Transcript HOMEOSTASIS and TRANSPORT

HOMEOSTASIS and TRANSPORT
A4
A4. Homeostasis and Transport
1. Describe how the structure of the plasma membrane
allows it to function as a regulatory structure and/or
protective barrier for a cell.
2. Compare the mechanisms that transport materials
across the plasma membrane.
3. Explain how organisms maintain homeostasis.
4. Describe how membrane-bound organelles facilitate
the transport of materials within a cell.
A4. Vocabulary
plasma membrane
phospholipid
selectively permeable
protein pump
diffusion
active transport
endocytosis
isotonic
hypertonic
hypotonic
lipid bilayer
impermeable
protein channel
osmosis
facilitated diffusion
passive transport
exocytosis
equilibrium
concentration gradient
homeostasis
Cell Membrane Structure and function
• Aka cell membrane
• Surrounds the cytoplasm of the cell, controlling
what enters and exits
• Selectively permeable = some substances cross
more easily than others
Cell Membrane Structure and function
• Membranes are made of 2 layers of phospholipids
• Each phospholipid has a “head” and two “tails”
– The head loves water (polar; hydrophilic)
– The tails hate water (nonpolar; hydrophobic)
• Nonpolar hydrophobic center determines how
easily substances move across the membrane
Cell Membrane Structure and Function
DRAW THIS
in your
NOTES!!
Cell Membrane Structure and Function
Membranes are selectively permeable
• Some things cross the membrane (permeable)
– Small, nonpolar molecules such as oxygen and carbon dioxide
• Ions and polar molecules are repelled by the
hydrophobic center and therefore need the help of
proteins in the membrane
– Ions, polar molecules, proteins, larger particles
• Some things can’t cross the membrane (impermeable)
Cell Membrane Structure and Function
• Stabilize and shape the membrane
• Hormones bind to receptors for cell communication
• Transport proteins aid in movement of material
– Aquaporins = protein channels allow easy passage of water
– Protein channels/carriers
– Protein pumps
Let’s Build a Model of a cell membrane!
• Cotton swabs represent phospholipids
• Other components are embedded within the
phospholipid bilayer
• Can you move the components back and
forth?
Cell Membrane Structure and Function
• The cell membrane acts as a fluid…
– It is not rigid
– Proteins and phospholipids can move around
• The cell membrane is a mosaic…
– Many different parts make up the cell membrane
Cell Membrane Structure and Function
• Many organelles are surrounded by membranes
– EX: Chloroplast, golgi, mitochondria, ER, nucleus, etc.
• Endosymbiosis
– Theory that suggests that cell organelles were once free
living organisms that were captured by a eukaryotic cell
Can you do it?
• Give as many names for the boundary of the
cell as you can…
Mechanisms of Passive Transport
• requires NO energy
• Depends on a concentration gradient
– Concentration = relative amount of substance
– gradient = difference
• SUBSTANCE moves from HIGH concentration to
LOW concentration
• Some materials can pass freely, other materials need
a protein channel
• Examples: diffusion, osmosis, facilitated diffusion
Mechanisms of Passive Transport
Mechanisms of Passive Transport
• Passive transport of small nonpolar molecules
through the phospholipid bilayer
• Equilibrium is reached when there is no more
concentration gradient
Mechanisms of Passive Transport
Concentration gradient
HIGH  LOW
EQUILIBRIUM
Mechanisms of Passive Transport
Mechanisms of Passive Transport
• Passive transport of ions and polar molecules
• Relies on protein channels or carrier proteins to
help material cross the membrane
• EX: glucose transport
Mechanisms of Passive Transport
Mechanisms of Passive Transport
Cell Membrane Structure and Function
Which of the following is NOT an example
of passive transport?
A.
B.
C.
D.
Carbon dioxide crossing vessels in the lung
Oxygen dissolved in the blood crosses the membrane
of a red blood cell
Glucose molecules are transported by a protein carrier
Sodium ions move through a protein channel until
there is a higher concentration of sodium in the cell
Mechanisms of Passive Transport
• Diffusion of water
• WATER moves in the direction of higher solute
concentration
• Water movement causes a change in the volume of a
cell
• Osmosis plays a role in maintaining homeostasis (osmosregulation)
• Aquaporins = protein channels for water to pass
Mechanisms of Passive Transport
solute
water
Mechanisms of Passive Transport
• Fluids inside and outside of a cell can be compared
in terms of solute concentration
– Isotonic = solute concentration is equal
– Hypotonic = solute concentration is low
– Hypertonic = solute concentration is high
Mechanisms of Passive Transport
• Amount of water inside =
amount of water outside
• Water moves back and forth
across the membrane equally
in both directions
• Equilibrium = equal
concentrations of water on
both sides of the membrane
Mechanisms of Passive Transport
• Solution contains LOW
solute
• EX: pure water
• Water moves INTO the cell
• Cell swells
– plant cells are protected by
the cell wall
– animal cells could burst
Mechanisms of Passive Transport
•
•
•
•
Solution contains high solute
EX: saltwater
Water moves out of the cell
Cell shrinks (gets dehydrated)
– In plants, cell membrane pulls
away from cell wall
Why would plant
cells be better
off than animal
cells?
What would
happen to the
cells of a
freshwater fish if
it was put into a
saltwater tank?
