The Human Body 9Table 1- 1 The Structural Levels of Organization of the Human Body(^) Structural Level Example
1.. Atoms Atoms are the smallest units of elements,- such as carbon, hydrogen,- and oxygen.
2.. Molecules Molecules are formed when atoms combine through chemical bonds to form units such as
water, sugars, and amino acids.
(^) 3.. Cells Cells are the smallest living units of biologic organization made of structures that perform
(^) the activities of life, such as the nucleus that controls all the activities of the cell.
(^) 4.. Tissues Tissues are made up of similar cells that perform similar functions, such as muscle tissues that
cause contraction and movement.
5.. Organs There are four different kinds of tissues (epithelial, connective, muscle, and nervous) that
group together in different proportions to make an organ like the stomach, which mixes our
food with digestive- enzymes.
6.. Systems A group of organs makes up a body system like the nose, pharynx, larynx, trachea, bronchi,
and lungs that makes up the respiratory system whose function is to bring in oxygen to the
body’s cells and take away carbon dioxide gas.
(^) 7.. Human Organism All of the organ systems together constitute a functioning human being.
Hair
Skin
Fingernails
Toenails
Integumentary system^
Skin and accessory organs such
as hair, nails, sweat glands, and
oil glands.
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Bone
Cartilage
Joint
Skeletal system^
Bones, cartilage, and joints.
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Tendon
Muscular system^
Muscle and tendons.
Skeletal
muscles
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Figure 1- 6 The integumentary, skeletal, and muscular systems of the
body.