Introduction to Cell Theory
History of Scientists:
1655: Robert Hooke coins the term "cell"
to describe chambers in cork
1674:
Anton Von Leeuwenhoek perfects
techniques for grinding microscope lens
to make the first microscope
1838: Mathais Schleiden concluded that
plants are composed of cells
1839: Theodore Schwann concluded that
animals are composed of cells
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Robert
Hooke- cork
under a
microscope
“cells”
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Anton Von
Leeuwenhoek
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Cell Theory
Those early scientists did experiments on
living things and developed CELL THEORY
Main Ideas of Cell Theory
1) All living things are made of one or more
cells
2) Cells are the basic units of structure &
function of living things
3) All cells come from existing cells
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What are cells made of?
Cells are mostly water. The rest of the
present molecules are:
•protein
•nucleic acid
•carbohydrate
•lipid
•other
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What are cells made of?
By elements, a cell is composed of:
• 60% hydrogen
• 25% oxygen
• 10% carbon
• 5%
nitrogen
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Rules of Diffusion & Osmosis
All substances that enter or leave a cell
must cross its surface
 Small cells function better than large
cells
 WHY? … because substances do not have
to travel as far to reach the center of small
cells
 So, the larger the cell…the longer it takes
to cross it
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2 types of cells
• Eukaryotic
– Organells with
membranes
– Nucleus
– Plant/Animal
– Complex
• Prokaryotic
– No organelles with
membranes
– No nucleus, DNA floats
freely in cell
– Bacteria
– Simple
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-nucleus
-cytoplasm
-nucleolus
-cytoskeleton
-cell membrane
-vacuole
-mitochondria
-chloroplast
-golgi Apparatus
-centrioles
-lysosomes
-ribosomes
-endoplasmic reticulum(ER)
*Rough ER & Smooth ER
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Nucleus
The “brain” of the cell
Controls all of the
cellular activities
DNA is inside the nucleus
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Nucleus
CHROMOSOMES- are found inside
the nucleus
carry the information that
Chromosomes – determines what traits a
living thing will have
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DNA - Deoxyribonucleic acid
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NUCLEOLUS
The dark area in
the nucleus
Like a tiny
nucleus inside the
nucleus.
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CELL MEMBRANE
 Selectively Permeable
 keeps all of the pieces (like the organelles
and the cytoplasm) inside the cell
 controls what goes in and out of the cell
Example: like a big plastic bag with tiny
holes in it (lab)
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How does the cell membrane work?
Has 2 layers of MOLECULES = LipidBILAYER
The layers are made up of molecules called
phospholipids
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Cell Membrane: PHOSPHOLIPIDS
Each phospholipids
has a HYDROPHOBIC
and HYDROPHILIC
end
•HYDRO = means water
•PHOBIC = means afraid
•PHILIC = means loving
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Cell Membrane: PHOSPHOLIPIDS
 One end of the molecule is “afraid” of
the water and one end “loves” being in the
water.
 Proteins are stuck inside the membrane
 Proteins are across the bilayer and
make the holes that let ions and molecules
in and out of the cell
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Mitochondria
 Mito = Mighty / Power
 The Power-House of the cell
 They break down food molecules so the
cell has the energy (ATP) to live
 If a cell needs a lot of energy…it will have
more mitochondria-Ex. Muscle Cells
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Endoplasmic Reticulum
 also known as the “ER”
 it is an organelle inside the cell that is
Responsible for transport INSIDE the cell
There are two different
Smooth ER
Rough ER
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Smooth ER
 Main function is to collect, maintain &
transport proteins and necessary substances
throughout the cell

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Rough ER
It has bumps all over it giving it a “rough”
appearance
Bumps are called RIBOSOMES
ER collects the proteins (built by the
ribosomes) and creates a bubble around them
(packages them)
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MOVEMENT of VESICLES
(prodcut of the cell)
Usually proteins!!!
1) If the cell product goes to the cell
membrane, it will leave through exocytosis
2) If the cell product goes to the golgi
complex, it needs finishing touches before
it can leave or go back into the cell to
perform another function
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GOLGI APPARATUS
•Also called the Golgi Complex
•It is made up of a stack of flattened out sacs
…like a loose stack of pancakes
WHAT DOES IT DO?
1) it takes simple molecules and combines them to
make larger molecules. Adds finishing touches onto
a cellular product
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LYSOSOMES (primarily animal)
•The lysosomes will break down food or toxins that
are in the cell
•There are digestive enzymes in the lysosomes as
well as acids to break down materials
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CYTOPLASM
Cytoplasm- everything inside the cell membrane &
outside of the nucleus. Jelly like fluid that
nourishes the cell
Can also be called the Cytosol
– Mostly H2O
– Contains salts, dissolved gasses & nutrients
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CYTOPLASM
cytoplasm
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CYTOSKELETON
• Chief functions include:
– maintaining the shape of the cell
– keeping the cell from getting smashed
– Keeping organelles in place
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Microtubuole: Attaches to
organelles to keep them in place
Microfilaments
-keep cell from
being
squashed!
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VACUOLE
• Vacuoles are “bubbles” that float in the
cell, hold food and water
• Vacuoles are more important to the
survival of plant cells than they are to
animal cells
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You will know that a plant's vacuoles are
shrinking when you see the plant begin to
droop over
HOLDING UP THE WALLS
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Turgor Pressure- force exerted by the water
entering (osmosis) the vacuole, which then
swells exerting internal force on the cell wall
•Causes “rigidity” so the plant my increase
by stacking cells
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Chloroplast
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Chloroplast
•the site of photosynthesis in eukaryotic
cells
•disk-like structures
•composed of a single membrane
surrounding a fluid containing stacks of
membranous disks
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•SOLAR energy
radiated from the
sun is captured by
plants(chloroplast)
Chloroplast
•Then it is
instantaneously
changed into
ELECTRICAL
energy
•Then packaged as
CHEMICAL energy
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Chloroplast
•photosynthesis takes place inside the chloroplast
the process in which plant use
Photosynthesis- water, carbon dioxide, and energy
form the sun to make food
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Ribosomes
•small dot-like structures in cells
•they are often associated with forming
rough ER
•Ribosomes are the site of protein synthesis
in cells (where proteins are made)
•A ribosome can make the average protein in
about one minute
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Animal Cell
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