Download Ch. 8: Transport Across the Cell Membrane

NOTES: 7.3-7.4
CELL TRANSPORT &
HOMEOSTASIS
Selectively permeable:
● property of biological membranes which
allows some substances to pass more easily
than others
Transport proteins:
● membrane proteins that transport
SPECIFIC molecules or ions across
biological membranes
GLUCOSE
Binding
Recovery
Transport
Dissociation
Movement across the cell membrane can be:
1) PASSIVE


cell does not have to spend
energy
substance moves from where it
is MORE concentrated to where
it is LESS concentrated.
2) ACTIVE
 cell “spends” energy to move a
substance from where it is LESS
concentrated to where it is
MORE concentrated (“UPHILL”)
Passive Transport:
DIFFUSION
● movement of a substance
from where it is conc. to
where it is less conc. (“down
a concentration gradient”)
Passive Transport:
FACILITATED DIFFUSION
● diffusion of solutes across a membrane, with
the help of transport proteins
(passive transport because it is movement
down a concentration gradient; cell does not
need to spend any energy)
Passive Transport / Fac. Diffusion:
OSMOSIS
● diffusion of WATER
through a selectively
permeable membrane;
water moves DOWN its
concentration gradient
(which is to say opposite
the solute concentration!)
● OSMOSIS:(this is a type of facilitated
diffusion…water moves through special
channels in cell membrane called
aquaporins)
OUTSIDE
THE CELL
INSIDE
THE CELL
– the direction of water movement can be
described / predicted based on if the cell’s
ENVIRONMENT is:
● ISOTONIC: equal solute concentration
compared to inside a cell
● HYPERTONIC: greater solute
concentration than inside a cell
● HYPOTONIC: lower solute concentration
compared to inside a cell
WATER MOVES FROM HYPO
TO HYPERTONIC!!!
In animal cells:
● in a HYPERTONIC environment,
water exits the cell;
cells shrivel and usually die
● in a HYPOTONIC environment,
water moves into cell,
causing it to swell and
possibly burst
In cells with cell walls (i.e. plant cells):
● in a HYPERTONIC environment, water exits
the cell; cells shrivel and usually die
● in a HYPOTONIC environment, water moves
into cell, causing it to swell; cells become
more TURGID.
ACTIVE TRANSPORT: energy-requiring
process; molecules are moved across the
cell membrane AGAINST their
concentration gradient (“uphill”)
Active Transport:
● Molecular Transport
● Bulk Transport
Active Transport:
● Molecular Transport
-small molecules &
ions are moved
across membranes
by proteins that
act like pumps
BULK TRANSPORT:
ENDOCYTOSIS & EXOCYTOSIS
● transport of large molecules (e.g. proteins and
polysaccharides) into or out of the cell
ENDOCYTOSIS
*importing large
molecules by forming
vesicles out of the cell
membrane
**vesicle forms in a small
region of cell membrane
***used by cells to bring in
larger, extracellular
substances (e.g. proteins)
EXOCYTOSIS
ENDOCYTOSIS
EXOCYTOSIS
*exporting large
molecules by vesicles
fusing w / the cell
membrane
**vesicle buds from ER
or Golgi and migrates to
cell membrane
***used by cells to
export products (e.g.
cells in pancreas
secreting insulin)
2 types of Endocytosis:
1) Phagocytosis: solid particles (“cell
eating”)
2) Pinocytosis: fluid droplets (“cell
drinking”)
Phagocytosis
Pinocytosis
7.4: Homeostasis & Cells
● sometimes an organism can be a single
cell
● unicellular organisms dominate life on
Earth…they include:
-prokaryotes: bacteria
-eukaryotes: protists (amoeba,
paramecium, Euglena)
-eukaryotes: unicellular fungi (yeast)
Unicellular Organisms:
● unicellular organisms must maintain
homeostasis
● HOMEOSTASIS: relatively constant
internal physical & chemical conditions
● to maintain homeostasis, unicellular
organisms grow, respond to the
environment, transform energy, and
reproduce
Multicellular Life
● the cells in a
multicellular organism
must work together to
maintain homeostasis
● in a multicellular
organism, cells become
specialized so that
different cell types play
different roles
CELL SPECIALIZATION:
● some cells are specialized to MOVE
(i.e. muscle cells)
● some cells are specialized to RESPOND
(i.e. nerve cells)
CELL SPECIALIZATION:
● some cells are
specialized to
transport
substances (i.e. red
blood cells)
● some cells are
specialized to fight
off pathogens (i.e.
white blood cells)
LEVELS OF ORGANIZATION:
● CELLS…are
organized into…
● TISSUES: group
of similar cells
performing the
same function
LEVELS OF ORGANIZATION:
● ORGAN: group of
tissues working
together
-ex: stomach
● ORGAN SYSTEM:
group of organs
working together
-ex: digestive system
(stomach, intestines,
pancreas, etc.)
LEVELS OF ORGANIZATION:
● ORGANISM: collection of all of the
above!...specialization and
interdependence at all levels allows an
organism to maintain homeostasis!
CELLULAR COMMUNICATION:
● Cells communicate with one another by
using chemical signals (i.e. hormones)
● in order to respond to a particular
chemical signal, a cell must have the
appropriate RECEPTOR to which the
signaling molecule can bind
CELLULAR COMMUNICATION:
● cells respond to chemical
signals in a variety of
ways:
-muscle cell contracts
-liver cell takes up & stores
glucose from blood
-skin cells divide to replace
injured cells