Cellular Transport CH 2.1 Mr. Traub

Osmosis: Diffusion of Water Osmosis: diffusion of water across a selectively permeable membrane depending on the concentration of solutes on either side of the membrane Diffusion: movement of particles from an area of higher concentration to an area of lower concentration Important factor in maintaining homeostasis

Osmosis In Action Before Osmosis After Osmosis

What Just Happened? Two solutions separated by a selectively permeable membrane, only allows water to diffuse across Water flows to side of the membrane where water has low concentration. (High to Low) Water diffuses until it has equal concentration on both sides of the membrane Therefore, an unequal distribution of particles is called a concentration gradient

How Osmosis Affects Cells Most cells, whether in multicellular or unicellular organisms, are subject to osmosis because they are surrounded by water solutions. Three types of solutions that cells may be in; Isotonic solution Hypotonic solution Hypertonic solution

Isotonic Solution Solute concentration of solution and water equal to that of cell Water molecules move in and out at the same rate, so cell maintains shape

Hypotonic Solution Solute concentration of solution lower than cell Less dissolved particles outside of cell than inside of cell More water outside the cell than inside Hypo = less, under (think hypodermic, hypothermia); Tonic = dissolved particles Cell expands (and may burst)

Hypertonic Solution Solute concentration of solution higher than cell More dissolved particles outside of cell than inside of cell Hyper = more (think hyperactive); Tonic = dissolved particles Water moves out of cell into solution Cell shrinks

Other Types of Cellular Transport Passive Transport Active Transport

Passive Transport Cell uses no energy to move particles Transport proteins, carrier proteins, and channel proteins help substances move through the plasma membrane This is known as Facilitated diffusion

Facilitated Diffusion Allows diffusion of large, membrane insoluble compounds such as sugars and amino acids Does not require energy (passive) Highly Selective Substance binds to membrane-spanning transport protein Binding alters protein conformation, exposing the other surface Fully reversible - molecules may enter the cell and leave the cell through the transport protein. Particles move from areas of high concentration to areas of low concentration.

Active Transport Move particles from region of lower concentration to region of higher concentration Requires energy from the cell Carrier protein binds with particle of substance to be transported, chemical energy allows cell to change shape of carrier protein and particle is released on other side of membrane

Passive & Active

Transport of Large Particles Endocytosis: process by which a cell surrounds and takes in material from its environment Exocytosis: expulsion of materials from the cell Ex: expel waste, secrete hormones

Endocytosis & Exocytosis

Review http://www.wiley.com/legacy/college/boyer/0470003790/animations/membrane_transport/membrane_transport.htm