CH 5HOMEOSTASIS 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

Animal Cells (red blood cells)

Plant cells

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=9Ynm5ZOW59Q

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 and Exocytosis http://highered.mcgraw-hill.com/sites/9834

092339/student_view0/chapter5/endocytosis_and_exocytosis.html -

http://www.youtube.com/watch?v=K7yku3sa4Y8

Types of active diffusion

Endocytosis: fluid, macromolecules, or other large particles brought into cell

1. Pouch forms in membrane lipids2. Materials fill pouch3. Pouch pinches in and breaks off from membrane4. Now a vesicle Two types: Pinocytosis: transport of fluids (“cell drinking”) Phagocytosis: large particle transport (“cell

eating”) http://www.youtube.com/watch?v=pvOz4V699gk

&feature=fvwrel

Exocytosis

Process by which a substance is released by a cell

http://www.youtube.com/watch?v=U9pvm_4-bHg