Transcript Chapter 5: Homeostasis and Transport

Chapter 5:
Homeostasis and
Transport
Section 5-1:
Passive Transport
• Cell membrane helps organisms maintain
homeostasis by controlling what
enters/exits cell
• Some substance can cross cell membrane
with out using energy from cell
• PASSIVE TRANSPORT
Diffusion
• Simplest
• movement of
substances
from area of
high
concentration
to area of low
concentration
• Driven by kinetic energy that molecules
posses
• kinetic energy = molecules constantly in
motion
• Move randomly in straight line until they hit
an object  Move in straight line in
concentration gradient because to
molecule to bounce off of
Concentration Gradient
• Difference in concentration of molecules
across a space
Equilibrium
• When the concentration of molecules of a
substance is the same throughout a space
• Even at equilibrium the random motions of
molecules still occur
• Random motions on one direction balance
out those of the other direction
Diffusion Across Membrane
• If molecules can diffusion across cell
membrane it will move from high
concentration to low concentration
• Ability of molecule to move across
membrane depends on:
– size
– type of molecule
– chemical nature of membrane
• Membrane = phospholipids
• THUS any substance that can dissolve in
lipids will pass through membrane
• Also VERY small molecule can fit through
pores even if they are not soluble in lipids
REMEMBER
• Chapter 2:
Solution = solute dissolved in solvent
• CELLS:
Solutes = organic and inorganic molecules
Solvents= water
Osmosis
• Process by which water molecules diffuse
across cell membrane from high
concentration to low concentration
• Does not cost cell energy to occur
Direction of Osmosis
• Net direction of osmosis depends on
relative concentration of solutes on
either side of membrane
Name
Solutes
Movement
concentration of water
Hypotonic
More solute in
cytosol; lower
concentration
outside cell
Less solute in
cytosol; higher
concentration
outside cell
Same
concentration
in/out
Hypertonic
Isotonic
Effect on
cell
Water
Cell
moves INTO enlarges
cell
Water
Cell
moves OUT shrinks
of cell
Water
Cell
moves in/out remains
at equal
same size
rates
Put it together...
• If a solution is hypotonic then the cytosol is
hypertonic
• If solution is hypertonic then cytosol is
hypotonic
Cell Environments
• Isotonic environment  cells are fine
(cells of vertebrate animals on land or sea
animals)
• Cells in hypotonic environment  cells
must rid themselves of excess water
(unicellular organisms in FRESH water)
How do cells deal with osmosis?
1- Contractile vacuoles
2- Solute Pumps
3- Cell Walls
• How some unicellular
organisms rid
themselves of
excess water
• Organelle which
removes water
• How?
Collect excess
water and then
contract,
pumping
water out of cell
**REQUIRES ENERGY**
Contractile
Vacuoles
Solute Pumps
• Mostly in multicellular
organisms
• Pump solutes OUT of
cytosol
• Bring cytosol solute
concentration closer
to that of the solution
• water less likely to
move into cell
Cell Walls
• Plant roots swell as they absorb water
• Swelling stops when cell membrane is
pressed against cell wall
• Cells walls able to
withstand
pressure of water
• Turgor pressure:
pressure that
water molecules
exert against cell
wall
Plasmolysis
• In hypertonic
environment
water leaves cells
• Cells shrink away
from cells walls
• Turgor pressure is
lost
• Plants wilt
Cytolysis
• Bursting of cells
• Cells which lack contractile vacuoles,
solute pumps, and cells walls
• Water continuously moves into cells
Facilitated Diffusion
• Process used for
molecules that
cannot diffuse
rapidly through cell
membranes
• Why not?
– Not soluble in lipids
– Too large to pass
through pores
Carrier Proteins
• Assist in diffusion of insoluble/large
molecules across membrane
• STILL PASSIVE!
• Molecules moved
from high
concentration
to low
concentration
How carrier proteins work…
1. Carrier proteins binds to molecules it
transports
2. Carrier protein changes shape
3. Protein shields molecules from
hydrophobic area of membrane
4. Molecule transported through membrane
5. Molecule released into/out of cell
6. Protein returns to original shape
Transport of Glucose
• Facilitated
diffusion
• Glucose
molecules too
large
• Cells need for
energy
• Carrier proteins
are specific for
certain molecules
Diffusion through Ion Channels
• Passive transport involving membrane
proteins
• Ions: Na+, K+, Ca2+, and Cl• Each type of ion has specific ion channel
• Some ion channels always
open
• Others have “gates”
that open to allows
OR close
• Gates may open due
to three kinds of
stimuli
– Stretching of cell membrane
– Electrical signals
– Chemicals in cytosol or
external environment
5-2: Active Transport
• Sometimes cells
must move
materials against
concentration
gradient
[low]  [high]
• Active transport:
requires cell to use
energy
Cell Membrane Pumps
• Some carrier proteins also help active
transport
• Same “Bind-Change shape-TransportReturn shape” process
Sodium-Potassium Pump
• Transport Na + and K +
• Most animals cells must have high Na +
outside of cells and low K + inside cell
Process
1. Three Na + ions bind to sodiumpotassium pump WHILE carrier protein
split phosphate group from ATP
molecule
2. Phosphate group
binds to carrier
protein and
changes carrier
protein shape
3. Now has shape need to bind two K + ions
4. When K + ions bind, phosphate group
releases and carrier protein changes
shape again
5. K + ions
released
into cell
6. Ready to
do it again!
Summary of Sodium-potassium
Transport…
• 3 Na + ions now outside
• 2 K + ions now inside
• Usually about 450 Na + ions
and 300 K +
PER SECOND!
• Movement of 3:2 Na + :K + ions create
electrical gradient
• Outside :positively charged
• Inside :negatively charged
• IMPORTANCE: conduction of electrical
impulses along nerve cells
For things too large…
• Macromolecules
• Food particles
• Types:
– Endocytosis
(endo in/enter)
– Exocytosis
(exo out/exit)
Endocytosis
• Cells ingest external fluid,
macromolecules, and large particles
(including other cells)
• Pouch formed  Materials enclosed by
portion of cell
• Vesicle: membrane
bound organelle
consisting of pinched
off pouch from cell
membrane
• Some vesicles fuse
with lysosomes to
digest materials
Type of Endocytosis
Based on kind of material taken in:
• Pinocytosis
• Phagocytosis
Pinocytosis
• transport of solutes or fluids
Phagocytosis
• movement of large
particles or whole cells
– how some organisms
feed
– how animal cells ingest
bacteria and viruses
• Phagocytes: cells that
allow lysosomes to fuse
with vesicles that
contain harmful things
Exocytosis
• Reverse of endocytosis
• Vesicle fuse with cell membrane and
release content’s into cell environment
• Cell may use to release proteins