Transcript Chapter 5

Chapter 5
Homeostasis
and Transport
What part of a cell maintains it homeostasis?
Cell Membrane is selectively permeable
Regulates what goes in and out of a cell
Passive transport
– movement of molecule across a cell
membrane w/o energy expenditure.
Types of Passive transport
– Diffusion
– Osmosis
– Facilitated Diffusion
– Ion Channels
1.
Diffusion
– movement of molecules from an area of [High] to
an area of [low].
The steeper the slope, the
faster the rate of diffusion.
High
Low
Therefore, the greater the
concentration differential,
the faster the rate of
diffusion
Concentration gradient
- No energy is required to go from High to low [ ].
Totally driven by molecules’ kinetic energy –
constant motion.
Demos with Air freshener, Potassium Permangenate
• Movement of molecules continues until they
reach Equilibrium
• An increase in temperature, > the kinetic
energy of the molecules therefore diffusion
occurs faster.
– Why sugar “melts” faster in hot water over cold
• May occur across the cell membrane
• Dependant on:
– size of molecules
– size of pores
– & solubility of molecules (CO2 & O2) easily go into
solution into bilipid layer.
Demo with Ammonia and phenolphthalein
2. Osmosis - [ ] means concentration
- net movement of water from [high] ---> [low]
through a membrane
Direction of water movement depends on the
[ ] of solutes on 2 sides (inside the cell and
outside the cell
Water Molecules move from where there is a lower solute concentration
to a higher solute concentration
Demonstration of osmosis
What is happening to:
the water (blue)
and the dissolved substances
(green and red).
What is the same?
What is different?
Hypertonic
• Hypertonic Solution:
[Solute] outside the cell is higher than inside
the cytosol
– More dissolved particles outside of cell than
inside of cell
• Hyper = more;
• Tonic = dissolved particles/solutes
– Water moves out of cell into solution
– Cell shrinks
– What happens when you put salt on a slug?
Red Blood Cells in a normal
solute concentation, freshwater
and then salt
Elodea
Plasmolysis*
- loss of cytoplasmic structure due to
water.
Hypotonic
Hypotonic Solution:
[Solute] concentration outside is lower
than cytosol
– Less dissolved particles outside of cell
than inside of cell
• Hypo = less, under
• Tonic = dissolved particles/solute
– Water moves into cell from solution
– Cell expands(and may burst)
Hypotonic
• Turgidity - swollen cells due to water
gain. Plant cells depend on this!
• Cytolysis (bursting) may result.
• Isotonic Solution:
– Solute
concentration of
solution equal to that
of cell
• No net water
movement
• Most cells exists
in an isotonic
external
environment
Turgor Pressure
Plasmyolysis
• Plants usually exist in a hypotonic
environment.
• Cells don’t burst due to flexible &
strong cell wall.
• Turgor pressure – pressure exerted by
water on a plant’s cell wall.
Part 2 of Diffusion/Osmosis lab
GlucoseStarch
Iodine
Solution
Iodine Solution
Glucose-Starch
Solution
Iodine Solution
A
Glucose-Starch
Solution
B
Osmosis Grape Lab
Day 1
Mass
(grams)
Day 2
Mass
(grams)
Difference
in Mass
(grams)
Net
Movement of
water
Percent
(Into grape,
Change out of grape
or no net
movement)
Type of
Solution
(Hypotonic,
Isotonic,
Hypertonic)
Distilled
water
Grape
Juice
Salt
Water
Percent Change = Day 2 – Day 1 Mass x 100
Day 1 Mass
Quiz
Paramecium live in freshwater. They
have a 3% salt internal environment.
How do they keep from exploding in
this hypotonic environment?
Contractile Vacuoles
– Organelles found in unicellular
organisms that collect, then pump out
excess water that enters through
osmosis.
Does require energy.
Like a sump pump in your basement!
Contractile Vacuoles
Facilitated diffusion
Diffusion with assistance from
Carrier proteins.
Can’t occur fast enough on their own or
too large to pass through pores.
May occur into or out of cell.
Carrier proteins are specific to 1 type of
molecule.
Animation
Steps in Facilitated Diffusion:
1. Carrier protein binds to molecule to
be transported.
2. Carrier protein changes shape
(shielding it from hydrophobic
interior of bilipid layer).
3. Carrier protein releases molecule &
goes back to its original shape.
Occurs with glucose & amino acids
(that can’t pass through cell on their
own).
Diffusion thru Ion Channels
– Na+, K+, Ca2+, & Cl- cannot pass thru the
membrane.
Ions can not pass since ions aren’t soluble
in lipids.
Therefore, they need ion channels to
provide a small passageway for each ion.
Conditions for ion channel gates to open.
1. Stretching of cell membrane
2. Electrical signals
3. Chemicals in cytosol
or external environment.
Active Transport
• Movement of molecules from [Low] to [High].
Energy is needed
• Cell Membrane Pumps
– Use Carrier Proteins and becomes cell membrane
pumps
• Sodium – Potassium pump - Transports Na+
and K+ up [ ] gradient
– 3 Na+ from cytosol bind to the carrier protein
– Carrier proteins breaks ATP to ADP + P, P group binds to
Carrier protein
– 3 Na+ are released to environment. Carrier protein changes
shape.
– 2 K+ from outside cell bind to Carrier protein
– With release of P group, K+ ions released into cytosol
– Cycle repeats
– Top speed – 450 Na+ & 300 K+ per second
– Inside of cell membrane is now negatively charged,
outside is positive. Difference is necessary for electrical
impulses along nerve cells.
– McGraw Hill video
Endocytosis and Exocytosis
Engulfing of macromolecules & food
particles into the cell membrane
Animation 1
Animation 2
Endocytosis
– Cells ingest external fluids,
macromolecules & large particles.
• Cell membrane surrounds material into a
pouch.
• Cell membrane around pouch pinches together
to form a vesicle.
• Vesicle may fuse with lysosome for digestion
2 Types of Endocytosis
– Pinocytosis (cell drinking) if solutes or
fluids are involved
– Phagocytosis (cell eating) if large particles
or whole cells are involved
Another animation
Occurs with bacteria, viruses or
phagocytes (WBC)
Exocytosis
– Release of vesicles thru cell
membrane. May be proteins, waste
materials, or indigestibles.
• Vesicles fuse with membrane, release contents
into environment
• Proteins packaged by Golgi Apparatus into
vesicles which fuse with membrane to release
excess proteins
• Animation
Vocabulary
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Carrier protein
Hypotonic
Concentration gradient
Ion channel
Contractile vacuole
Isotonic
Cytolysis
Osmosis
Phagocytosis
Vesicle
Endocytosis
Pinocytosis
Diffusion
Passive transport
Equilibrium
Plasmolysis
Facilitated Diffusion
Turgor pressure
Hypertonic
Active transport
Sodium – K pump
Exocytosis
Phagocytosis