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CELL THEORY AND STRUCTURE
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All living things are made of cells
Cells are the basic unit of structure and function
in an organism (basic unit of life)
Cells come from the reproduction of existing cells
(cell division)
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In 1665,Hooke is responsible for naming cells
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In 1673, Leeuwenhoek was first to view living organisms in
pond water
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In 1838, Schleiden concluded that all plants were made of
cells
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In 1839, Schwann concluded that all animals were made of
cells
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In 1855, Virchow observed, under the microscope, cells
dividing and reasoned that all cells come from other preexisting cells by cell division
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In 1970,Lynn Margulis, provided evidence that some
organelles within cells were at one time free living cells
themselves – this is called Endosymbiotic Theory
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Chloroplasts and mitochondria were the organelles she
pointed to as evidence of this theory
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Chloroplast and Mitochondria have their own DNA which is
different from the DNA of the cell
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Unicellular – composed
of one cell
Ex: bacteria, yeast
• Multicellular - composed
of many cells that may
organize
Ex: butterfly, flower
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• Have a nucleoid
region contains the
DNA (no nucleus)
• Have a cell
membrane & cell
wall
• Contain ribosomes
to make proteins in
their cytoplasm
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Contain 3 basic cell
structures:
 Nucleus (containing
DNA)
 Cell Membrane
 Cytoplasm with
organelles
 Organelles have
specific functions
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Plant Cell
Animal Cell
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 Contain
digestive
enzymes
 Use Active Transport to
trap and break down
food an worn out cell
parts
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 Inside
nucleus
 Produces
the
ribosomes that make
proteins
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• Smooth ER - lacks
ribosomes &
detoxifies poisons
and synthesizes
lipids
• Rough ER - has
ribosomes on its
surface & makes
proteins to EXPORT
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• Site of Cellular
respiration – the
capturing of
energy from food
• Breaks down
glucose to
produce energy
ATP
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Chloroplast
• Process called
photosynthesis
occurs here
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Cell wall
• Made of cellulose
• Found in plant cells
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Vacuole
Have a large central
vacuole
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• Glycogen is
stored in the
cytoplasm of
animal cells for
food energy
glycogen
granule
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Near
the nucleus in an
animal cell
Help cell divide
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Animal cells
Plant cells
Relatively small in
size
Relatively large in
size
Irregular shape
Regular shape
No cell wall
Cell wall present
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Animal cells
Plant cells
Vacuole small or
absent
Large central vacuole
Glycogen as food
storage
Starch as food
storage
Nucleus at the center
Nucleus near cell wall
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Composed of double layer of phospholipids and proteins
Controls what enters or leaves the cell
Surrounds outside of ALL cells
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
channel
Lipid bilayer
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The cell membranes of all cells are selectively permeable
This means that some materials can pass easily through
the membrane
Examples: H20, CO2 and O2
This also means that some materials cannot pass easily
through the membrane
Examples: glucose and salts
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Proteins help move large molecules or aid in cell recognition
Peripheral proteins are attached on the surface (inner or
outer)
Integral proteins are embedded completely through the
membrane
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Provide a binding site for enzymes
Interlocking surfaces bind cells together (junctions)
Contains the cytoplasm (fluid in cell)
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Phospholipid bilayer makes up the cell membrane
 Contains a polar head (attracts H2O) and 2 non-polar fatty
acid tails (repels H2O)
How is a phospholipid different from a triglyceride?
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Fluid: individual phospholipids and proteins can move
side-to-side within the layer, like a liquid.
Mosaic: the pattern produced by the scattered
proteins on the surface of the cell when the
membrane is viewed from above.
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Materials that are soluble in lipids can pass through the cell
membrane easily
Ex: Oxygen, carbon dioxide, and water
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Passive Transport
 Does not require
cellular energy
 Types:
1. Simple
Diffusion
2. Osmosis
3. Facilitated
Diffusion
Active Transport
 Does require
cellular energy
 Types:
1. Membrane
Pumps
2. Endocytosis
3. Exocytosis
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 Movement
of materials from a region of high
concentration to a region of low concentration
 Materials are moving down/with
their concentration gradient
 Example:
Oxygen diffusing
into a cell and carbon dioxide
diffusing out using kinetic
energy
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Osmosis is the passive transport (diffusion) of water across
a membrane
Moves from a region of HIGH water potential (low solute) to
a region of LOW water potential (high solute)
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The purpose of osmosis is to
balance out the concentration of
materials between the
environment inside of the cell and
the environment outside the cell
Water moves because the other
materials cannot
This allows the cell to be in
equilibrium - balance
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Solution - a liquid mixture in which the minor component
(the solute) is uniformly distributed within the major
component (the solvent).
Examples – salt water or glucose solutions; solutes are salt
or glucose, solvent is water
Types of solutions:
Isotonic
Hypotonic
Hypertonic
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10% NaCL
90% H2O
ENVIRONMENT
CELL
10% NaCL
90% H2O
Q: What is the
direction of water
A: No net movement (water molecules
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movement in an isotonic
10% NaCL
90% H2O
ENVIRONMENT
CELL
20% NaCL
80% H2O
Q: What is the
direction of water
A: Water
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15% NaCL
85% H2O
ENVIRONMENT
CELL
5% NaCL
95% H2O
Q: What is the
direction of water
A: Water moves
out ofinthe
movement
a cell.
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Hypotonic solution will result in
cytolysis – cell bursts from build up
of water inside cell
Hypertonic solution will result in
plasmolysis – cell membrane pulls
away from the cell wall in plant,
fungal or bacterial cells
Plant cells prefer a hypotonic
environment
Animal cells prefer an isotonic
environment
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Uses transport
proteins to move
materials from high to
low concentration
Examples: Glucose or
amino acids moving
from blood stream into
a cell.
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Types of Membrane Proteins:
Structural
Cell recognition
Communication
Transport:
a.
b.
Channel proteins are embedded in the cell membrane & have
a pore for materials to cross
Carrier proteins can change shape to move material from
one side of the membrane to the other
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Channel proteins
act
as bridges to allow
materials to pass
across
the membrane
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Some Carrier
proteins do not
extend through the
membrane.
They bond and drag
molecules through the
lipid bilayer
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Cells need a steady supply of sodium (Na+), potassium (K+),
calcium (Ca2+) and hydrogen (H+) in order to function
correctly
Protein pumps that span the cell membrane are powered by
ATP and supply these materials to the cell on demand
This requires a steady supply of ATP
Materials are moving from and area of low concentration to
an area of high concentration
They are moving up/against their concentration gradient
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3 Na+ pumped out for every 2 K+ pumped in
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Q: What is a vesicle?
A: A small bubble within a cell surrounded in its own lipid
bilayer.
Q: What is the function of a vesicle?
A: Vesicles are involved in:
• Metabolism
• Transport of materials
• Enzyme storage
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Types of active transport using vesicles:
• Exocytosis
• Endocytosis
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Exocytosis -using a vesicle to move big
stuff out of the cell
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How it works:
Vesicle is formed around some sort of material made by
the cell (like proteins or hormones)
Vesicle is released and travels toward cell membrane
Vesicle fuses with cell membrane
Vesicle expels materials to the outside of the cell
membrane
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Large amount of materials move into the cell by one
of two forms of endocytosis:
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Pinocytosis  Materials dissolve in water to be brought into cell
 Called “Cell Drinking”
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Phagocytosis - Used to engulf large particles such as food,
bacteria, etc. into vesicles.
 Called “Cell Eating”
 White blood cells eat foreign substances in your body this way
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Pinocytosis
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