Download Phospholipids make up cell membranes

Warm-Up
organelles
11/8/11
Why would plants need to have both
chloroplasts and mitochondria? (Look at
function for each)
Have out animal and plant drawings to be
stamped
Cell Membranes vs. Cell Walls
 Cell Membranes
regulate what
comes into and
out of cells
 Cell Walls
provide
protection and
support for
the cell
Phospholipids make up
cell membranes
Polar “head” that is
attracted to water
Non-polar “tails” that are
not attracted to water but
are attracted to other
phospholipid tails
Phospholipids make up cell
membranes
Water molecules
Polar head faces
out towards water
because of the
attraction
Nonpolar tails face
inward so they are
protected from water
Water
Electron micrograph of
cell membrane
Inside cell
layer
Outside cell
layer
Membranes are picky!!!
 Membranes are semi-permeable because
they only let certain molecules through
 Small and non-polar molecules can pass
through easily (water, oxygen, carbon
dioxide)
 Large and polar molecules cannot pass
through without help (starch, glucose,
proteins, amino acids, ions)
Diffusion and Osmosis
Diffusion- The movement of particles from
a region of higher concentration to a
region of lower concentration, caused by
the random motion of particles.
Osmosis- The diffusion of water across a
semi-permeable membrane towards the
side with higher solute concentration.
Why does osmosis happen?
Two factors cause osmosis:
1. A semipermeable membrane allows water
molecules to move back and forth through
the membrane, but not solute molecules
2. Water molecules “stick” temporarily to any
dissolved solute molecules.
As a result, water molecules spend more time
and accumulate on the side of the membrane
with the higher concentration of dissolved
solutes.
Solutions
 Solute- the substance dissolved in a
solution
 Solvent- the substance in which a solute
is dissolved
 Example
In a solution of salt dissolved in water:
Salt is the solute; water is the solvent
Types of Solutions
 hypertonic solution- a solution with a higher
solute concentration than what it is compared
with.
 hypotonic solution- a solution with a lower
solute concentration than what it is compared
with.
 isotonic solution a solution with an equal
solute concentration to what it is compared
with.
Visual Examples
Solution is hypotonic to cell.
Cell is hypertonic to solution.
Solution is hypertonic to cell.
Cell is hypotonic to solution.
Solution is isotonic to cell.
Cell is isotonic to solution.
Facilitated diffusion
The movement of molecules across a cell
membrane from an area of higher
concentration to an area of lower
concentration with the help of a carrier
protein. This transport does NOT require
energy to happen. Moving large
molecules.
Passive transport
Passive transport happens spontaneously across
the cell membrane. It does NOT require any
cellular energy (ATP) because molecules
move DOWN their concentration gradients
(from high to low concentration).
There are two types of passive diffusion:
1. Simple diffusion: molecules pass directly
through the lipid bilayer.
2. Facilitated diffusion: molecules are too big to
pass through the lipid bilayer. They bind to a
carrier protein to diffuse across the
membrane.
Passive transport
Simple diffusion
Facilitated diffusion
Concentration Gradient
Carrier protein
3 steps in facilitated
diffusion
1. Particle binds to
one side of carrier
protein
2. Carrier protein
changes shape
3. Particle diffuses
to other side of
membrane
Active transport
The movement of molecules across a cell
membrane from an area of low
concentration to an area of higher
concentration (“up” or “against” the
concentration gradient). Active transport
requires the use of energy (ATP).
Starch/Iodine Lab- Lab set up due
Wednesday
• How does the size of molecules affect their
diffusion across a semi-permeable membrane?
• Create two experimental procedures to
demonstrate question (pictures or words)
– Must keep solutions separate
– Iodine solution (water with 10 drops of iodine)
– Hypothesis is your prediction on what will happen
• Which molecule will move
• Where will the color change take place
Homework:
 Section 7.3 assessment questions, due
Wednesday