section 4-1 what is homeostasis? cells maintain homeostasis by controlling the movement of...
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CELLS AND THEIR ENVIRONMENT
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PASSIVE TRANSPORT
Section 4-1
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REVIEW What is homeostasis? Cells maintain homeostasis by
controlling the movement of substances across the cell membrane
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RANDOM MOTION AND CONCENTRATION Passive transport is movement
across the cell membrane that does not require energy
Substances travel from areas of high concentration to areas of low concentration
The difference in the concentration of a substance across the space is the concentration gradient
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An substance of high concentration will move into a lower concentration until it is in equilibrium or equal
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MOVEMENT OF SUBSTANCES Particles of a substance will move
randomly If there is a concentration gradient
(uneven concentration) then diffusion occurs
Diffusion is the movement of a substance from an area of high concentration to low caused by the random movement of particles
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MOVEMENT OF SUBSTANCES CONT… Many molecules and ions dissolve in
the cytoplasm and outside of the cell The concentration of substances is
different inside and outside of the cell Molecules will diffuse, to equalize,
and need to pass through the cell membrane
Selectively permeable
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MOVEMENT OF SUBSTANCES CONT… The diffusion of molecules across the
cell membrane is the simplest type of passive transport
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WATER DIFFUSES IN AND OUT Water molecules are small and can
diffuse through the cell membrane easily
Osmosis is the diffusion of water molecules through a selectively permeable membrane
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OSMOSIS Osmosis is a form of passive
transport 3 possibilities of water movement
1. Water moves out2. Water moves in3. No net movement
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WATER MOVES OUT When water diffuses out of the cell,
the cell shrinks A solution that causes a cell to shrink
is hypertonic (too much water goes out)
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WATER MOVES IN When water moves into the cell, the
cell swells A solution that causes a cell to swell
because of osmosis is hypotonic Too much water goes in
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NO WATER MOVES If the outside and inside of the cell have
the same concentration of water molecules, then water diffuses in and out at the same rateNo net movement
A solution that produces no change is isotonic
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PROTEINS HELP TRANSPORT SUBSTANCES Transport proteins provide
passageways for polar molecules and ions to pass through the cell membrane
Each channel only allows a certain substance through
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DIFFUSION THROUGH ION CHANNELS Sodium Na+, Potassium K+, Ca 2+ and
chlorine Cl-, are important in cell functions
Ion channels are a doughnut shaped transport protein for ions like Na+ to pass through
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DIFFUSION THROUGH ION CHANNELS Some pores are always open, others
are closed by gates The rate of movement of a substance
across the membrane is determined by the concentration gradient
An ions movement across the membrane is determined by its charge
The inside of a cell is usually negative
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FACILITATED DIFFUSION Carrier proteins carry specific
substances across the membrane They carry substances down their
concentration gradient Facilitated diffusion uses no energy
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FACILITATED DIFFUSION
Step 1: molecule outside of cell binds to carrier protein
Step 2: carrier protein transports molecule across membrane
Step 3: molecule is released in the cell
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ACTIVE TRANSPORT
Section 4.2
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ACTIVE TRANSPORT Cells must transport certain amino acids,
sugars, and other substance from the cytoplasm to surrounding fluids
Low concentration to high concentration The concentration gradient will cause those
substances to move back into the cell The transport of a substance across a
membrane against its concentration gradient is active transport
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SODIUM POTASSIUM PUMP This is one of the most important
membrane pumps in animal cells The sodium-potassium pump is a
carrier protein that transports 3 sodium ions out of a cell and two potassium ions into the cellSodium is more concentrated outside the
cell and potassium is more concentrated inside
Both ions are actively transported The energy needed to power the pump
is supplied by ATP
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SODIUM-POTASSIUM PUMP
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VESICLES MOVE SUBSTANCES Proteins and polysaccharides are too
big to be moved by carrier proteins These substances are moved by
vesicles Movement into the cell by a vesicle is
endocytosis Movement out of the cell by a vesicle
is exocytosis http://bcs.whfreeman.com/thelife
wire8e/content/cat_040/0504003.html
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ENDOCYTOSIS
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EXOCYTOSIS
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HOW CELLS COMMUNICATE Cells need to be able to send and
receive signals to each other Cell release signal molecules that
carry info to other cellsHormones
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HOW CELLS COMMUNICATE
The cell membrane contains special proteins that bind to signal molecules to receive messages
Receptor proteins bind to a specific signal molecule allowing the
cell to respond to the signal
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RECEPTOR PROTEINS Most receptor proteins are embedded
in the lipid bilayer of cell membrane Binding a receptor protein to a signal
molecule changes the activity of the receiving cell
Changes 3 ways
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CHANGES IN PERMEABILITY Receptor proteins may bind with ion
channels Channels open when signal molecules
bind to the protein Important in
nervous system
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SECOND MESSENGERS Acts as a signal molecule in the
cytoplasm Amplifies the signal from the first
signal molecule
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ENZYME ACTION Receptor proteins may act as
enzymes They may speed up reactions when
the receptor protein and signal molecule bind
May also activate other enzymes