Cell Transport

 The molecules can move freely in the membrane.  They are constantly renewed during a cell's life span.  Grow with the growth of cell and its organelles.  Regenerate to some extent in cases of minor disruptions.  Contract and expand during cell movements.  Allow interactions of cells such as recognition of self and fusion of cell.  Regulate the flow of materials passing through them. These properties indicate that biomembranes are fluid and dynamic.

 Fluid - highly viscous fluid  Mosaic = matrix of…  Bilayer of phospholipids  Globular proteins embedded ▪ Channel proteins (doorways) ▪ Marker proteins (name badge) ▪ Receptor proteins (on/off switch)

 The membrane is only as good as its parts  Phospho- portion is polar and attracts  -lipid portion is nonpolar and repels  Jobs:  Acts as a barrier  Transports materials  Transfers materials  Processes materials

Why does too much fertilizer burn your lawn? Inside the cell membrane

 The amount of a substance per volume is the concentration  The concentration of molecules ranges from high to low, hence gradient.  But molecules  are in constant motion  collide into & bounce off of one another  eventually spread out evenly = equilibrium

 maintain a constant internal conditions (homeostasis)  respond to their environment (the concentration gradient)  balance between inside and outside concentrations occurs to create equilibrium  molecules are transported into the cell if there’s more outside the cell  molecules are transported out of the cell if there’s more inside the cell

 Passive Transport  Simple diffusion (solute)  Facilitated diffusion (with help)  Osmosis (water)  Molecules move with the concentration gradient (from high to low)  Requires no energy

Carrier or channel proteins help large molecules to diffuse from high to low

 Water movement from high to low concentrations  Osmotic pressure is the force exerted on the cell membrane from the water found on either side of the cell membrane  Osmotic (water) pressure gives plant cells turgidity (crisp veggies vs. soggy)

When is equilibrium reached in a solution?  When equal concentrations of molecules are found throughout the solution or on either side of a semi- permeable membrane, like that of a cell.

 Active transport – move against gradient (from low to high )  Sodium-potassium pump  Endocytosis (cell eating – think PacMan) to form vacuoles  Exocytosis (cell pooping) to rid cells of waste

 The [concentration] of dissolved solutes inside/outside of the cell.  Start by determining the concentration of solutes found inside the cell.  Then determine the concentration of solutes found outside the cell.  Compare the two.

 concentration of dissolved solutes is equal to cell contents  Cell is in equilibrium with its environment  No net movement of solutes or water in either direction  Molecules are still moving but equally in BOTH directions

 Concentration of dissolved solutes is greater than cell contents  Water moves out  Cell size shrinks = “skinny” cell

 concentration of dissolved solutes is less than cell contents  Water moves in and solute moves out  Cell size swell/increase = “hippo-fat” cell