Transcript The Cell Membrane

• Functions:
– Structural support & protection
– Helps maintain HOMEOSTASIS
– Selective barrier –SEMIPERMEABLE
• Water, food, oxygen, waste and nutrients are
transported through the cell membrane.
Structure
• Lipid Bilayer = Double
layer of phospholipids
• Each Phospholipid has:
– 2 non-polar tails:
Hydrophobic (Repels
water, Water FEARING)
– 1 polar head: Hydrophilic
(Attracted to water,
Water LOVING)
• Proteins, carbohydrates,
and cholesterol are also
in the membrane
Homeostasis
• The maintenance of stable internal conditions
within the cell or organism.
• The body’s ability to maintain equilibrium
BALANCE
• Conditions within and around organisms are
constantly changing (temperature, water, oxygen), so
our cells need a way to adjust to the changing
conditions.
Semipermeable
• Some substances can pass across it and others can not
• Also called “Selectively Permeable”
• Large molecules such as proteins and sugars don’t pass
freely and must be transported into the cell
Passive Transport
Allows some particles to move in or out of cell
without the use of energy.
•Using Diffusion
Diffusion-
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/ani
mation__how_diffusion_works.html
– particles spread from high concentration to low
concentration until equilibrium is reached
– movement of Solutes (sugar, salt, minerals)
– No energy required
Concentration Gradient- difference in
concentration between two areas across
from each other.
Molecules will move with the gradient
from a high concentration to a lower
concentration .
“Rolling down a hill doesn’t require
energy”
Solutions
• Solute is the material that is being dissolved (sugar)
• Solvent is doing the dissolving (water)
Types of Diffusion
• Simple—unassisted diffusion of
small particles or lipid-soluble
molecules
• Osmosis—unassisted diffusion of
water
• Facilitated diffusion—diffusion
with the help of carrier proteins
• Osmosis:
– diffusion of water from an area of high to low water
concentration
– Occurs continuously (all the time) in the cell
– No energy required
•HYPERTONIC solution:
1. Solute concentration outside the cell is higher (less water)
2. Water diffuses out of the cell
3. Cell will shrink
Plant cell-cell membrane pulls
away from the cell wall (wilts)
•HYPOTONIC solution:
1. Solute concentration greater inside the cell (less water)
2. Water moves into the cell
3. Cell will swell & burst (Lysis)
Plant cell-pressure on cell
wall increases- (Turgor)
•ISOTONIC solution:
1.Concentration of solutes is the same
inside & outside the cell
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2
/animation__how_osmosis_works.html
• Facilitated Diffusion
– transport proteins embedded in cell membrane
“carries” the substance across the membrane.
– Substances like glucose, amino acids, and ions use
these
– No energy required
http://highered.mcgrawhill.com/sites/0072495855/stu
dent_view0/chapter2/animati
on__how_facilitated_diffusion
_works.html
Cell in Isotonic Solution
10% NaCL
90% H2O
ENVIRONMENT
CELL
10% NaCL
90% H2O
NO NET
MOVEMENT
What is the direction of water movement?
The cell is at __________.
Equilibrium
Cell in Hypotonic Solution
10% NaCL
90% H2O
CELL
20% NaCL
80% H2O
(More H20 outside of cell than inside)
What is the direction of water movement?
Cell in Hypertonic Solution
15% NaCl
85% H2O
ENVIRONMENT
CELL
5% NaCl
95% H2O
(More H20 inside than outside)
What is the direction of water movement?
Active Transport
• Movement of substances from a lower
concentration to a higher concentration
• Energy is needed
– ATP (adenosine triphosphate) is the source of the energy.
• Transport goes AGAINST concentration gradient
(going up a hill requires energy)
• Carrier Proteins (Transport Proteins)
– Endocytosis
– Exocytosis
• Carrier Proteins (Transport Proteins)
– Use ATP to pump molecules into or out of the cell
– Low concentration to high concentration
• Endocytosis
– Cell membrane folds inward surrounding the material
to transport it INTO the cell
– Once inside the cell it’s transported to a lysosome
Two Types of Endocytosis
Phagocytosis
• “Cell Eating”
• Engulfs large materials like
bacteria
Pinocytosis
• “Cell Drinking”
• Engulfs extracellular fluid,
including sugar and proteins
• Exocytosis
– Materials, like waste, are surrounded by a vesicle and
transported to the cell membrane
– Vesicle fuses with the cell membrane and releases its
contents OUTSIDE the cell