Cell transport: Diffusion and Osmosis Biology 11

Vocab: Solute =a substance that is dissolved in another substance, thus forming a solution. (ie. salt, sugar) Solvent = a substance, usually a liquid, in which other substances are dissolved, thus forming a solution. (ie. Water)

Types of Membranes: Permeable: allows all (or most) things to cross Selectively (semi-permeable) membrane: allows some things to cross but not others (ie. water can cross but solutes like salt and sugar can NOT) Impermeable membrane: does NOT allow anything to cross

Transport- Passive or Active Passive transport: the movement of materials across a cell membrane without the expenditure of cell energy Active transport: the use of cell energy to move materials across a cell membrane (against concentration gradient)

PASSIVE TRANSPORT From high to low concentration Does not require energy from the cell Includes: Diffusion Osmosis Facilitated diffusion

ACTIVE TRANSPORT From low to high concentration Requires energy from the cell Active transport proteins Endocytosis Exocytosis

DIFFUSION The NET movement of particles from an area of high concentration to an area of low concentration

What is a concentration gradient? Concentration Gradient the difference in concentration of solutes in a given space Diffusion happens when substances move “down” a concentration gradient (from high to low) until the concentration of the two areas becomes equal.

Dynamic Equilibrium At dynamic equilibrium there is no NET movement of particles. DYNAMIC implies movement EQUILIBRIUM implies a balance No longer a concentration gradient Particles move equally in all directions

Dynamic Equilibrium NOTE: At D.E. particles are still moving, its just that overall, they will remain “mixed” unless acted upon by another force. (So no “net” movement overall).

Diffusion Diffusion will always be from an area of ___________ concentration to an area of ____________ concentration. It will continue until _______________ _______________ is reached. HIGH LOW DYNAMIC EQUILIBRIUM

Diffusion Animations http://www.youtube.com/watch?v=qBig2wevHhw http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

OSMOSIS The diffusion of WATER across a semi-permeable membrane.

Osmosis Animations http://www.biology.ualberta.ca/facilities/multimedia/uploads/alberta/dif.html

What is the difference between diffusion and osmosis? Osmosis is just a “special case of diffusion”. It is the diffusion of water across a selectively permeable membrane. Diffusion is the NET movement of particles from an area of high concentration to an area of low concentration!”

ENDOCYTOSIS Cells surround and takes in material from the environment forming a vesicle or vacuole. Includes pinocytosis and phagocytosis

Pinocytosis: Water and dissolved substances are taken up by the cell “cell drinking”

Phagocytosis: Up take of large particles by cells

EXOCYTOSIS Vesicles from the inside of the cell fuse with the plasma membrane and release material on the outside of a cell.