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Cell Review
Prokaryotic Cells: these are simple cells that consist
of little more than a cell membrane, some DNA, and
cytoplasm; they do not have a nucleus or any organelles
(membrane-bound structures)
Eukaryotic Cells: these are more complicated cells that
contain a nucleus and organelles
Cell Structures:
Plasma membrane
 also called the cell membrane, this structure surrounds the cell to separate it
from its external environment
 composed of a phospholipid bilayer that has proteins embedded in it
 cholesterol is also an
important component
of cell membranes
since it keeps the
membrane intact yet
fluid
 the membrane acts as
a selective barrier by
allowing only certain
substances to enter
and leave the cell
Cell wall
 tough, rigid outer covering that protects cells and helps them maintain their
shape
 found surrounding the plasma membrane of plant cells, fungi cells, most
bacterial cells, and some protist cells
Nucleus
 manages all the functions of a cell
 this is where the DNA is located
 the nuclear membrane or nuclear envelope functions to
separate the nucleus from the cytoplasm; it contains
pores so that substances may enter or leave the nucleus
 within the nucleus is the nucleolus, a structure within the
nucleus that is responsible for making ribosomes
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Ribosomes
 found attached to the rough endoplasmic reticulum or
suspended in the cytoplasm
 these structures use the information in a RNA strand to
make proteins
Endoplasmic reticulum (ER)
 an extensive network of membranes that is
the site of many chemical reactions
endoplasmic reticulum
 there are 2 types:
with ribosomes
 Rough ER: contains ribosomes that make proteins
 Smooth ER: makes lipids, steroids, and is involved in detoxification;
important in cells that are responsible for ridding the body of toxic
substances (ex: liver)
Cytoplasm
 a semi-fluid substance in which all of the cell’s organelles are suspended
 located between the nucleus and the cell membrane
Golgi apparatus
 also called the Golgi body or the Golgi complex
 series of flat membrane-bound sacs
 packages proteins made from the RER and sends
them in membrane bound vesicles to their
destination
Vacuoles
 membrane-bound compartment that serves many functions (ex: absorbs
water, stores proteins, stores wastes, etc.)
 plant cells have one large central vacuole whereas animal cells contain
several small vacuoles
Lysosomes
 membrane-bound organelle filled with hydrolytic enzymes
 these enzymes are used to break down substances (ex: carbohydrates,
proteins, lipids, old organelles, etc.)
Mitochondria
 structures that break down food molecules and
transform them into energy
 has a highly-folded inner membrane surrounded by
an outer membrane
 the inner membrane is where the energy-storing
molecules are made
Chloroplasts
 found in plant cells and in some protists
 these structures transform light energy into chemical energy and store the
energy as food
 contain chlorophyll, the green pigment that traps sunlight and gives plants
their color
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Cytoskeleton
 made up of tiny rods and filaments that form
a framework for the cell
 provides support and helps maintain the
shape of a cell as well as helping cell parts
to move from place to place within the cell
Cilia
 short, hairlike extensions on the cell membrane used for movement
Flagella
 long, whip-like structures used for movement
Cell Transport:
 small molecules such as water pass freely through the membrane
 large molecules such as proteins and sugars don’t pass freely and must be
transported into the cell
 although ions are small molecules, they do not pass freely through the
membrane because of their charge
 passive transport:
o movement across the cell membrane without the use of energy
o includes diffusion, the movement of molecules from an area of high
concentration to an area of low concentration
o ALWAYS OCCURS DOWN A CONCENTRATION GRADIENT!
o The rate of diffusion depends on temperature and the size of the
molecules
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
types of diffusion:
o Simple—unassisted diffusion of small
particles or lipid-soluble molecules
o Osmosis—unassisted diffusion of
water
o Facilitated diffusion—diffusion with
the help of carrier proteins
 active transport:
o requires energy and a
carrier protein
o movement from an area of
low concentration to an
area of high concentration
 bulk transport:
o requires energy
o there are 2 types of bulk transport:
 exocytosis: substances
move from the cell into
the extracellular space
 endocytosis: substances
move from the
extracellular space into
the cell; there are 2 types
of endocytosis
 phagocytosis—solid is moved into the cell
 pinocytosis—liquid is moved into the cell
Concentrations:
 isotonic
o the concentration of solutes inside the cell is
equal to the concentration of solutes outside
the cell
o there is no net movement of molecules in or
out of the cell
o the cell maintains its normal size and shape
 hypertonic
o the concentration of solutes outside the cell is
higher than inside the cell
o water moves out of the cell
o the cell shrinks
 hypotonic
o the concentration inside the cell is greater than
outside the cell
o water moves into the cell causing it to swell
o if too much water enters the cell, it may burst
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