Transcript Homeostasis and Cell Transport

Chapter 5
HSCE: B2.5h
 Passive
 Active
transport (does not require energy)
transport (requires energy)
 Substances
can cross the cell membrane with
no energy required.
 Includes:

Diffusion



Facilitated (includes Ion Channels)
Simple
Osmosis
Concentration
Gradient-the
difference in the concentration of
molecules across a distance.
 Substances
naturally travel down their
concentration gradient (high to low
concentration).
 http://my.hrw.com/sh2/sh07_10/student/fla
sh/visual_concepts/60075.htm
Diffusion-Movement
of molecules
from an area of higher concentration
to an area of lower concentration
In the absence of other influences, diffusion will eventually cause
the molecules to be in EQUILIBRIUM


SIMPLE DIFFUSION- diffusion across a membrane
Cell membranes allow certain molecules to pass through,
but not others. Depends on the size and type of molecule.
Cell membrane
 Some
molecules are too large or are not
soluble in lipids (can’t pass the lipid bilayer).
They need the help of CARRIER PROTEINS.
 Does not require any extra energy to
transport the molecules because they are
still traveling from higher to lower
concentration (passive transport).
molecule
Cell membrane
(lipid bilayer)
carrier protein
 Facilitated
Diffusion
 Another
type of passive transport carries ions
across the membrane through proteins called
ION CHANNELS.
 Ions: sodium (Na+), potassium (K+), calcium
(Ca2+), chlorine (Cl-)
 Each type of ion channel is usually specific to
a certain ion.
 Some channels are always open, others have
“gates”.
IONS
Ion channel
 Osmosis-Movement
of WATER molecules
across a cell membrane from an area of
higher concentration to an area of low
concentration.
 Osmosis
 Passive
transport
 In a solution, a solute (the substance being
dissolved) is dissolved in a solvent (substance
doing the dissolving).
 Example:
SUGAR (solute) dissolves in WATER (solvent)
 In cells the solutes are organic molecules and
the solvent is water.
 OSMOSIS: the process by which water
molecules diffuse across a cell membrane
from an area of higher to lower
concentration.
Osmosis
solute
Water
molecules
Direction of
Water
movement
across the
membrane
Isotonic Solution
NO NET MOVEMENT OF
H2O (equal amounts
entering & leaving)
Hypotonic
Solution
Hypertonic
Solution
PLASMOLYSIS
CYTOLYSIS
Cell can burst
Cells shrink away
from cell wall, turgor
pressure lost
15
The pressure
exerted by water
inside the cell wall
is called
TURGOR PRESSURE
•When turgor
pressure is gained
and the cell bursts:
CYTOLYSIS
•When turgor
pressure is lost the
cell shrinks away
from the cell wall
and the plant wilts:
PLASMOLYSIS
External solution is
hypotonic to
cytosol: water
moves in…cell can
burst
Plasmolysis
External
solution is
isotonic to
cytosol: No net
movement
External solution
is hypertonic to
cytosol: water
moves out…cell
shrinks
Isotonic
Hypotonic
Hypertonic
17
10% NaCL
90% H2O
CELL
20% NaCL
80% H2O
What is the direction of water movement?
18
15% NaCL
85% H2O
ENVIRONMENT
CELL
5% NaCL
95% H2O
What is the direction of water movement?
19
10% NaCL
90% H2O
ENVIRONMENT
CELL
10% NaCL
90% H2O
NO NET
MOVEMENT
What is the direction of water movement?
equilibrium
The cell is at _______________.
20

Active transport moves substances against the
concentration gradient (from lower
concentration to higher).


Pumps


This requires energy most often supplied by ATP
Sodium-potassium pump
Movement in vesicles
Move macromolecules and nutrients that are too large
to pass the cell membrane or “packs” of small
molecules at the same time.
 Two types



Endocytosis
Exocytosis
Step 1-3: 3 Na+ bind to protein from inside the cell, a phosphate is removed
from ATP binding to the carrier protein and turning ATP into ADP. The protein
changes shape releasing the 3 Na+ to the outside.
Steps 4-6: The protein then picks up 2 K+ from the inside, the phosphate is
removed, changing the shape so that it releases the 2 K+ into the cell.
 sodium
potassium pump
Sodiumpotassium
pump
Pumps 3
Sodium ions
out of the cell
Pumps 2
Potassium ions
into the cell
This difference in charge is important
for the conduction of electrical
impulses along nerve cells.
Cells ingest (take in) external
fluid, macromolecules, and
large particles.
 External materials are
enclosed in a “pouch” that
pinches off from the cell and
becomes a membrane-bound
vesicle.
 Two main types

Pinocytosis- transports fluids or
solutes
 Phagocytosis- transports large
particles or whole cells.

Endocytosis – Phagocytosis
Used to engulf large particles such as
food, bacteria, etc. into vesicles
Called “Cell Eating”
26
 Many
unicellular organisms feed by the
process of phagocytosis.
 Certain cells (Phagocytes) in animals use
phagocytosis to ingest bacteria and viruses
that invade the body.
Pinocytosis
Most common form of endocytosis.
Takes in dissolved molecules as a vesicle.
28
 Process
by which a substrate is released from
the cell through a vesicle.
Homeostasis
Is aided by
Passive transport
Cell transport
which includes
Active transport
Such as
Such as
Of substance
down their
Concentration
gradient
Of substances
against their
Osmosis
Endocytosis
Diffusion
Exocytosis
Facilitated
diffusion
Which use a
Carrier Protein
Sodium-potassium
pump
Three Forms of Transport Across the Membrane
Active transport
31