Passive Transport

passive transport

movement of materials in and out of the cell WITHOUT the use of energy in the phospholipid bilayer

materials that cells need to move

move raw materials in and waste products out

essential for proper cell function

three types of passive transport

simple diffusion

facilitated diffusion

osmosis

simple diffusion

movement of molecules from area of high to low conc’n

aka moving along a concentration gradient

movement of molecules in simple diffusion

always in motion

will eventually bump into each other and change direction until they are evenly distributed in a given space

How effective is diffusion over distances?

works well over short distances

What kind of molecules can be transported by diffusion?

can transport small molecules (O2 or CO2) or hydrophobic molecules

requirement for simple diffusion to happen

membrane must be permeable to the substance

7 factors that affect diffusion rates (speeds up process)

1. Concentration Gradient - faster when there’s a greater difference in conc’n

2. Distance - faster over a shorter distance

3. Area - faster when there’s a greater surface area for molecules to move across

4. Temperature - faster when there’s a higher temperature, molecules gain more energy for motion

5. Molecule Size - faster when the molecule size is smaller

6. Molecule Polarity - faster when molecules are non-polar due to the hydrophobic region of the membrane, polar will repel or be slowed down

7. Ion charge - charged molecules/ions do not diffuse passively, won’t cross without energy

facilitated diffusion

diffusion that uses specialized integral protein (protein channels) to allow some molecules to diffuse but not others

helps larger or charged molecules cross efficiently compared to simple diffusion

only small non-polar molecules can easily pass through

relationship of channel or carrier proteins to facilitated diffusion

they are types of integral proteins that help larger, charged or polar molecules move across the membrane

both of them work in slightly different ways and are designated to a specific type

channel proteins

usually ion channels (allows specific charged ions to pass but not others)

may stay open or open and close at specific times to control ion amount

gates may open in response to hormones, electric charge or pressure

carrier proteins

transport large particles that wouldn’t be able to pass

change shape while transporting

slower rate of diffusion that channel proteins

osmosis

diffusion of WATER molecules from high water conc’n to low across a semi-permeable membrane

“water follows salt” saying

water moves from areas where there is high salt conc’n because it wants to dilute it

trying to balance out the conc’n of solutes on both sides

direction of osmosis

depends on the relative conc’n of water molecules on either side of the membrane

types of solutions based on solute conc’n

isotonic, hypotonic, hypertonic

isotonic conditions

when the water and solute conc’n outside the cell is equal to the concentration inside

animal cell = normal shape, plant = wilted or not normal, not an ideal condition

isotonic in relation to dynamic equilibrium

water molecules move in and out at equal rates, no net movement of water

already at dynamic equilibrium

hypotonic condition

solute conc’n inside the cell is greater than outside the cell

water conc’n inside the cell is less than outside the cell

animal cells = burst from lack of cell wall, plant cells = normal

hypotonic in relation to dynamic equilibrium

water will move INTO the cell to achieve equilibrium

cell expands as a result of water flowing in

hypertonic condition

water conc’n inside is less than outside the cell

solute conc’n side is greater than outside

animal cells = shrivel, plant = membrane shrink away from the cell wall

hypertonic in relation to dynamic equilibrium

water moves out of the cell to acheive equilibrium

cell shrinks as a result