Transport In and Out of the Cell

How Diffusion Works

• A little video

• Video

Diffusion

• This is also known as passive transport

and simple diffusion

• Passive transport is the movement of

molecules down a concentration gradient

from a region of higher concentration to

lower concentration.

• Passive transport NEVER requires energy.

(ATP)

• The steeper the gradient, the faster the rate of

diffusion.

• Humans obtain oxygen by simple diffusion

across moist membranes in the air sacs in our

lungs called alveoli.

Diffusion

• It is also affected by

– Temperature- the higher the temp. the faster

the molecules are moving

– Size of the Molecules- the bigger the

molecule is the harder it is to pass through the

membrane, possible not pass at all.

How Osmosis Works

• http://highered.mcgraw-

hill.com/sites/0072495855/student_view0/

chapter2/animation__how_osmosis_works

.html

Osmosis

• Osmosis- the diffusion of water (across a membrane)

• Water will move in the direction where there is a high concentration of solute (and hence a lower concentration of water.

• Salt is a solute, when it is concentrated inside or outside the cell, it will draw the water in its direction. This is also why you get thirsty after eating something salty.

SALT SUCKS

Isotonic Solution

• If the concentration of

solute (salt) is equal

on both sides, the

water will move back

in forth but it won't

have any result on the

overall amount of

water on either

side."ISO" means the

same

Hypotonic Solutions

• The word "HYPO" means less, in this case there are less solute (salt) molecules outside the cell, since salt sucks, water will move into the cell.

• The cell will gain water and grow larger. In plant cells, the central vacuoles will fill and the plant becomes stiff and rigid, the cell wall keeps the plant from bursting

Hypertonic Solutions

• The word "HYPER"

means more, in this case

there are more solute

(salt) molecules outside

the cell, which causes the

water to be sucked in that

direction.

• In plant cells, the central

vacuole loses water and

the cells shrink, causing

wilting.

Hypertonic Solution

• In animal cells, the cells also shrink

• This is why it is dangerous to drink sea

water - its a myth that drinking sea water

will cause you to go insane, but people

marooned at sea will speed up

dehydration (and death) by drinking sea

water.

How Facilitated Transport Works

• A little video to show you

• http://highered.mcgraw-

hill.com/sites/0072495855/student_view0/

chapter2/animation__how_facilitated_diffu

sion_works.html

Facilitated Diffusion

• Facilitated diffusion relies on special protein

channels to assist in transporting specific

substances across membranes.

Facilitated Diffusion

• The proteins helps or facilitated the diffusion by changing shape and moving the molecule down the concentration gradient.

• This is very similar to diffusion in that both involve the movement of molecules down the concentration gradient with out energy

– They differ in the fact that this needs special proteins (carrier proteins)

Dynamic Equilibrium

• When the rates of the forward and reverse reactions are equal. The system is dynamic because individual molecules react continuously. It is at equilibrium because no net change occurs.

All of the previous

require

NO ENERGY or

ATP

Active Transport

• This is the movement of molecules against

a gradient.

– This is like driving a car in traffic, going in the

wrong direction. It takes more energy to go

against the path then it does to go with the

traffic.

• This requires ENERGY, ATP.

Active Transport

• Active transport occurs with the aid of

carrier proteins, which are commonly

known as pumps.

• The cell maintains the proper balance of

substances it needs due to this active

transport.

• This helps maintain homeostasis.

Endocytosis

• This is the process by which a cell surrounds a

substance in the outside environment, enclosing

it in a portion of the plasma membrane.

• The membrane pinches off and leaves the

substance inside the cell and the resulting

vacuole, with the contents moves to the inside of

the cell.

• http://www.coolschool.ca/lor/BI12/unit4/U04L05/

endocytosis_final.html

Exocytosis

• This is the active release of molecules from a cell. This is the opposite of endocytosis.

• The cell uses this to get rid of wastes and to secrete substances, for example hormones, produced by the cell.

• http://www.coolschool.ca/lor/BI12/unit4/U04L05/exocytosis.html

Pinocytosis

• This is also called cell drinking.

• This is the uptake of large dissolves

molecules.

• The plasma membrane surrounds

small/tiny particles and encloses them in a

vesicle.

• http://student.ccbcmd.edu/~gkaiser/biotuto

rials/eustruct/pinocyt.html

Phagocytosis

• This is the engulfing of large particles or

even small organisms by pseudopods.

• The cell membrane wraps around the

particles and encloses them forming a

vacuole.

• This is the way that the human white blood

cells take up bacteria.

• PAC-MAN

Receptor-Mediated Endocytosis

• This enables cells to take up large

amounts of very specific substances.

• The extra cellular substances bind to

specific on the cell membrane and are

brought into the cell.

– Example: This is the way that body draws the

cholesterol into the blood.

• Membrane pumps carry particles or ions

across the membranes AGAINST the

gradient (needs energy/ATP).

• The sodium-potassium pump is an

example of this

Sodium - Potassium Pumps

• This is one of the most common active transport

pumps.

• This is found in the plasma (cell) membrane of

animal cells.

• This maintains the levels of Sodium (Na) and

Potassium (K) in and out of the cell

• This protein pump uses the energy in order to

transport 3 sodium ions out of the cell while

moving 2 potassium ions into the cell.

• http://highered.mcgraw-

hill.com/sites/0072495855/student_view0/

chapter2/animation__how_the_sodium_po

tassium_pump_works.html