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7-4 The Diversity of Cellular Life
Photo Credit: ©CNSI/Science Photo Library/Photo Researchers, Inc.
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2. Unicellular Organisms
Unicellular organisms are made up of only one cell.
Unicellular organisms dominate life on Earth.
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3. Multicellular Organisms
Organisms that are made up of many cells are called multicellular.
There is a great variety among multicellular organisms.
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4. Multicellular Organisms
Cells throughout an organism can develop in different ways to perform different tasks.
This process is called cell specialization.
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5. Multicellular Organisms
Red blood cells transport oxygen.
Photo Credit: ©Dr. Dennis Kunkle/Phototake
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6. Multicellular Organisms
Cells in the pancreas produce proteins.
Photo Credit: ©Don Fawcett/Photo Researchers, Inc.
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7. Multicellular Organisms
Muscle cells allow movement.
Photo Credit: ©Manford Kage/Peter Arnold, Inc.
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8. Multicellular Organisms
Specialized Plant Cells
Plants exchange carbon dioxide, oxygen, water vapor, and other gases through tiny openings called stomata on the undersides of leaves.
Highly specialized cells, known as guard cells, regulate this exchange.
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9. Multicellular Organisms
Stomata enclosed by guard cells.
Photo Credit: ©Ron Boardman/Getty Images, Inc-Stone
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10. Levels of Organization
The levels of organization in a multicellular organism are:
individual cells
tissues
organs
organ systems
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11. Levels of Organization
Muscle cell
Smooth muscle tissue
Stomach
Digestive system
The levels of organization in a multicellular organism are individual cells, tissues, organs, and organ systems. In this example, muscle cells make up smooth muscle tissue, which, along with other tissues, makes up the stomach, an organ. The stomach, in turn, is part of an organ system, the digestive system.
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12. Levels of Organization
In multicellular organisms, cells are the first level of organization.
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13. Levels of Organization
Tissues
Similar cells are grouped into units called tissues.
A tissue is a group of similar cells that perform a particular function.
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14. Levels of Organization
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15. Levels of Organization
Most animals have four main types of tissue:
muscle
epithelial
nervous
connective
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16. Levels of Organization
Organs 
Organs are groups of tissues that work together to perform a specific function.
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17. Levels of Organization
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18. Levels of Organization
Organ Systems  
In most cases, an organ completes a series of specialized tasks.
A group of organs that work together to perform a specific function is called an organ system.
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19. Levels of Organization
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20. Copyright Pearson Prentice Hall
7-4
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21. Copyright Pearson Prentice Hall
7-4
Cell specialization is characteristic of
bacteria.
all unicellular organisms.
yeasts.
multicellular organisms.
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7-4
Which of the following cells is specialized for contraction?
muscle cell
red blood cell
pancreatic cell
nerve cell
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7-4
The stomach is an example of a(an)
tissue.
organ.
organ system.
organism.
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7-4
Which of the following shows the levels of organization in an organism from the simplest to the most complex?
organ system, organ, cell, tissue
tissue, cell, organ, organ system
cell, tissue, organ, organ system
cell, organ, tissue, organ system
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7-4
Which of the following would probably contain the greatest variety of specialized cells?
an organ system
a tissue
an organ
a multicellular organism
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26. END OF SECTION