Download HOMEOSTASIS AND THE CELL MEMBRANE

HOMEOSTASIS AND THE CELL MEMBRANE
HOMEOSTASIS – MAINTAINING CONSTANT INTERNAL CONDITIONS
I. Transportation through the Cell Membrane— small molecules such as H2O, CO2 and O2 move easily through the lipid
bilayer – larger molecules require different mechanism
A. Passive transport – NO energy required
1. Diffusion -- movement of particles from a high concentration to a low concentration
a. example: dye (ex: food coloring) in water
dye diffuses down
concentration gradient
until equilibrium reached
concentration gradient =
difference in
concentration of a
substance
b. example: blood vessel in lung tissue during respiration
blood
X
X
X
X
X
X
CO2
high
l lung
l
l O O
l O O
l O O
l
blood
X O
O X
X O
O2
high
c. example: sugar dissolved in water
solution – sugar water
solvent – water (dissolving substance)
solute – sugar (substance being dissolved)
l
l
l
l
l
l
lung
X O
O X
X O
solute
(sugar cube)
solution
solvent (H2O)
2. Osmosis -- diffusion of water through a selectively permeable membrane
permeable to H2O
impermeable to salt
Water
Salt
salt water
tap water
Hypotonic =
Low Salt Concentration
High Water Concentration
High Salt Concentration
Low Water Concentration
= Hypertonic
a. hypertonic solution – high in solutes, low in solvent
hypotonic solution – low in solutes, high in solvent
isotonic solution – equilibrium has been reached
Ex: cell in salt water
water
moves
into cell
water
moves in
and out of
cell
water
moves
out of cell
cytolysis
plasmolysis
Red Blood Cell
SALT SUCKS!!
Plant cell
b. example problem: A cell that is 80% H2O and 20% other is put into water that is 99% H2O and 1% other.
Which way will the water move? Into cell
99% H2O
Which is the hypotonic solution? Outside cell
1% other
Which is the hypertonic solution? Inside cell
c. cell bursts – cytolysis
cell shrinks – plasmolysis (lysis = splitting)
80% H2O
20% other
3. Facilitated diffusion-- Most molecules move across the membrane with help from protein channels - provides a
larger opening for organic molecules to go through
a. example: glucose (food molecules)
Glucose molecules (high concentration)
outside of cell
protein
protein
pump
channel
--------------------------------------------------------------NO ENERGY REQUIRED------------------------------------------------------------------inside of cell
-----------------------------------------------------------------ENERGY REQUIRED-------------------------------------------------------------------B. Active transport – energy required in form of ATP
1. Some proteins act like pumps moving molecules from LOW to HIGH concentration.
a. example: vitamins and minerals in soil concentrated into plants
= calcium ion
Outside cell
Inside cell
b. example: Body cells must pump CO2 out into the surrounding blood vessels to be carried to the lungs to exhale.
Blood vessels are high in CO2 compared to the cells, so energy is required to move the CO2 across the
cell membrane from LOW to HIGH concentration.
outside of cell
inside of cell
Carbon dioxide
molecules
Protein pump
2. Endocytosis/ Exocytosis – how very large molecules (food and waste) get into and out of cell
a. Endocytosis – into cell
1. Phagocytosis – solids
example: white blood cell engulfing bacteria to destroy it (immune reaction)
2. Pinocytosis – liquids
example: water into cell
b. Exocytosis – out of cell
example: cellular waste
II. Flow Chart
A. Homeostasis – maintaining constant internal conditions
B. Cell membrane constantly working on maintaining homeostasis within the cell
NO ENERGY NEEDED: high to low conc.
Passive Transport
Diffusion
Osmosis
Facilitated Diffusion (protein channels)
ENERGY NEEDED: low to high conc.
Active Transport
Endocytosis (phagocytosis
and pinocytosis)
Exocytosis
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