Mechanisms of Active Transport
• Requires energy (ATP)
• Material flows AGAINST the concentration gradient
– From LOW concentration to HIGH concentration
• Creates a concentration gradient
• Requires protein pumps (need energy to work)
Movement within a cell
• Use ATP energy to move or “pump” material
against a concentration gradient
• Create and maintain a concentration gradient
Movement within a cell
Movement within a cell
•
•
•
•
•
Used to transport very large molecules or food
Requires energy (ATP)
Endocytosis = bringing materials into the cell
Exocytosis = taking materials out of the cell
Cell membrane/vesicles play a role
Movement within a cell
ENDOCYTOSIS
EXOCYTOSIS
VISUAL COMPARISON
• Take a large piece of paper and divide it into 6 parts
• Each section should have a diagram of a mode of
transport
»
»
»
»
»
»
Diffusion
Facilitated Diffusion
Osmosis
Protein Pumps
Endocytosis
Exocytosis
• Things I’m looking for: phospholipid bilayer,
concentration gradients, protein channels/pumps,
ATP, direction of movement
Homeostasis
• Maintaining stability in the cell or body
• Variables within the body can fluctuate
– Temperature, pH, water balance
• Process by which an organism monitors and maintains
a constant state = homeostatic mechanism
Homeostasis
• Negative feedback = maintains homeostasis (like a
thermostat)
• Positive feedback = amplifies a change to the
system
Homeostasis
• Normal body temp = 37oC (98.6oF)
• When body temp is high, we sweat
to release heat
• When body temp is low, we shiver
to generate heat
Keystone Questions
1. Carbon dioxide and oxygen are molecules that can
move freely across a plasma membrane. What
determines the direction that carbon dioxide and
oxygen move?
A.
B.
C.
D.
Orientation of cholesterol in the plasma membrane
Concentration gradient across the plasma membrane
Configuration of phospholipids in the plasma membrane
Location of receptors on the surface of the plasma
membrane
Keystone Questions
2. A sodium-potassium pump within a cell membrane requires
energy to move sodium and potassium ions out of a cell.
The movement of glucose into or out of a cell does not
require energy. Which statement best describes the
movement of these materials across a ac cell membrane?
A. Sodium and potassium ions move by active transport, and
glucose moves by osmosis
B. Sodium and potassium ions move by active transport and
glucose moves by facilitated diffusion.
C. Sodium and potassium ions move by facilitated diffusion and
glucose moves by osmosis
D. Sodium and potassium ions move by facilitated diffusion and
glucose moves by active transport
Keystone Questions
3. Which example is an activity that a fish most uses
to maintain homeostasis within its body?
A.
B.
C.
D.
Using camouflage to avoid predators
Feeding at night to regulate body temperature
Moving to deeper water to regulate metabolic wastes
Exchanging gases through its gills to regulate oxygen
levels.
Keystone Questions
4. Diffusion occurs because
A. Molecules are attracted to one another
B. Molecules constantly move and collide with one
another
C. Cellular energy forces molecules to collide with one
another
D. Cellular energy pumps molecules across the cell
membrane
Keystone Questions
5. During diffusion, when the concentration of
molecules on both sides of the membrane are
equal, molecules will
A. Move across the membrane to the outside of the cell
B. Stop moving across the membrane
C. Continue to move across the membrane in both
directions
D. Move across the membrane to the inside of the cell
Keystone Questions
6. Why is the phospholipid bilayer only partially
permeable to water?
A. Water is repelled by the polar tails of the phospholipid
B. Water is repelled by the polar head of the phospholipid
C. Water is repelled by the hydrophobic tails of the
phospholipid
D. Water is repelled by the hydrophobic head of the
phospholipid
Keystone Questions
7. Which of the following is NOT involved in the
transport of molecules by facilitated diffusion?
A.
B.
C.
D.
ATP
phospholipids
Protein channels
Concentration gradient
Keystone Questions
8. What is one way that facilitated diffusion differs
from simple diffusion?
A.
B.
C.
D.
Facilitated diffusion requires energy input
Facilitated diffusion requires membrane proteins
Facilitated diffusion requires a concentration gradient
Facilitated diffusion requires small, nonpolar molecules
Keystone Questions
9. A pipe carries excess rainwater into a lake. The rainwater
has picked up dissolved nitrates from surrounding lawns.
Which of the following is a consequence of simple diffusion
of the nitrates in the lake?
A. A concentration gradient of nitrates is created and maintained
B. The total amount of dissolved nitrate in the lake water decreases
C. Nitrate concentration decreases in some places and increases in
others
D. Energy is required to move the nitrates from one end of the lake
to the other
Keystone Questions
9. What is a major difference between active and
passive transport?
A. Active transport moves ions, while passive transport
does not
B. Active transport requires energy while passive
transport does not.
C. Active transport involves a concentration gradient
while passive transport does not.
D. Active transport uses membrane proteins while passive
transport does not.
Keystone Questions
10. The human body maintains a constant internal
temperature of 98.6oF. Which changes may occur if body
temperature rises to 100.1oF?
A. Muscle tissue shivers and skin capillaries dilate
B. Perspiration increases and skin capillaries dilate
C. Muscle tissue shivers and skin capillaries constrict
D. Perspiration increases and skin capillaries constrict
Keystone Questions
11. Which is not an example of homeostasis?
A. A jogger stops to drink at a water fountain.
B. A turtle spends hours sitting on a sunny rock
C. A deer seeks out salty foods to add to its diet
D. A rabbit hides among grasses to avoid a hawk