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_diffusion_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/biotutorials/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_potassium_pump_works.html