Concept 2 Notes - Cell Transport

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Homeostasis
• The need of an organism to maintain and
regulate constant or stable internal
conditions.
• How does your body regulate (aka maintain
homeostasis)?
– Temperature, pH, and the concentration of other
materials and nutrients must be maintained
within a relatively narrow margin.
• Much of homeostasis is maintained by the
cell membrane controlling movement of
things in and out of the cell
Cell Membrane
• The cell membrane is said to be selectively
permeable, meaning certain substances can
move across it freely, while others must move
through a “gate”.
• Transport of materials can be classified as
either passive transport or active transport.
Cellular Transport
• Passive Transport requires no extra
energy by the cell because molecules move
from high concentration (squished together)
to low concentration (spread out) areas
down the concentration gradient.
• Active Transport requires extra energy
(ATP) to be spent to bring materials into the
cell or expel materials out of the cell moving
from low concentration to high concentration
against the concentration gradient.
Examples of Transport
• Passive Transport
– Diffusion
– Osmosis
– Facilitated
Diffusion
• Active Transport
– Molecular
Pumps
– Exocytosis
– Endocytosis
Words to Know
•
Solute – what gets dissolved (Ex. Lemonade
powder)
•
Solvent – does the dissolving (Ex. Water)
•
Solution – uniform mixture of two or more
substances (Ex. Lemonade)
•
Concentration – amount of solute dissolved
in solvent
•
Symbol for abbreviation = [ ]
Passive Transport:
Diffusion
• The spreading out of molecules across a
membrane until they are equally concentrated
on both sides of the membrane.
• Molecules move down a concentration
gradient, from high [ ] to an area of low [ ]
– Ex. Oxygen and Carbon Dioxide
Over time…
Passive Transport:
Facilitated Diffusion
• A transport protein acts as a protein channel to
help (facilitate) the diffusion of molecules that
normally couldn‘t pass through the cell membrane
• Molecules move down a concentration
gradient, from high [ ] to an area of low [ ]
– Ex. Glucose/sugar, sodium/salt
Over time…
Passive Transport:
Osmosis
• The diffusion of water across the cell
membrane
• Water molecules move down a
concentration gradient, from high [ ] to an
area of low [ ]
Over time…
Passive Transport:
Osmosis
• Hypertonic solutions: water concentration is
below what is found in a cell’s cytoplasm.
– Water will tend to move out of the cell, down its
concentration gradient  Cell shrivels
• Hypotonic solutions: water concentration is above
what is found in a cell’s cytoplasm.
– Water will tend to move into a cell, down its concentration
gradient  Cell swells
• Isotonic solutions: identical water concentrations
to what is found in a cell’s cytoplasm  Cell stays
the same
Passive Transport:
Osmosis
Hypertonic
H 2O
H 2O
Cell shrivels
Hypotonic
Isotonic
H 2O
H2O
H 2O
Cell swells
H2O
Cell stays the
same
Active Transport
• Remember – not all substances can move so
freely into a cell.
• Some molecules have to be pushed “uphill,”
against a concentration gradient.
– This means substances are moving from an area
of low [ ] to an area of high [ ]
• Other substances are too big to move
through a protein channel, and have to be
enveloped by the cell or excreted by the cell.
– This is accomplished by either endocytosis or
exocytosis.
Active Transport:
Molecular Pumps
• When a cell uses energy to pump molecules
across the membrane through a protein channel.
• This allows a cell to concentrate key molecules
within the cell, or remove waste quickly from the
cell.
– Ex. Calcium (Ca2+), potassium (K+), chlorine (Cl-) and
sodium (Na+) = ions (charged particles)
ENERGY
Over time…
Active Transport:
Endocytosis
• A cell uses
energy to import
large amounts of
materials INTO the
cell using a vesicle
• Ex. White blood
cells engulf
bacteria to fight
infection
Active Transport:
Exocytosis
• A cell uses energy to
export large amounts
of materials OUT OF
the cell using a
vesicle
• Ex. Nerve cells
release
neurotransmitters to
pass signals to the
brain
Practice Time!
Type of
Transport
Passive/Acti
ve
Ex. of what is
being moved
Facilitated
Diffusion
How it helps maintain
homeostasis
Regulates blood sugar
Active
Endocytosis
Neurotransmitters
Captures bacteria
Passive
Passive
Controls blood
pressure by regulating
blood volume
O2 and CO2
K+, Na+, Ca2+, Cl-
Muscle contractions
and nerve signal
conduction
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