Transcript Chapter 5

Chapter 5
“Homeostasis
and Cell
Transport”
Section 1: “Passive Transport”
What part of a cell maintains
homeostasis?
Cell Membrane is selectively permeable
Passive transport
– movement of molecules across a cell
membrane without energy expenditure.
Types of Passive transport:
1. Diffusion
2. Osmosis
3. Facilitated Diffusion
4. Ion Channels
1.
Diffusion
– movement of molecules from an area of [high] to
an area of [low].
High
Low
The steeper the slope, the
faster the rate of diffusion.
Therefore, the greater the
concentration differential,
the faster the rate of
diffusion.
Concentration gradient – difference in concentration
between two areas
- No energy is required to go from high to low [ ].
Totally driven by molecules’ kinetic energy –
constant motion.
• Movement of molecules continue until they
reach equilibrium.
• An increase in temperature increases the kinetic
energy of the molecules, therefore diffusion
occurs faster.
– Why sugar “melts” faster in hot vs. cold water
• Diffusion occurs across the cell membrane
• Dependent upon:
– size of molecules
– size of membrane pores
– chemistry of molecules (CO2 and O2) –
nonpolar and noncharged except WATER
2. Osmosis = diffusion of water across a
membrane
- net movement of water from [high] ---> [low]
- direction of water movement depends on the
[ ] of solutes onInside
two sides (inside the cell
and
Outside
outside the cell)
HYPERTONIC
VS.
HYPOTONIC
Red Blood Cells in isotonic,
hypotonic and hypertonic
solutions (left to right)
Isotonic
Hypotonic
Cytolysis
Hypertonic
Crenation
Hypertonic
• Hypertonic Solution:
[Solute] outside the cell is higher than inside the
cytosol
– More dissolved particles outside of cell than
inside of cell; more water inside
• Hyper = more of something
• Tonic = dissolved particles/solutes
– Water moves out of the cell into solution
– Cell shrinks
– What happens when you put salt on a slug?
– Salting meat
Elodea
Plasmolysis
loss of turgor pressure and cytoplasmic
structure due to water in a plant cell
Hypotonic
Hypotonic Solution:
[Solute] outside is lower than inside cell
– Less dissolved particles outside of cell than
inside of cell; less water inside
• Hypo = less, under
• Tonic = dissolved particles/solute
– Water moves into cell from solution
– Cell expands (and may burst)
• Isotonic Solution:
– Solute
concentration of
solution equal to
that of cell
• No net water
movement
• Most cells exists
in an isotonic
external
environment
Quick Review…
Turgor Pressure
Plasmyolysis
Real Concentration Problems
1) Paramecium live in freshwater. They
have a 3% salt internal environment.
How do they keep from exploding in this
hypotonic environment?
2) Other organisms live in a salt water
environment. How do they keep their
cells from shriveling up?
3) What do plants do?
4) How do your kidneys work?
Freshwater Problem
http://www.youtube.com/watch?v=pahUt0R
CKYc
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Plants
Plants usually exist in a hypotonic
environment.
Cells don’t burst due to flexible and strong
cell wall.
Saltwater critters
They pump out excess salt, or pump in
water.
Your kidneys
Extremely important organs in maintaining
osmotic balance (isotonicity) with body
fluids.
3. Facilitated diffusion
- Diffusion with assistance from carrier
proteins.
-can’t occur fast enough, chemistry is
different, or too large to pass through
pores.
- transport may occur into or out of cell.
- carrier proteins are specific to one 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 and
goes back to its original shape.
Occurs with glucose (that can’t pass
through cell on its own).
4. Diffusion thru Ion Channels
– Na+, K+, Ca2+, and Cl- cannot pass through
the
membrane.
- Recall that ions cannot pass since they
aren’t soluble in lipids.
- Therefore, they need ion channels to
provide a small passageway for them.
- Conditions for ion channel gates to open.
1. Stretching of cell membrane
2. Electrical signals
3. Chemicals in cytoplasm
or external environment
Section 5.2 “Active Transport”
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Movement of molecules from [Low] to [High]
Movement is against the gradient
Energy is needed
Cell Membrane “Pumps”
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http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_the_so
dium_potassium_pump_works.html
– Sodium – Potassium pump –
– Transports Na+ and K+ up [ ] gradient
– Important for transmission of signals between
nerve cells
Exocytosis and Endocytosis
* Engulfing/releasing of macromolecules
and food particles/wastes into/out of the
cell membrane
* Uses the cell membrane to make vesicles
Animation 1
Animation 2
Endocytosis
– Cells ingest external fluids,
macromolecules and 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
Two Types of Endocytosis:
– Pinocytosis (cell drinking) if solutes or
fluids are involved
– Phagocytosis (cell eating) if large particles or
whole cells are involved Occurs with bacteria,
viruses or phagocytes (WBC)
Exocytosis
– Release of vesicles through 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