1. Cell Membrane & Transport
Unit 2: The Cell

2. Types of Outer Cell Boundaries:
CELL WALL
outer boundary found in plant cells, bacteria, fungi, some protists
Thick and inflexible
Function: Provides support for plant cell
Never found in animal cells

3. Cell (Plasma) Membrane
Thin, flexible barrier between cell & environment (All cells)
Selectively permeable
Functions:
Controls movement in and out of cell
Allows cell recognition; boundary for cell
Maintains homeostasis: balance within the cells

4. Fluid Mosaic Model
The fluid mosaic model states that the cell membrane is a lipid bilayer made up of molecules which are free to move.
Phospholipids: fatty areas that attract and repel water causing the membrane to behave like a fluid
Hydrophilic heads (Polar): close to water as possible
Hydrophobic tails (Non-polar): far away from water as possible
Animation:

5. Embedded Proteins Determine which particles can pass through
Serve as recognition markers
Form channels from one side of the cell to the other
Used in facilitated diffusion

6. Movement Across the Membrane
PASSIVE Transport: requires no energy, movement from HIGH to LOW concentration
* Examples: diffusion, osmosis
*No Energy required
ACTIVE Transport: requires energy, movement from LOW to HIGH concentration
* Examples: endocytosis, exocytosis
*Energy required! ATP

7. Types of PASSIVE Transport
Movement WITH the concentration gradient
DIFFUSION: movement of particles from high concentration to low concentration
Causes substances to move across membrane
Does not require the cell to use energy
Substances move across membrane until both sides are equal (EQUILIBRIUM)

8. OSMOSIS: diffusion of water through a membrane
water moves from where there is a lot to where there is a little until it reaches equilibrium
exerts pressure (OSMOTIC PRESSURE) which can cause cell swelling
Higher Concentration
of Water
Water molecules
Lower Concentration
of Water
Sugar molecules

9. Diffusion may be:
FACILITATED
Process by which proteins in the membrane help substances enter the cell
Protein channels are SPECIFIC only allowing some things in/out
Movement from HIGH to LOW

10. Types of ACTIVE Transport
Movement AGAINST the concentration gradient
Energy required
ENDOCYTOSIS: cells ingest external fluid, macromolecules, and large particles
Phagocytosis: cell takes in food
Pinocytosis: cell takes in water
EXOCYTOSIS: cells remove fluids, macromolecules and large particles

11. HYPERTONIC: concentration is higher inside the cell than outside (water)
HYPER means “above strength”
Water moves OUT of cell causing it to shrivel
Can result in PLASMOLYSIS in plants which causes wilting
TYPES OF SOLUTIONS

12. ISOTONIC: solution where concentrations of dissolved substances outside the cell is the same as the inside of the cell
ISO- means “equal to”
Movement into cell= movement out of cell

13. HYPO means “below strength”
HYPOTONIC: concentration of water is higher outside the cell than inside
HYPO means “below strength”
Water will move INTO cell causing it to swell
Cells could rupture if the cell takes in too much water
This increases pressure inside of cell (TURGOR PRESSURE)
Animation:

16. Hippo Hypo