a. Cell Membrane. This membrane surrounds and separates the cell from its
environment. It encloses the cytoplasm. The cell membrane also allows certain
materials to pass through it as they enter or leave the cell. It is through the cell
membrane that all materials essential to metabolism are received. All products of
metabolism are disposed of through the cell membrane. The bloodstream and tissue
fluid circulate around the cells and transport the materials to and from these cells.
b. Nucleus. This controls all activities of the cell, including growth and
reproduction. Information is stored in the nucleus and distributed to guide the life
processes of the cell. Cells reproduce to replace worn-out cells, to build new tissues,
and to bring about the growth of the body.
c. Cytoplasm. This is a semifluid material found inside the cell, but outside the
nucleus. Cytoplasm is enclosed by the cell membrane. It is responsible for most of the
chemical activities of the cell.
A tissue is a group of similarly-specialized cells working together to perform a
particular function. The four main types of tissues are epithelial, connective, muscle,
a. Epithelial. Epithelial tissue covers inner and outer surface of the body. It
serves as a lining for vessels and other small cavities inside the body and as skin
outside the body.
b. Connective. Connective tissues are distributed throughout the body to hold
tissues together, to support other tissues, and to fill spaces.
c. Muscle. There are three specialized types of muscular tissue found in the
body--striated (arms and legs), smooth (blood vessels), and cardiac (heart). Muscular
tissue has the ability to contract (shorten), thus producing movement.
d. Nerve. Nerve tissue receives and transmits electrical impulses (messages).
An organ is a structure that is a somewhat independent part of the body and is
composed of several different tissues. Each organ performs a specialized function or
functions. The body has many organs.
The organs of the body are arranged into nine major systems. Each system has
a specific function to perform. All systems are interdependent.