homeostasis and transport a4. a4. homeostasis and transport 1.describe how the structure of the...
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HOMEOSTASIS and TRANSPORT
A4
A4. Homeostasis and Transport1. 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 lipid bilayerphospholipid impermeableselectively permeable protein channelprotein pump osmosisdiffusion facilitated diffusionactive transport passive transportendocytosis exocytosisisotonic equilibriumhypertonic concentration gradienthypotonic homeostasis
Cell Membrane Structure and function
• Cell membranes are composed of phospholipids• Phospholipids are arranged in two layers (bilayer)• Each phospholipid has a “head” and two “tails”– The head loves water (hydrophilic)– The tails hate water (hydrophobic
• The lipid bilayer is flexible but strong
A phospholipid bilayer
Cell Membrane Structure and FunctionDRAW THIS
in your NOTES!!
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
Fluid Mosaic Model
Cell Membrane Structure and Function
• Barrier between the cytoplasm and the environment
• Protects and supports the cell• Controls everything that enters and leaves the
cell
Functions of the Cell Membrane
Cell Membrane Structure and Function
Membranes are selectively permeable • Some things can cross the membrane (permeable)– Gases, water, small particles
• Some things can cross the membrane with the help of a protein channel or pump– Ions, proteins, large particles
• Some things can’t cross the membrane (impermeable)
Permeability
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?
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 (difference)– Concentration = relative amount of substance
• SUBSTANCE moves from HIGH concentration (of
substance) to LOW concentration (of substance)
• Some materials can pass freely, other materials need a protein channel
Passive Transport Defined
Mechanisms of Passive Transport
Passive Transport is like…
A ball rolling down a hill
Mechanisms of Passive Transport
• Passive transport• Depends on a concentration gradient– Concentration = relative amount of substance– Gradient = difference
• MOVEMENT from HIGH concentration to LOW concentration–Down the concentration gradient
1. Diffusion (a.k.a. simple diffusion)
Mechanisms of Passive Transport
• Passive – requires NO energy• Depends on a concentration gradient (difference)– Concentration = relative amount of water
• MOVEMENT from HIGH concentration to LOW concentration
• just like simple diffusion EXCEPT needs a protein channel
2. Facilitated Diffusion
Mechanisms of Passive Transport
• Diffusion of water• WATER moves from HIGH concentration (of water) to
LOW concentration (of water)
• Aquaporins = protein channels for water to pass• Plays a role in maintaining homeostasis (water balance)
3. Osmosis
Osmosis
Which way will the water molecules move?
Why wouldn’t the green or purple molecules move?
Mechanisms of Active Transport
• Requires energy• Material flows AGAINST the concentration
gradient– From LOW concentration to HIGH concentration
• Requires protein pumps (need energy to work)
Defined
Movement within a cell
• Use ATP energy to move or “pump” material into an area that already has a high concentration
• It’s like pumping air into a basketball
1. Protein Pumps
Movement within a cell
1. Protein Pumps
Movement within a cell
• Used to transport very large molecules or food• Endocytosis = bringing materials into the cell• Exocytosis = taking materials out of the cell• Cell membrane/vesicles play a role
2. Bulk Transport
Movement within a cell
2. Bulk Transport
Homeostasis
• Maintaining stability in the cell or body• Variables within the body can fluctuate– Temperature, pH, water balance
• Important to maintain homeostasis near set point• Cell membrane aids in maintaining homeostasis
Defined
Homeostasis
• Diffusion of water• Passive (no energy required)• Water will move across the membrane down its
concentration gradient• Cell membrane regulates the amount of water
inside a cell
Osmosis and water balance
Homeostasis
• 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
ISOTONIC Conditions
Homeostasis
• Amount of solute surrounding cell is high (high solute = low water)
• Water moves out of the cell to balance concentrations of water on both sides of membrane
• Cell shrinks (dehydrates)• EX: saltwater
HYPERTONIC Conditions
Homeostasis
• Amount of solute surrounding cell is low (low solute = high water)
• Water moves INTO the cell to balance concentrations of water on both sides of membrane
• Cell swells (animal cells could burst)• EX: pure water
Hypotonic conditions
Homeostasis
Osmosis
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?
Cell Transport Review
• Divide your poster into six sections• In each section, diagram one of the following
modes of transport– Simple diffusion– Facilitated diffusion– Osmosis– Active transport via protein pumps– Exocytosis– endocytosis
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. Orientation of cholesterol in the plasma membraneB. Concentration gradient across the plasma membraneC. Configuration of phospholipids in the plasma membraneD. 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. Using camouflage to avoid predatorsB. Feeding at night to regulate body temperatureC. Moving to deeper water to regulate metabolic wastesD. Exchanging gases through its gills to regulate oxygen
levels.
Keystone Questions
4. Diffusion occurs becauseA. Molecules are attracted to one anotherB. Molecules constantly move and collide with one
anotherC. Cellular energy forces molecules to collide with one
anotherD. 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 cellB. Stop moving across the membraneC. Continue to move across the membrane in both
directionsD. Move across the membrane to the inside of the cell