Download Homeostasis & Transport

Homeostasis &
Transport
Homeostasis
Passive Transport
 Active Transport
Homeostasis
Plasma Membrane
Structure
Membrane Protein
Functions
Passive Transport
• Diffusion
 Equilibrium
 Diffusion across membranes
• Osmosis:
 Direction of osmosis
 How cells deal with osmosis
• Facilitated Diffusion
• Ion Channels
Learning
Objectives
1. Explain how an equilibrium is
established as a result of diffusion
2. Distinguish btw/ diffusion & osmosis
3. Explain how substances cross the
cell membrane through facilitated
diffusion
4. Explain how ion channels assist the
diffusion of ions across the cell
membrane
Diffusion
• Diffusion
 The movement of molecules from
an area of higher concentration to
an area of lower concentration
until equilibrium is reached
• Concentration Gradient
 The difference in concentration of
molecules across space
 Molecules diffuse down their
concentration gradients
Diffusion
• The movement of substances from
a region of high concentration to a
region of low concentration until
equilibrium is reached
Simple Diffusion
• To View Video:
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– When hand appears, click once
• MOV Video plays about 30 sec
Equilibrium
• Equilibrium
 The equal concentration of
molecules throughout the space
they occupy
 Random movement of molecules
continues at equilibrium but there
is no concentration gradient
 Molecules are just as likely to
move in one direction as in any
other
Diffusion Across
A Membrane
Diffusion
Osmosis
• Osmosis
 The process by which water
molecules diffuse across a cell
membrane from an area of higher
concentration to an area of lower
concentration
• Direction of Osmosis
 Depends on the relative
concentration of solutes on the
two sides of the cell membrane
Direction of Osmosis
• If [solute] in cytosol > [solute]
outside cell
 water diffuses INTO the cell
 A solution w/ higher [solute] is said
to be hypertonic
• If [solute] outside cell > [solute]
in cytosol
 water diffuses OUT OF the cell
 A solution w/ lower [solute] is said
to be hypotonic
Direction of Osmosis
• If [solute] in cytosol = [solute]
outside cell
 water diffuses equally in both
directions
 there is no net gain or loss of
water by the cell
 Solutions w/ equal [solute] are said
to be isotonic
Osmosis
• To View Video:
– Move mouse cursor over slide titlelink
– When hand appears, click once
• MOV Video plays about 30 sec
Tonicity &
Water Concentration
• Hypotonic Solution:
 ↓ [solute]
↑ [H2O]
• Hypertonic Solution:
 ↑ [solute]
↓ [H2O]
• Isotonic Solutions:
 solute concentrations equal
 water concentrations equal
How Cells
Deal With Osmosis
• Cells in isotonic conditions have no
trouble maintaining water balance
(homeostasis)
 Land vertebrates
 Most marine organisms
• Many cells function in hypotonic
environments
 Unicellular freshwater organisms
Osmoregulation
Contractile
vacuole - full
RBCs & Tonicity
Plant Cells & Tonicity
Facilitated Diffusion
• Facilitated Diffusion
 The process by which a substance
moves down its concentration
gradient across a cell membrane
with the assistance of a carrier
protein
• Carrier Protein
 A membrane protein that
transports specific substances
across a cell membrane
Facilitated
Diffusion
• Substances
using facilitated
diffusion:
– Large, water
soluble
molecules
– Charged (+ or -)
molecules or
ions
Facilitated Diffusion
Facilitated Diffusion
• To View Video:
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– When hand appears, click once
• MOV Video plays about 30 sec
Diffusion Through
Ion Channels
• Ion channel
 A membrane protein that provides
a passageway across a cell
membrane through which an ion
can diffuse
• Channel Types
 Open channels – always remain
open
 Gated channels – can open or close
in response to a stimulus
Ion Channels
ION CHANNELS
Channel Protein
Function
• To View Video:
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• MOV Video plays about 30 sec
Passive Transport &
Membrane Permeability
Passive -v- Active
Transport
• Passive Transport:
 Occurs w/out energy input from
ATP
 Ex: simple diffusion; osmosis;
facilitated diffusion; ion channels
• Active Transport:
 Requires energy input from ATP
 Ex: ion pumps; vesicular transport
Active Transport
• Cell Membrane Pumps
 Sodium-potassium Pump
• Vesicular Transport:
 Endocytosis
 Exocytosis
Learning
Objectives
1. Distinguish btw/ passive
transport & active transport
2. Explain how the sodiumpotassium pump operates
3. Compare & contrast
endocytosis & exocytosis
Cell Membrane Pumps
• Sodium-potassium Pump
 Carrier protein that actively transports
Na ions out of & K ions into the cell
 Pumps Na+ & K+ against their
concentration gradients
 Requires energy from ATP
• Proton Pump
 Carrier protein that actively transports
H+ ions against their concentration
gradient
 Important in photosynthesis & cellular
respiration
Protein Pump Function
• To View Video:
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– When hand appears, click once
• MOV Video plays about 30 sec
+
Na
-
+
K
Exchange Pump
Na-K Ion Pump
• To View Video:
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– When hand appears, click once
• MOV Video plays about 1 min
Proton Pump
Endocytosis &
Exocytosis
• To View Video:
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– When hand appears, click once
• MOV Video plays about 30 sec
Vesicular Transport
• Endocytosis
 Process by which a cell surrounds
& engulfs substances
 Requires energy from ATP to form
vesicle
• Types of Endocytosis:
 Pinocytosis – cell engulfs fluids
&/or solutes
 Phagocytosis – cell engulfs large
particles or whole cells
Phagocytosis
Paramecium in
of Paramecium
food vacuoleby Amoeba
lysosomes
Amoeba is a
phagocyte
Vesicular Transport
• Exocytosis
 Process by which a vesicle inside a
cell fuses w/ the cell membrane &
releases its contents to the
external environment
 Requires energy from ATP to move
vesicle to cell membrane
Vesicular Transport
• To View Video:
– Move mouse cursor over slide titlelink
– When hand appears, click once
• MOV Video plays about 30 sec
Endocytosis &
Exocytosis in a WBC