Passive Transport Where are membranes found? Cell Organelles

Passive Transport

Where are membranes found?

• Cell• Organelles

Cell Membrane

• Allows certain things to enter and leave

• Phosphate head• Lipid tail

• Two layers

a.k.a. semipermeable phospholipid bilayer

High Concentration Low Concentration

Concentration– amount of substance in

a given volume

Passive

Passive Transport

•Movement of materials that DOES NOT require energy (ATP)

Passive

Passive Transport

Diffusion

Pas

sive

Tran

sport

High Concentration

Low Concentration

Diffusion

• Move from HIGH to LOW concentration– “passive transport”– no energy needed

diffusion osmosis

movement of water

Diffusion across cell membrane

• Cell membrane is the boundary between inside & outside…– separates cell from its environment

IN: foodcarbohydratessugars, proteinsamino acidslipidssalts, O2, H2O

OUT: wasteammoniasaltsCO2

H2O products

IN

OUT

Diffusion• Continues until an equilibrium is

reached– Equilibrium – balanced; equally

distributed

• What will happen when dye is added to a beaker of water?

a

b

c

What causes diffusion?

• Movement of molecules– As they move they bump into each

other

• Collisions cause molecules to move away from each other

– http://www.stolaf.edu/people/giannini/flashanimat/transport/diffusion.swf

Factors Affecting Diffusion

•Temperature—the higher the temperature, the faster diffusion occurs

•Molecular Size—the bigger the molecule, the longer diffusion takes

Osmosis

Passive

Passive Transport

Diffusion

Osmosis

• Diffusion of water across a selectively permeable membrane.

• Occurs until concentration is balanced on both sides of the membrane.

Osmosis is diffusion of water

• Direction of osmosis is determined by comparing total solute concentrations– Hypertonic - more

solute, less water

– Hypotonic - less solute, more water

– Isotonic - equal solute, equal water

Hypertonic

• Medium has more solute than the cell

• More water leaves the cell than enters it

• Cell will shrink

Hypotonic

• The medium has less solute than the cell

• More water enters the cell

• The cell will swell

Isotonic• Medium is exactly

the same solute concentration as the cell

• Amount of water moving in equals water going out

• The cell will stay the same size

What is happening here?

Osmosis

Passive

Passive Transport

Diffusion

Facilitated Diffusion

Isnt the membrane “semi-permeable”?

• What molecules can get through directly?– fats & other lipids

inside cell

outside cell

lipid

salt

aa H2Osugar

NH3

What molecules can NOT get through directly?

polar molecules

H2O ions

salts, ammonia large molecules

starches, proteins

Channels through cell membrane

• Membrane becomes semi-permeable with protein channels – specific channels allow specific

material across cell membrane

inside cell

outside cell

sugaraaH2O

saltNH3

Facilitated Diffusion

• Diffusion through protein channels– channels move specific molecules across

cell membrane– no energy needed

“The Bouncer”“The Bouncer”

open channel = fast transport

facilitated = with help

high

low

Active Transport• Cells may need to move molecules against

concentration gradient– shape change transports solute from

one side of membrane to other – protein “pump”– “costs” energy = ATP

ATP

low

high

Active Transport

ATP ATP

How about large molecules?

• Exocytosis– Through

vesicles & vacuoles

– “Exit Cell”

Endocytosis

• Endocytosis– phagocytosis

= “cellular eating”

– pinocytosis = “cellular drinking

Review

?

Review

Getting through cell membrane

• Passive Transport– Simple diffusion

• diffusion of nonpolar, hydrophobic molecules– lipids– high low concentration gradient

– Facilitated diffusion• diffusion of polar, hydrophilic molecules• through a protein channel

– high low concentration gradient

• Active transport– diffusion against concentration gradient

• low high

– uses a protein pump– requires ATP

ATP

Transport summarysimplediffusion

facilitateddiffusion

activetransport

ATP

Any Questions??