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KEY CONCEPT
The human body is
complex.
BEFORE, you learned
NOW, you will learn
• All living things are made
of cells
• All living things need energy
• Living things meet their needs
through interactions with the
environment
• About the organization of the
human body
• About different types of tissues
• About the functions of organ
systems
VOCABULARY
THINK ABOUT
tissue p. 586
organ p. 587
organ system p. 588
homeostasis p. 588
How is the human body like a city?
A city is made up of many
parts that perform different
functions. Buildings provide
places to live and work.
Transportation systems move
people around. Electrical
energy provides light and
heat. Similarly, the human
body is made of several systems. The skeletal system, like the framework of a building, provides support. The digestive system works with
the respiratory system to provide energy and materials.
What other systems in your body can you compare to a
system in the city?
The body has cells, tissues, and organs.
MAIN IDEA WEB
As you read this section,
complete the main idea
web begun on page 584.
Your body is made of many parts that work together as a system to
help you grow and stay healthy. The basic level of organization in your
body is the cell. Next come tissues, then individual organs, and then
systems that are made up of organs. The highest level of organization
is the organism itself. You can think of the body as having five levels of
organization: cells, tissues, organs, organ systems, and the organism.
Although these levels seem separate from one another, they all work
together.
Check Your Reading
What are five levels of organization in your body?
Chapter 17: Systems, Support, and Movement 585
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Systems
How do the systems in your body
interact?
SKILL FOCUS
PROCEDURE
MATERIALS
1
Work with other classmates to make a list of everyday activities.
2 Discuss how your body responds to each task. Record your ideas.
3 Identify and count the systems in your body that you think are
Predicting
large sheet of
paper
TIME
20 minutes
used to perform the task.
4 Have someone from your group make a chart of the
different activities.
WHAT DO YOU THINK?
• Which systems did you name, and how did they work together
to perform each activity?
• When you are asleep, what activities does your body perform?
CHALLENGE How could you make an experiment that would
test your predictions?
Cells
The cell is the basic unit of life. Cells make up all living things. Some
organisms, such as bacteria, are made of only a single cell. In these
organisms the single cell performs all of the tasks necessary for survival. That individual cell captures and releases energy, uses materials,
and grows. In more complex organisms, such as humans and many
other animals and plants, cells are specialized. Specialized cells perform specific jobs. A red blood cell, for example, carries oxygen from
the lungs throughout the body.
Tissues
A tissue is a group of similar cells that work together to perform a particular function. Think of a tissue as a brick wall and the cells within it
as the individual bricks. Taken together, the bricks form something
larger and more functional. But just as the bricks need to be placed in a
certain way to form the wall, cells must be organized in a tissue.
Check Your Reading
How are cells related to tissues?
The human body contains several types of tissues. These tissues
are classified into four main groups according to their function:
epithelial tissue, nerve tissue, muscle tissue, and connective tissue.
586 Unit 5: Human Biology
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•
•
•
•
Epithelial (ehp-uh-THEE-lee-uhl) tissue functions as a boundary.
It covers all of the inner and outer surfaces of your body. Each of
your internal organs is covered with a layer of epithelial tissue.
Nerve tissue functions as a messaging system. Cells in nerve
tissue carry electrical impulses between your brain and the
various parts of your body in response to changing conditions.
Muscle tissue functions in movement. Movement results when
muscle cells contract, or shorten, and then relax. In some cases,
such as throwing a ball, you control the movement. In other
cases, such as the beating of your heart, the movement occurs
without conscious control.
Connective tissue functions to hold parts of the body together,
providing support, protection, strength, padding, and insulation.
Tendons and ligaments are connective tissues that hold bones
and muscles together. Bone itself is another connective tissue. It
supports and protects the soft parts of your body.
Organs
Groups of different tissues make up organs. An organ is a structure
that is made up of two or more types of tissue that work together to
carry out a function in the body. For example, the heart that pumps
blood around your body contains all four types of tissues. As in cells
and tissues, the structure of an organ relates to its function. The stomach’s bag-shaped structure and strong muscular walls make it suited for
breaking down food. The walls of the heart are also muscular, allowing
it to function as a pump.
Levels of Organization
The human body can be studied at different levels
of organization.
250 Organism
(human)
Cells
(muscle cells)
Tissue
(cardiac muscle)
Organ
(heart)
Organ system
(circulatory system)
Chapter 17: Systems, Support, and Movement 587
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Organ Systems
An organ system is a group of organs that together perform a function that helps the body meet its needs for energy and materials. For
example, your stomach, mouth, throat, large and small intestines,
liver, and pancreas are all part of the organ system called the digestive
system. The body is made up of many organ systems. In this unit, you
will read about these systems. They include the skeletal, muscular, respiratory, digestive, urinary, circulatory, immune, nervous, and
reproductive systems. Together, these systems allow the human organism to grow, reproduce, and maintain life.
The body’s systems interact
with one another.
reading tip
VOCABULARY
The word homeostasis
contains two word roots.
Homeo comes from a root
meaning “same.” Stasis
comes from a root meaning
“stand still” or “stay.”
The ability of your body to maintain internal
conditions is called homeostasis (HOH-meeoh-STAY-sihs). Your body is constantly
regulating such things as your body temperature, the amount of sugar in your blood, even
your posture. The processes that take place in
your body occur within a particular set of
conditions.
The body’s many levels of organization,
from cells to organ systems, work constantly to
maintain the balance needed for the survival of
the organism. For example, on a hot day, you
may sweat. Sweating keeps the temperature
inside your body constant, even though the
temperature of your surroundings changes.
KEY CONCEPTS
CRITICAL THINKING
1. Draw a diagram that shows
the relationship among cells,
tissues, organs, and organ
systems.
4. Apply How does drinking
water after you sweat help
maintain homeostasis?
2. Make a chart of the four basic
tissue groups that includes
names, functions, and
examples.
3. Identify three functions performed by organ systems.
588 Unit 5: Human Biology
5. Compare and Contrast
Compare and contrast the four
basic tissue groups. How
would all four types of tissue
be involved in a simple activity,
like raising your hand?
INFER This student is
drinking water after
exercising. Why is it
important to drink fluids
after you sweat?
CHALLENGE
6. Apply Describe an object,
such as a car, that can be used
as a model of the human body.
Explain how the parts of the
model relate to the body.