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Cell Features
Section 3.2
The Cell Theory
The Cell Theory has three parts:
1. All living things are made of one or more cells.
2. Cells are the basic units of structure and function
in organisms.
3. All cells arise from existing cells.
The Cell Theory, continued
Cell Size
Small cells function more efficiently than large cells. If a
cell’s surface area–to-volume ratio is too low, substances
cannot enter and leave the cell well enough to meet the
cell’s needs.
The Cell Theory, continued
Common Cell Features:
outer boundary called the cell membrane
interior substance called cytoplasm
structural support called the cytoskeleton
genetic material in the form of DNA
cellular structures that make proteins,
called ribosomes
Prokaryotes
Prokaryotes are singlecelled organisms that lack
a nucleus and other
internal compartments.
They have a cell wall, may
have cilia or flagella, and
have a single circular
molecule of DNA.
Bacteria are prokaryotes
Eukaryotic Cells
Eukaryotes have:
 A nucleus which
contains the cell’s
DNA
 Other internal
compartments called
organelles.
 Animals are
eukaryotes
Eukaryotic Cells, continued
 The cytoskeleton provides the framework of a
cell.
 There are three basic kinds of fibers:
1. Microfilaments: long slender filaments made of
the protein actin
2. Microtubules: hollow tubes made of the protein
tubulin.
3. Intermediate fibers: thick ropes made of
protein.
Eukaryotic Cells, continued
The cytoskeleton’s
network of protein
fibers anchors the
cell’s organelles and
other components of
the cytoplasm.
The Cell Membrane
 The cell membrane is a selectively permeable
barrier that determines which substances enter
and leave the cell.
 This is caused by the way phospholipids in the
membrane interact with water.
 A phospholipid is a lipid made of a phosphate
group and two fatty acids.
The Cell Membrane, continued
Cell membranes are made of a phospholipid
bilayer
The Cell Membrane, continued