1. HOMEOSTASIS and TRANSPORT

2. A4. Homeostasis and Transport
Describe how the structure of the plasma membrane allows it to function as a regulatory structure and/or protective barrier for a cell.
Compare the mechanisms that transport materials across the plasma membrane.
Explain how organisms maintain homeostasis.
Describe how membrane-bound organelles facilitate the transport of materials within a cell.

3. A4. Vocabulary
plasma membrane lipid bilayer phospholipid impermeable selectively permeable protein channel protein pump osmosis diffusion facilitated diffusion active transport passive transport endocytosis exocytosis isotonic equilibrium hypertonic concentration gradient hypotonic homeostasis

4. Cell Membrane Structure and function
A phospholipid bilayer
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

5. Cell Membrane Structure and Function
DRAW THIS in your NOTES!!

6. Cell Membrane Structure and Function
Fluid Mosaic Model
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

7. Cell Membrane Structure and Function
Functions of the Cell Membrane
Barrier between the cytoplasm and the environment
Protects and supports the cell
Controls everything that enters and leaves the cell

8. Cell Membrane Structure and Function
Permeability
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)

9. 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?

10. Can you do it?
Give as many names for the boundary of the cell as you can…

11. Mechanisms of Passive Transport
Passive Transport Defined
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

12. Mechanisms of Passive Transport
Passive Transport is like…
Create an analogy…
The hill is like the concentration gradient
The ball is like a molecule moving down its gradient
In a cell this gradient has to do with concentration of materials on either side of the membrane
A ball rolling down a hill

13. Mechanisms of Passive Transport
1. Diffusion (a.k.a. simple diffusion)
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

15. Mechanisms of Passive Transport
2. Facilitated Diffusion
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

17. Mechanisms of Passive Transport
3. Osmosis
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)

18. Which way will the water molecules move?
Osmosis
Which way will the water molecules move?
Why wouldn’t the green or purple molecules move?

19. Mechanisms of Active Transport
Defined
Requires energy
Material flows AGAINST the concentration gradient
From LOW concentration to HIGH concentration
Requires protein pumps (need energy to work)

20. 1. Protein Pumps 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

21. Movement within a cell
1. Protein Pumps

22. 2. Bulk Transport 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

23. Movement within a cell
2. Bulk Transport

25. Defined 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

26. Osmosis and water balance
Homeostasis
Osmosis and water balance
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

27. ISOTONIC Conditions 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

28. HYPERTONIC Conditions
Homeostasis
HYPERTONIC Conditions
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

29. Hypotonic 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

30. Homeostasis
Osmosis

31. Why would plant cells be better off than animal cells
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?

32. 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

33. Keystone Questions
Carbon dioxide and oxygen are molecules that can move freely across a plasma membrane. What determines the direction that carbon dioxide and oxygen move?
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

34. Keystone Questions
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?
Sodium and potassium ions move by active transport, and glucose moves by osmosis
Sodium and potassium ions move by active transport and glucose moves by facilitated diffusion.
Sodium and potassium ions move by facilitated diffusion and glucose moves by osmosis
Sodium and potassium ions move by facilitated diffusion and glucose moves by active transport

35. Keystone Questions
Which example is an activity that a fish most uses to maintain homeostasis within its body?
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.

36. Keystone Questions 4. Diffusion occurs because
Molecules are attracted to one another
Molecules constantly move and collide with one another
Cellular energy forces molecules to collide with one another
Cellular energy pumps molecules across the cell membrane

37. Keystone Questions
During diffusion, when the concentration of molecules on both sides of the membrane are equal, molecules will
Move across the membrane to the outside of the cell
Stop moving across the membrane
Continue to move across the membrane in both directions
Move across the membrane to the inside of the cell