Download Chapter 5 - Homeostasis and Transport I. Passive Transport (no

Chapter 5 - Homeostasis and Transport
I. Passive Transport (no energy from cell required)
A. Diffusion
1. movement of molecules from an area of higher concentration
to an area of lower concentration
a. due to kinetic energy the molecules possess (molecules
in constant motion) – Brownian movement
b. concentration gradient - difference in conc. of molecules
across a space
2. motion random and in straight line so molecules move
“down” conc. gradient from more conc. to less conc.
3. equilibrium - conc. of molecules equal throughout the space
occupied (random movement continues - no conc. grad.)
http://www.youtube.com/watch?v=7alxEBpa4jI
B. Diffusion across membranes
1. membrane selectively permeable (semipermeable)
2. diffusion depends on size and type of molecule
a. nonpolar sub. diffuse through lipid layers (CO2, O2) –
think of nonpolar fatty acid chains
b. polar sub. move through pores made by proteins
3. Dialysis
a. diffusion of solutes across membrane
C. Osmosis
1. diffusion of water through a selectively permeable membrane
from area of higher concentration to an area of lower
concentration
2. cell has no control of this (movement depends on rel. conc. of
solutes on two sides of membrane)
3. hypotonic solution
a. conc. of solutes lower outside cell than inside (solution
outside is hypotonic to cell)
b. water diffuses into cell (gains water)
c. freshwater protozoans
1) contractile vacuole - removes excess water (active
transport)
d. freshwater fish
1) kidneys remove excess water gained through gills
e. plants
1) turgor pressure - as water diffuses in, cell swells,
water molecules exert pressure against cell wall (plant
rigid)
f. cytolysis - bursting of a cell that can’t remove water
4. hypertonic solution
a. conc. of solutes higher outside cell than inside (solution
outside is hypertonic to cell)
b. water diffuses out of cell (loses water)
c. plasmolysis - loss of water by cell in hypertonic sol.
(cell shrivels)
http://www.youtube.com/watch?v=gWkcFU-hHUk
d. humans can’t drink seawater (dehydrate cells)
e. marine fish
1) excrete salt through gills and urine very conc.
f. marine birds and turtles
1) salt excreting gland near eyes
5. isotonic solution - conc. of solutes outside and inside cell are
equal (outside solution isotonic to cell)
a. diffusion in and out equal (no net movement of water)
D. Osmotic Pressure
1. pressure required to stop osmosis into a solution
a. pressure that builds up as water diffuses into a cell
2%
2. If a physical barrier (membrane) prevents expansion of a
hypertonic solution as water moves in by osmosis, then
5%
there is a buildup of pressure as water molecules continue
to move across the membrane.
2%
a. As pressure increases, the net flow of water molecules will
slow (will stop in plants due to cell wall - turgor pressure)
5%
3. Osmotic potential
6%
a. the tendency of water to move across a membrane into a
3%
solution
high O. pot. b. the lower the solute concentration, the higher the osmotic
potential
E. Facilitated Diffusion
1. movement of molecules that don’t diffuse easily across membrane
by specific proteins in membrane (carrier proteins)
a. follows conc. gradient - passive
2. molecule binds to carrier - carrier changes shape - molecule
shielded from lipids and goes through - released
a. speeds up glucose transport
b. carrier molecules are specific in what they carry
3. ion channels- for ions to move through - specific for certain ions
II. Active Transport
(move molecules against conc. gradient - cell must expend energy) (uses
carrier proteins)
A. Cell membrane pumps
1. Sodium-Potassium Pump (Na+ most conc. outside, K+
inside)
a. 3 Na+ from cell interior bind to carrier
b. carrier splits phosphate from ATP
c. phosphate bonds to carrier (energy to change carrier
shape)
d. Na+ carried across and released (outside cell)
e. carrier now has shape to bind to 2 K+ outside cell
f. phosphate released
g. carrier changes shape
h. K+ carried through to inside and released cycle repeats
itself
B. Endocytosis and Exocytosis (transport of macromolecules and
food particles too large to pass through cell membrane)
1. Endocytosis
a. cells ingest materials by membrane surrounding and
forming a pouch
1) pinches off and called a vesicle (lysosomes may
fuse to it)
b. Types
1) pinocytosis - transport of solutes or fluids
2) phagocytosis - movement of large particles or
whole cells
2. Exocytosis
a. reverse of endocytosis
b. vesicle fuses with membrane, opens and releases
c. release proteins from Golgi apparatus