
Section 2: Mechanisms of Homeostasis
Name ______________________________ Class ___________________ Date __________________
Study Guide B continued
MAIN IDEA: Negative feedback loops are necessary for homeostasis.
4. Study the following line drawings. Which of the following diagrams
represents negative feedback and which represents positive feedback? Explain
your answer.
A.
B.
_______________________________________________________________
_______________________________________________________________
5. It’s a hot day and you’re sweating. Is this response an example of a positive or
negative feedback loop? Explain your answer.
_______________________________________________________________
_______________________________________________________________
6. When you run, your muscles require more oxygen as their level of activity
increases. Explain briefly how your control systems act to bring more oxygen
into your body.
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_______________________________________________________________
_______________________________________________________________
Vocabulary Check
7. What is the difference between positive and negative feedback loops?
_______________________________________________________________
_______________________________________________________________
8. Think of an analogy that would illustrate the process of feedback for someone
who does not know what the word means.
_______________________________________________________________
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
4
Human Systems and Homeostasis
Section 2: Mechanisms of Homeostasis
Name ______________________________ Class ___________________ Date __________________
Section 3: Interactions Among Systems
Study Guide B
KEY CONCEPT
Systems interact to maintain homeostasis.
VOCABULARY
thermoregulation
MAIN IDEA: Each organ affects other organ systems.
1. The organs in the body work together like members of a pit crew servicing a
race car. What other analogies can you think of to illustrate organ systems
working together?
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
2. Fill in the table below to explain what each organ does to help produce vitamin
D in your body.
Organ
Function
Skin
Liver
Kidneys
3. What role does the hypothalamus play to help regulate body temperature?
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
MAIN IDEA: A disruption of homeostasis can be harmful.
4. List three reasons why homeostasis in the body might be disrupted.
_______________________________________________________________
_______________________________________________________________
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
5
Human Systems and Homeostasis
Section 3: Interactions Among Systems
Name ______________________________ Class ___________________ Date __________________
Study Guide B continued
5. Why is a long-term disruption of homeostasis usually more serious than a
short-term disruption?
_______________________________________________________________
_______________________________________________________________
Fill in the concept map to help you remember what you know about long-term and
short-term disruption of homeostasis.
Disruption of homeostasis
can be
6.
9.
usually leads to
can lead to
10. damage to many organs over
time
7.
example
example
8.
11.
Vocabulary Check
11. Think of a diagram that might illustrate the term thermoregulation for
someone unfamiliar with the word. Use the space below to sketch your
diagram.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
6
Human Systems and Homeostasis
Section 3: Interactions Among Systems