Cells Have
Distinct Parts
LEARNING OBJECTIVES
1.
Describe
the structure and function of the
plasma membrane.
2.
Identify
the organelles that make up the
cytoplasm of the cell and define the func-
tion of each.
3.
Explain
the role of the nucleus.
T
here are over 100 trillion cells in your
body, each one a distinct structural and
functional unit. There are about 200
different cell types, in many sizes and
shapes. All cells come from other cells through a
process called cell division. With the exception of
red blood cells, all the cells in your body consist of
three major portions (Figure 3.1):
The
plasma
membrane
, or cell membrane,
separates the inside from the outside.
The
cytoplasm
contains
organelles
.
The
nucleus
controls the cell’s activities.
Let’s take a closer look at the structures within
the cell and their functions.
plasma membrane
The outer, limiting
membrane that sepa-
rates a cell's internal
parts from extracellu-
lar fluid or the external
environment.
cytoplasm
(ST-to-
plazm) The fluid inside
a cell and various
internal membrane-
bound compartments.
organelle
(or-gan-EL)
A membrane-bound
structure within a
cell that carries out
specific functions.
nucleus
(NOO-kle-us)
The largest organelle,
which houses the
genetic material and
controls the cell's
activities.
InSight
T h e an im al ce ll
Figure 3.1
The cell is a complex organization with specific
parts that carry out specialized functions.
Flagellum:
A "whip-like" tail that
moves the entire cell and
is present only in some
cells (such as sperm).
Proteasome
Cilia: ----------------------------------------------------------
"Hair-like" projections from the cell membrane
that move material along the cell's surface and
are present only in some cells (such as cells of
the respiratory tract lining).
Centrosome: ----------------
An array of microtubules
(centriole pairs) and
proteins that serves as an
anchor for microtubules
and microfilaments during
cell division.
Cytosol:
'
The fluid inside the
cell where most of
the chemical
reactions occur.
Peroxisome
X
Lysosome:
\ The "stomach" of the cell,
where ingested material
.
(vesicles, foreign cells,
extracellular material) and
worn-out organelles are
digested.
Smooth endoplasmic
reticulum (SER):
A membrane system that
makes fatty acids and
steroids, detoxifies drugs,
and stores calcium ions for
intracellular signaling.
50 CHAPTER 3
Cells and Tissues
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