Ch 5 Homeostasis and cell transport

How do cells get the things they need? How do they get rid of their wastes? How do cells transport stuff?

5-1 Passive transport Materials must be able to cross the cell membrane Some don’t require energy input: Passive transport Diffusion: movement of particles from area of high to low concentration

Diffusion Two solutions can have different concentrations of solute (particles) Concentration gradient: the difference in concentration of molecules Diffusion driven by kinetic energy Molecules are in constant motion Diffusion occurs until equilibrium is reached

Diffusion across membranes Diffusion across a membrane is called simple diffusion Not everything can diffuse through a membrane Limits include Size polarity

Osmosis Osmosis: process by which water molecules diffuse across a membrane from an area of high to low concentration Form of passive transport Direction of movement depends on relative concentration of solutes in solution

Direction of osmosis If concentration of solutes outside of cell is lower than inside the cell, the solution outside is hypotonic Water diffuses into cell Animal cells can lyse (burst) If concentration of solutes outside the cell is higher than inside, the solution outside is hypertonic Water diffuses out of cell Plasmolysis (cell shrinks) When concentrations are equal: isotonic Equal movement into and out of the cell

More osmosis stuff Turgor pressure: pressure that water exerts against plant cell wall Page 99: contractile vacuoles: remove excess water http://www.youtube.com/watch?v=9Ynm5ZOW59 Q

Facilitated diffusion Passive diffusion Molecules cross cell membrane through transport proteins

Active transport Movement of substances from low to high concentrations Against the concentration gradient Requires energy

Types of active diffusion Endocytosis: fluid, macromolecules, or other large particles brought into cell Pouch forms in membrane lipids Materials fill pouch Pouch pinches in and breaks off from membrane Now a vesicle Two types: Pinocytosis: transport of fluids Phagocytosis: large particle transport http://www.youtube.com/watch?v=pvOz4V699gk&featur e=fvwrel

Exocytosis Process by which a substance is released by a cell http://www.youtube.com/watch?v=U9pvm_4-bHg http://www.youtube.com/watch?v=K7yku3sa4Y8