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BELL WORK:
Answer the following questions on
your bell work page:
1. A scientist finds a unicellular organism. He can
see its DNA is free-floating in the center of the
cell. What kind of cell is this, and how do you
know?
2. Which organelles help produce and move
proteins in a cell? (hint: there are THREE)
Today’s Standard (B.4B): Investigate
and explain cellular processes
including…transport of molecules
Today’s Essential Question: How do
molecules move in a cell?
CELL MEMBRANE: a thin, flexible barrier
surrounding all cells
What is the cell membrane’s
function (job)?
(2 things)
Two main functions:
1) regulate what enters (food, water, &
oxygen) & leaves (waste)
2) provide protection & support
What is the cell membrane
composed (made) of?
(3 types of molecules)
LIPIDS: the main component of a cell
membrane
–Found in a double layer called the lipid
bilayer
–Also called the phospholipid bilayer
–hydrophobic (afraid of water)
DRAW
THIS!
PROTEINS: embedded into the lipid
bilayer
–Form channels or pumps (pathways)
to help move large molecules
CARBOHYDRATES: attached to many
proteins on the outside of the bilayer
– allow cells to communicate with each
other
carbohydrates
How do molecules move in or out
through the cell membrane?
Why does food coloring spread out in water?
• In a solution,
particles are
constantly moving.
• They collide with
one another and
spread out
randomly.
DIFFUSION: particles move from an
area of HIGH concentration to an area
of LOW concentration
CONCENTRATION: the amount of solute
(stuff) dissolved into a solvent (liquid)
KOOL-AID is the solute
WATER is the solvent
CONCENTRATION is
how much Kool-Aid
you put in
CONCENTRATION GRADIENT: a
difference between two concentrations
If diffusion is going from
high concentration to
low concentration, what
direction is it moving on
the concentration
gradient?
High
Concentration
Low Concentration
EQUILIBRIUM: the concentration of a
solute is the same throughout a system
–particles continue to move
–the goal of diffusion!
Diffusion
does NOT
require
energy!!
The rate (speed) at which molecules
pass through a membrane depends
on its permeability.
PERMEABLE membranes
allow all substances to
pass through
IMPERMEABLE
membranes allow no
substances to pass
through
Biological (cell) membranes are
SELECTIVELY permeable
–Some substances can pass through, while
others cannot
OSMOSIS: diffusion of water through
a selectively permeable membrane
–does NOT require energy!