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Chapter 3:
Cells
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• In 1665, An English Scientist Robert Hooke used a 3 lens
microscope to examine thin slices of cork.
• Hooke noticed the cork was made of many tiny
compartments.
• These compartments reminded Hooke of the small
rooms at his monastery.
• These rooms were called cells - so he termed these small
openings cells.
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•Soon after, a man named Anton
Van Leeuwenhoek, came up with a
very powerful single-lens
microscope.
•Leeuwenhoek became one of the
first people to describe living cells
when he observed microscopic
organisms swimming in pond
water.
•Microscopes got better and better
over the next century which led to
more scientist studying cells.
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•German scientist Matthias Schleiden- studied plant tissue
and concluded that plants are made of cells.
•German scientist Theodor Schwann- studied animal
tissue and concluded that animals are mad of cells.
•German scientist Rudolph Virchow- concluded that all
cells come from pre-existing cells.
•All of these findings led to one unified concept called the
Cell Theory
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THE CELL THEORY STATES:
1. All organisms are made of cells.
2. Cells are the basic unit of life.
3. Cells come form pre-existing cells.
•The variety of cell types is enormous. Cells come in many
different shapes, sizes, and functions.
•While there are many differences, all cells share some
basic common characteristic:
•All cells have a cell membrane and cytoplasm.
•Cell membrane= outer boundary
•Cytoplasm= jellylike substance inside membrane
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There are 2 general types of cells:
1. Prokaryotic Cells
2. Eukaryotic Cells
E. coli
Prokaryotic Cells•Do not contain a nucleus or other membrane bound
organelles.
•The cell’s DNA floats in the cytoplasm.
•Most prokaryotes are microscopic single-celled
organisms.
Bacteria are an example of
prokaryotic cells.
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Plant and animals are eukaryotic
organisms
•Eukaryotic Cells:
•Have a nucleus and other membrane bound
organelles.
•The nucleus is the largest of the organelles and
is the control center of the cell.
•It contains the genetic information for the
cell.
•Eukaryotes may be multicellular or single-celled
organisms.
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•Eukaryotic Cells:
•Eukaryotic cells are highly organized.
They contain many membrane bound
organelles that help the cell carry out
day to day functions.
•Most organelles are held in place by a
cytoskeleton, which is a network of
proteins that maintains the cell shape
and strength.
•The Cytoplasm also plays a key role in
cell structure.
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Cell Organelles:
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The Nucleus:
• Stores most all of the cells
genetic information.
• It is known as the control center
of the cell.
• The nucleus must:
– Protect DNA
– Make DNA available for
duplication
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The Nucleus:
• Molecules must be able to enter and leave the
nucleus, so the nuclear membrane has pores in it to
allow certain molecules in and out.
• Inside the nucleus you will find:
– Nucleolus-this is a region where tiny organelles
responsible for making proteins are produced.
– These specialized protein making organelles are
called ribosomes.
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Endoplasmic Reticulum:
• This organelle usually takes up a lot of the
space of the cytoplasm.
• The “E.R.” is an interconnected network of
thin folded membrane.
• They makeup of the E.R. is similar to that of
the cell membrane.
• The E.R. itself is usually larger than the cell
itself, but it has so many folds that it fits easily.
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Endoplasmic Reticulum:
• The E.R.’s major function is
the production of proteins
and lipids.
• There are two types of E.R.
– Rough E.R.- has ribosomes
attached to surface
– Smooth E.R.- has no ribosomes
attached to surface
• Both rough and smooth E.R.
perform the same functions;
however, rough E.R. does have
more of a protein synthesis
function.
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Ribosomes:
• Small vesicles that are responsible for making
proteins.
• Ribosomes take amino acids and chain them
together to make many different proteins.
• Ribosomes themselves are made of proteins and
RNA.
• Ribosomes are made at the nucleolus and are
then sent to the cytoplasm.
• They are either free-floating or attached to the
endoplasmic reticulum.
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Golgi Apparatus:
• This is an organelle
that is made up of a
stack of closely layered
membranes.
• The Golgi’s function is
to process, sort, and
deliver proteins.
• The membranes
contain enzymes that
further modify
protein.
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Vesicles:
• There are many different types of vesicles.
These are structures that take materials from
the rest of the cytoplasm and transport them
from place to place within the cell.
• Vesicles are short-lived organelles and are
replaced by the cell on a consistent basis.
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Mitochondria:
• Are known as the power house of
the cell.
• These are two-membrane
structures.
– The inner membrane has many folds
that increase its surface area.
• This increased surface area allows for
more area to create energy
• Mitochondria has its own DNA and
ribosomes which would suggest they
were once independent living
organisms.
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Vacuoles:
• These are fluid-filled sacks used for storage of
materials needed by the cell.
• These materials may include water, food
molecules, ions, and enzymes.
• Vacuoles are different in plant and animal
cells!
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Vacuoles:
• In animal cells there are many vacuoles that
are smaller in size.
• All do the storage function!
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Vacuoles:
• In plant cells, there is usually only one vacuole
that is centrally located and takes up most of the
space of the cell.
• It still performs the storage function, but it also
has a structure function!
