1. The Cell Membrane & Homeostasis

2. Cells maintain homeostasis because of the CELL MEMBRANE!!
Homeostasis - The ability to maintain a STABLE internal environment in a changing atmosphere
Cells maintain concentrations of
Water
Glucose
Nutrients
Wastes
Salts
Etc.
Cells maintain homeostasis because of the CELL MEMBRANE!!

3. Cell Membrane CAN cross CAN’T cross
The Cell Membrane regulates what ENTERS and LEAVES the cell and maintains homeostasis
Semi-permeable: only some things can cross the membrane
CAN cross
CAN’T cross
Water
Oxygen
Small molecules
Glucose (too BIG)
Ions
Large molecules

4. Phospholipid Bilayer
Two layers of phospholipids that make a flexible barrier
Fluid Mosaic Model: Allows molecules to move around along the lipid bilayer

5. Cell Membrane
Carbohydrates and Proteins are embedded (enclosed) in the layer
Each part of the membrane has a specific job

6. A – Phospholipid – form the majority of the membrane
B – Hydrophilic Head – “water-loving” - allows polar molecules into/out of the cell
C – Hydrophobic Tails – “water-hating” – allows non-polar molecules into/out of cell
D – Receptor Protein – receive messages (hormones)
MUST fit just like an enzyme
E – Pore Protein – allows water into/out of the cell
F – Ion Channel – allows ions into/out of the cell
G – Glycoprotein – cell recognition “name tag”

7. Movement - Transport
ALL things want to be in BALANCE – EQUAL on both sides
Particles move in response to a concentration gradient

8. Types of Transport ATP Two categories of transport: Passive and Active
Passive Transport: movement of a substance from an area of HIGH concentration to an area of LOW concentration
Uses NO energy!!
How do we flow? HIGH to LOW
ATP

9. Diffusion
Diffusion: PARTICLES move from HIGH to LOW concentration

10. Diffusion
The red particles are moving from an area of HIGH concentration (the baggie in the center) to an area of LOW concentration (the water outside the baggie)

11. Diffusion
This DOES NOT require energy because you are going WITH the concentration gradient.
Like skating down a hill…you don’t have to do any work…it just happens
How do we flow? HIGH to LOW!!

13. Facilitated Diffusion
Facilitated Diffusion (facilitate = HELP): Diffusion of PARTICLES with the help of a protein channel
Moves from HIGH to LOW concentration
Does this need energy? NO

14. Facilitated Diffusion
Help can be a protein channel (the particles just move through) or a carrier protein (it changes shape to allow particles to fit through

15. Osmosis Osmosis: The diffusion of WATER from HIGH to LOW concentration
Does NOT need energy
How do we flow? HIGH to LOW

16. Dynamic Equilibrium
Passive transport results in DYNAMIC EQUILIBRIUM: when the gradient is even on both sides.
Movement still continues but there is NO CHANGE in concentrations

17. Practice Problems What would happen in the picture to the right?
Would this require energy?
Why or why not?
What type of transport is this?

18. Practice Problems
Draw what this beaker would look like after it has reached DYNAMIC EQUILIBRIUM
Did this movement need energy?
Why or why not?
What is this kind of transport called?

19. Practice Problems What is happening in this picture?
Does this need energy?
Why or why not?
What is this type of transport called?

20. Active Transport
Active Transport: a substance can move across the cell membrane AGAINST the concentration gradient with the help of a PUMP
LOW to HIGH concentration
Needs a Protein ‘pump’
Needs ATP (energy)

21. Active Transport

22. Active Transport
This DOES require energy because you are going AGAINST the concentration gradient.
Like skating up a hill…it can happen…you just have to do some work
From LOW to HIGH…you must TRY

24. Hypo, Hyper, Iso? Hypo = LOW Hyper = HIGH Iso = EQUAL
Hypotonic Solution = LOW particles – HIGH water
Hypertonic Solution = HIGH particles – LOW water
Isotonic Solution = EQUAL particle – EQUAL water
TONIC refers to the PARTICLES not the WATER
The WATER is moving…
How do we flow? HIGH to LOW!!

25. Practice Problem
What will happen to this ‘cell’ when it is placed in the 3 beakers shown below?
Beaker A
Beaker B
Beaker C

28. Drink to Death?