Moving Substances Across Cell
Membrane
• cell membrane is semi–permeable
• Some molecules pass through easily, some need help
• Some molecules pass through without the expenditure of
energy (spontaneous) and some require an input of energy
(ATP)
What molecules move IN and OUT of a cell:
•
•
•
•
•
Small nonpolar molecules (CO2, O2)
Small polar molecules such as water
Ions and charged molecules
Large polar molecules (eg. Glucose)
Macromolecules
Movement IN
and OUT can
Be PASSIVE or
ACTIVE
Passive Transport
•
•
•
cell uses no energy
molecules move randomly
Molecules spread out from an area of high
concentration to an area of low
concentration.
Weeee!!!
[High][Low]
Three types:
1. Diffusion
2. Facilitative Diffusion
3. Osmosis
high
low
Passive Transport:
Simple Diffusion
Animation
1. Diffusion: random movement of
particles from an area of [high]
to an area of [low].
•
diffusion continues until all
molecules are evenly spaced
(equilibrium is reached)Note: molecules will still move
around but stay spread out.
http://bio.winona.edu/berg/Free.htm
Passive Transport:
2. Facilitated diffusion:
A
B
Facilitated
diffusion
(Channel
Protein)
Diffusion
(Lipid
Bilayer)
diffusion of particles from
[H  L] through transport
proteins found in the
membrane
Transport Proteins are
specific – they “select” only
certain molecules to cross
the membrane
Carrier Protein
Passive Transport:
diffusion of
water through a
selectively
permeable
membrane from an
area of [H  L]
Osmosis
animation
3.Osmosis:
•Water moves freely
through pores.
•Solute (green) too large
to move across.
Effects of Osmosis on Life
• Water molecules are so small and so numerous that cells can’t
control movement of water through the cell membrane.
So what determines the direction of water movement?
The environment around the cell,
…specifically,
the concentration of water molecules inside the cell
compared to outside
Environment around the cell is either:
HYPOTONIC, ISOTONIC, HYPERTONIC
But first - Don’t confuse Volume of
water with Concentration
Equal Volumes, Different
Concentration
•
Hypotonic Solution
Osmosis Animations
for isotonic,
hypertonic, and
hypotonic solutions
Hypotonic: The external environment (ECF) has a lower
concentration of solutes and a higher concentration of
water than inside the cell.
Result: Water moves from the ECF to inside the cell
- Cell Swells and bursts open (cytolysis)!
Compare a blood
cell in an isotonic
environment with
one in a hypotonic
environment
•
Isotonic Solution
Osmosis Animations
for isotonic,
hypertonic, and
hypotonic solutions
Isotonic: The concentration of solutes in the ECF is equal
to the concentration of solutes inside the cell.
Result: Water moves equally in both directions and the
cell remains same size. (Dynamic Equilibrium)
Water on the way out
•
Hypertonic Solution
Osmosis Animations
for isotonic,
hypertonic, and
hypotonic solutions
Hypertonic: The ECF has a higher concentration of solutes
and a lower concentration of water than inside the cell.
shrinks
Result: Water moves from inside the cell into the solution:
Cell shrinks. Plasmolysis (plant cell) Crenation (animal cell)
In what type of solution are these cells?
A
B
C
Plant cells
resist
bursting.
Why?
Hypertonic
Isotonic
Hypotonic
•Animations of Active
Transport & Passive
Transport
Active Transport
•cell uses energy
•actively moves molecules to where they are needed
•Movement of molecules from an area of [low] to
an area of [high]
Three Types
1. Protein Pumps
2. Endocytosis
3. Exocytosis
This is
gonna be
hard
work!!
high
low
Types of Active Transport
1. Protein Pumps –are
special transport proteins
that help move molecules
IN/OUT - require energy to
do work
example: Na+/K+
Potassium Pumps are
important in nerve
responses.
Sodium Potassium
Pumps (Active
Transport using
proteins)
Protein changes shape
to move molecules:
this requires energy!
Types of Active Transport
• 2. Endocytosis: taking bulky
material into a cell
• Uses energy
• Cell membrane folds itself
around food particle
• “cell eating”
• forms food vacuole &
digests food
• This is how white blood
cells eat bacteria!
Types of Active Transport
3. Exocytosis: Forces material
out of cell in bulk
• membrane surrounding
the material fuses with cell
membrane
• Cell changes shape –
requires energy
• EX: Hormones or wastes
released from cell
Endocytosis &
Exocytosis
animations
• Endocytosis_[www.k
eepvid.com].mp4
• Active_Transport_~~
_[www.keepvid.com]
.mp4