Sunshine StateSTANDARDSSC.F.1.3.2: The studentknows that the struc-tural basis of mostorganisms is the celland most organisms aresingle cells, while some,including humans, aremulticellular.SC.H.1.3.6: The studentrecognizes the scientificcontributions that aremade by individuals ofdiverse backgrounds,interests, talents, andmotivations.

Chapter 16: Systems, Support, and Movement 571

BEFORE, you learned

• All living things are made of cells

• All living things need energy • Living things meet their needs

through interactions with theenvironment

NOW, you will learn

• About the organization of thehuman body

• About different types of tissues• About the functions of organ

systems

KEY CONCEPT

The human body iscomplex.

The body has cells, tissues, and organs.Your body is made of many parts that work together as a system tohelp you grow and stay healthy. The basic level of organization in yourbody is the cell. Next come tissues, then individual organs, and thensystems that are made up of organs. The highest level of organizationis the organism itself. You can think of the body as having five levels oforganization: cells, tissues, organs, organ systems, and the organism.Although these levels seem separate from one another, they all worktogether.

Check Your Reading What are five levels of organization in your body?

MAIN IDEA WEBAs you read this section,complete the main ideaweb begun on page 570.

THINK ABOUT

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 sys-tems. The skeletal system, like the framework of a build-ing, provides support. The digestive system works withthe respiratory system to provide energy and materials.What other systems in your body can you compare to asystem in the city?

FCAT VOCABULARYtissue p. 572organ p. 573

VOCABULARYorgan system p. 574homeostasis p. 574

572 Unit 5: Human Biology

CellsThe cell is the basic unit of life. Cells make up all living things. Someorganisms, such as bacteria, are made of only a single cell. In theseorganisms the single cell performs all of the tasks necessary for sur-vival. That individual cell captures and releases energy, uses materials,and grows. In more complex organisms, such as humans and manyother animals and plants, cells are specialized. Specialized cells per-form specific jobs. A red blood cell, for example, carries oxygen fromthe lungs throughout the body.

TissuesA is a group of similar cells that work together to perform a par-ticular function. Think of a tissue as a brick wall and the cells within itas the individual bricks. Taken together, the bricks form something larger and more functional. But just as the bricks need to be placed in acertain 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 tissuesare classified into four main groups according to their function:epithelial tissue, nerve tissue, muscle tissue, and connective tissue.

tissue

SystemsSystems

SKILL FOCUSPredicting

MATERIALSlarge sheet of

paper

TIME20 minutes

How do the systems in your body interact?PROCEDURE

Work with other classmates to make a list of everyday activities.

Discuss how your body responds to each task. Record your ideas.

Identify and count the systems in your body that you think are used to perform the task.

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?

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3

2

1

reminder

Notice that humans havecells, tissues, organs, andorgan systems like those ofmulticellular organisms thatyou studied in grade 6.

Content ReviewFLORIDA

• Epithelial (ehp-uh-THEE-lee-uhl) tissue functions as a boundary.It covers all of the inner and outer surfaces of your body. Each ofyour 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 whenmuscle cells contract, or shorten, and then relax. In some cases,such as throwing a ball, you control the movement. In othercases, such as the beating of your heart, the movement occurswithout 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 bonesand muscles together. Bone itself is another connective tissue. Itsupports and protects the soft parts of your body.

OrgansGroups of different tissues make up organs. An is a structurethat is made up of two or more types of tissue that work together tocarry out a function in the body. For example, the heart that pumpsblood around your body contains all four types of tissues. As in cellsand tissues, the structure of an organ relates to its function. The stom-ach’s bag-shaped structure and strong muscular walls make it suited forbreaking down food. The walls of the heart are also muscular, allowingit to function as a pump.

organ

Chapter 16: Systems, Support, and Movement 573

The human body can be studied at different levels of organization.

Levels of Organization

Tissue(cardiac muscle)

Organ(heart)

Organ system(circulatory system)

Cells(muscle cells)

Organism(human)

250 �

Organ SystemsAn is a group of organs that together perform a func-tion that helps the body meet its needs for energy and materials. Forexample, your stomach, mouth, throat, large and small intestines,liver, and pancreas are all part of the organ system called the digestivesystem. The body is made up of many organ systems. In this unit, youwill read about these systems. They include the skeletal, muscular, res-piratory, digestive, urinary, circulatory, immune, nervous, andreproductive systems. Together, these systems allow the human organ-ism to grow, reproduce, and maintain life.

The body’s systems interactwith one another.

The ability of your body to maintain internalconditions is called (HOH-mee-oh-STAY-sihs). Your body is constantlyregulating such things as your body tempera-ture, the amount of sugar in your blood, evenyour posture. The processes that take place inyour body occur within a particular set ofconditions.

The body’s many levels of organization,from cells to organ systems, work constantly tomaintain the balance needed for the survival ofthe organism. For example, on a hot day, youmay sweat. Sweating keeps the temperatureinside your body constant, even though the temperature of your surroundings changes.

homeostasis

organ system

KEY CONCEPTS1. Draw a diagram that shows

the relationship among cells,tissues, organs, and organ systems.

2. Make a chart of the four basictissue groups that includesnames, functions, and examples.

3. Identify three functions per-formed by organ systems.

CRITICAL THINKING4. Apply How does drinking

water after you sweat helpmaintain homeostasis?

5. Compare and ContrastCompare and contrast the fourbasic tissue groups. Howwould all four types of tissuebe involved in a simple activity,like raising your hand?

CHALLENGE6. Apply Describe an object,

such as a car, that can be usedas a model of the human body.Explain how the parts of themodel relate to the body.

574 Unit 5: Human Biology

INFER This student isdrinking water afterexercising. Why is itimportant to drink fluidsafter you sweat?

reading tip

The word homeostasiscontains two word roots.Homeo comes from a rootmeaning “same.” Stasiscomes from a root meaning“stand still” or “stay.”