Download Cell TRANSPORT standard: eq: how does the cell membrane help

CELL TRANSPORT
SB1D. EXPLAIN HOMEOSTASIS AND DESCRIBE
THE MOVEMENT OF MATERIALS THROUGH
THE CELL MEMBRANE. EXPLAIN THE IMPACT
OF WATER ON LIFE PROCESSES
EQ: HOW DOES THE CELL MEMBRANE HELP
THE CELL MAINTAIN HOMEOSTASIS?
Cell Transport
The cell must move different substances into and out
of the cell
This happens in a variety of ways…
Sometimes the cell has to use energy, sometimes they do not
Passive Transport
Diffusion - passive transport of substances DOWN a
concentration gradient (from high to low
concentration)
Concentration gradient - one area has a higher
concentration than another area
Equilibrium - when a space is filled evenly
Diffusion is simplest type of passive transport
Some substance diffuse through lipid bilayer
Others though transport proteins
Diffusion
Cell membrane is selectively permeable
Nonpolar interior of lipid bilayer repels ions and most
polar molecules
These substances are prevented from diffusing across
membrane
Very small or nonpolar molecules can diffuse across the
membrane down their concentration gradient
Simple Diffusion
Moves small, nonpolar molecules directly through
lipid bilayer
ExO2
CO2
Facilitated Diffusion
o Moves ions and polar molecules that simple diffusion
cannot
o Transport proteins help these substances diffuse
through the cell membrane
o Two types:
 Channel protein
Carrier protein
Channel Proteins
Ions, sugars, and amino acids can diffuse with help of
channel proteins
Proteins, sometimes called pores, serve as tunnels
through the lipid bilayer
Each channel allows the diffusion of a specific substance
Ex - only sodium ions can pass through sodium ion channels
Carrier
Protein
Transport substances that fit within their binding site
(1)Carrier protein binds to specific substances on one
side of cell membrane
(2)Binding causes protein to change shape
(3)As shape changes, the substance is moved across the
cell membrane and released on other side
Facilitated Diffusion
Diffusion
Model of Diffusion
Osmosis
Definition - diffusion of water across selectively
permeable membrane
Type of diffusion (passive transport)
From high to low concentration
Allows cells to maintain water balance as environment
changes
Pass through water channels
Protein channels specific to water..
Osmosis
There are three possibilities for the direction of
water movement:
Water moves out - (hypertonic solution)
Causes cell to shrink
Water moves in - (hypotonic solution)
Causes cell to swell
Cell could burst if it swells too much
Plant cells have rigid cell wall to prevent this
No net water movement - (isotonic solution)
No change in cell volume
Osmosis
Hypertonic, Hypotonic, and Isotonic
Solutions
Active Transport
Transports substances against concentration
gradient
Low to high concentration
Active Transport - requires energy
Most energy supplied directly or indirectly in the form
of ATP (adenosine triphosphate)
Pumps
Substances bind to carrier proteins in low
concentrations, released in higher concentration
Carrier proteins function as “pumps” - move
substances against their concentration gradient called
membrane pumps
Movement in Vesicles
Many substances, like proteins and polysaccharides,
are too large to be transported by carrier proteins
So, they are moved across the cell membrane by vesicles
The movement of a substance into a cell by a vesicle is
called endocytosis
Pinocytosis- “cell drinking”
Phagocytosis- “cell eating”
The movement of a substance by a vesicle to the
outside of a cell is called exocytosis
ENDOCYTOSIS
EXOCYTOSIS