Cell Transport All cells must maintain HOMEOSTASIS (balance). What types of substances must be balanced in a cell?

First Step: Cell Membrane Cell membrane is semi- or selectively permeable – not all molecules can pass through. http://micro.magnet.fsu.edu/cells/animals/images/plasmamembrane.jpg

Concentration gradient The difference in concentration of a given molecule between two points is called the concentration gradient. The larger the gradient, the greater the net movement of the molecules. Molecules continue to move until evenly distributed (gradient = 0).

Diffusion Diffusion occurs whenever molecules move from areas of high concentration to low concentration. The movement is caused by the random kinetic energy of the molecules, so does not require any energy input. http://www.biologycorner.com/bio1/diffusion.html

Passive Transport Does not require energy. Molecules move from high concentration to low concentration. Three major types: Simple Diffusion Osmosis Facilitated Diffusion Slide by D Regelski Image: www.mcs.kent.edu/~gbarrick/ journls/birding.html

Simple Diffusion across a Membrane Molecules pass directly through lipid bilayer. Molecules generally small with little or no electrical charge (O2, CO2, H2O, etc.). http://www.emc.maricopa.edu/faculty/farabee/BIOBK/6_5a.jpg

Facilitated Diffusion Molecules move through special proteins. Move from high concentration to low. Does not require energy. http://www.biology.arizona.edu/chh/problem_sets/kidneysmetals/graphics/channel.gif

Osmosis Special type of diffusion. Involves water moving across a selectively permeable membrane. Very important in living organisms. http://www.biologycorner.com/resources/osmosis.gif

Tonocity During osmosis, water moves from high concentration to low concentration. Water is called a solvent, molecules dissolved in water are called solutes. There are three terms to describe the direction in which water molecules will move during osmosis: Hypotonic Isotonic Hypertonic

Hyper- and Hypotonic Hypo = less solute Hyper = more solute These are relative terms like “greater than” or “less than” Water moleclue http://waynesword.palomar.edu/images/osmosi2.gif Solute molecule

Effects of Tonicity on Cells http://www.connect.ab.ca/~lburns/osmosis.gif

Active Transport Moves molecules against their gradient (from low to high concentration). This requires energy. Two major types: Carrier Proteins Endocytosis

Carrier Proteins Special membrane proteins that use energy to move molecules across the membrane. http://www.sirinet.net/~jgjohnso/activetrans1.jpg

Endocytosis Process by which large molecules or large volumes of liquid are taken into cells. Endo- means inside, cytosis refers to cell Phagocytosis = “cell eating” Pinocytosis = “cell drinking” Requires energy.

Phagocytosis Cell membrane folds around and brings particle into cell. The membrane around the particle pinches off and forms a vesicle. The vesicle will eventually fuse with a lysosome for digestion. http://academic.brooklyn.cuny.edu/biology/bio4fv/page/endoc.gif

Pinocytosis Cell membrane folds around and brings liquid into cell. The membrane around the liquid pinches off and forms a vesicle. http://www.cat.cc.md.us/courses/bio141/lecguide/unit1/eustruct/images/pinocyt.gif

Exocytosis The opposite of endocytosis is called exocytosis (exo = outside). This is what happens to the packages produced by the Golgi bodies that leave the cell. http://www.cat.cc.md.us/courses/bio141/lecguide/unit2/viruses/relexo.html Cell Membrane