• When the vacuole is full, it exerts pressure
against the cell membrane and gives the plant
structure.
• When the vacuole loses water during a drought,
plants wilt.
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Plant Cell Vacuoles
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Lysosomes:
• These are membrane bound organelles that
contain enzymes.
• They are known as the “clean-up crews” of the
cell.
• Lysosomes break down damaged or worn out
cell parts.
• They also protect the cell from invading bacteria
and viruses.
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Lysosomes:
• Lysosomes are numerous in animal cells, but
are questioned in plant cells.
• Most scientists believe that plant cells do not
contain Lysosomes, but others believe they
do.
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Centrosome and Centrioles:
• The centrosome is an area that
contains centrioles.
• Centrioles only occur in animal
cells!
• These cylinder shaped organelles
are made of microtubule
filaments.
• Centrioles organize the filaments
in the cytoskeleton before the
cell divides.
• Centrioles are not found in
plants, so scientists believe they
are not essential to cell division.
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Cell Wall:
• ONLY FOUND IN PLANT CELLS AND SOME
ALGAE AND FUNGI.
• The cell wall is a rigid layer that gives
protection, support, and shape to the cell.
• The cell wall is outside the cell membrane.
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Chloroplasts:
• Are organelles that carry out
photosynthesis for plants and
some algae.
• Photosynthesis creates energy
for the cell by taking sunlight
and turning it into chemical
energy.
• Like mitochondria, chloroplasts
have their own DNA and
ribosomes.
– Both chloroplasts and
mitochondria are found in plant
cells and both are used to create
energy.
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Cell Membrane:
• Cell membranes are composed of 2
phospholipid layers.
• It forms the boundary between the cell and
the outside environment .
• The cell membrane is made of the phosphorus
and lipids.
• The phosphate part is polar!
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Cell Membrane:
• The lipid interior of the cell membrane is nonpolar.
– So, the outside layers of a membrane are polar
and the inside are non-polar.
– This system allows certain things to enter and
leave the cell.
• The cell membrane is made up of many
different other structures.
– Lipids, carbohydrates, and proteins also make up
the membrane.
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Cell Membrane:
• Because the membrane is made up of so many
different things it is said to be a “Fluid Mosaic
Model”.
– This means the membrane is not rigid, but rather
flexible. Also mosaic means made of many
different things.
• It is also said the membrane is “selectively
permeable”
– What does that mean?
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Cell Membrane:
• Cell membranes are called “selectively
permeable” because they only allow certain
materials in and out of the cell.
• The cell must be able to maintain homeostasis
(or a constant internal body environment).
– In order to do this, the cell must control what
enters and leaves the cell.
• How do molecules enter and exit the cell?
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Cell Membrane:
• To get in and out of the cell molecules can do
one of two things:
– Pass through pores
– Use helpful proteins within the cell membrane.
• Size and polarity are the 2 main factors that
determine what enters and leaves the cell.
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Osmosis and Diffusion:
• Cells are constantly importing and exporting
substances in and out of the cell.
• Some of these functions require energy while
others do not
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Osmosis and Diffusion:
• Passive Transport– Is the movement of molecules across a membrane
with NO ENERGY required from the cell
– These processes are:
• Diffusion
• Osmosis
• Facilitated Diffusion
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Osmosis and Diffusion:
• Active Transport– REQUIRES ENERGY expenditure from the cell.
– These processes are:
• Endocytosis
• Exocytosis
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Passive Transport:
• Passive transport requires no energy because
material are moving down a concentration
gradient, from an area of high concentration
to an area of low concentration (like going
down a hill).
High Concentration
Low Concentration
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Passive Transport:
• Diffusion– Movement of materials from an area of high
concentration to an area of low concentration
down a concentration gradient.
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Passive Transport:
• Osmosis– Movement of water from an area of high
concentration to an area of low concentration.
– Osmosis and diffusion move in opposite directions
– If the concentration of “other” materials is high,
than the water concentration is low and vice
versa.
• This creates 3 types of solutions
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Passive Transport:
• Isotonic Solution- concentrations are equal on
both sides of a cell membrane. Water will
move, but at an equal rate into and out of the
cell
– The cell remains the same
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Passive Transport:
• Hypertonic Solution- water concentration is
higher in the cell…..water will move out of a
cell.
– The cell shrinks
• Hypotonic Solution- water concentration is
higher outside the cell…..water will move into
the cell
– The cell will burst
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Passive Transport:
• Facilitated Diffusion– Some molecules can
pass with no energy
needed, but need a
little direction.
– In facilitated diffusion,
transport proteins
“direct” certain
substances across the
cell membrane.
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Active Transport:
• Sometimes the cell needs materials it already
has a lot of. So in order to get more of what it
needs, it must “spend” energy to move
materials against the gradient (up the hill).
• This is called active transport. Active transport
uses energy and transports proteins to get
materials in the cell
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Active Transport:
• There are 2 general types of active transport:
– Endocytosis• Taking materials into the cell by manipulating the cell
membrane.
• Particles enter without actually ever crossing the cell
membrane.
– Exocytosis• The exact opposite of endocytosis.
• Particles exit the cell without actually ever crossing the
cell membrane.
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Endocytosis
Exocytosis
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