Transcript Cell Transport Honors Biology Mr. Lee Room 320

Homeostasis, Osmosis,
Transport
Unit 6 – Chapter 5
Diffusion Through
Cell Boundaries
 All living cells need a watery
environment to survive!
 The cell membrane helps
organisms maintain Homeostasis
(Equilibrium) by controlling what
substances enter or leave the cell
 To remain alive, cells must maintain
biological balance.
 Cells maintain this balance
(homeostasis) in response to their
immediate environment
Types of Cellular Transport
 Passive Transport
CELL DOES NOT USE ENERGY
 Diffusion
 Osmosis
 Facilitated Diffusion
Weeee!!
!
high
low
 Active Transport
CELL DOES USE ENERGY
 Protein Pumps
 Endocytosis
 Exocytosis
This is
gonna
be hard
work!!
high
low
3 Types of Passive
Transport
 Diffusion – constant motion
of molecules that causes
them to spread out from high
to low concentrations
 Osmosis – diffusion of water
 Facilitated Diffusion –
diffusion with the help of
transport proteins in the cell
membrane
Diffusion
concentration
(concentration gradient)
 Equilibrium occurs
when the
concentration of
solute (particles) is
the same throughout
(the particles still
move!)
 Because diffusion
depends upon random
particle movements
The Dye = Solute
Water= Solvent (In cells, water is always
the Solvent).
Law of Diffusion
Substances ALWAYS diffuse from
HIGH to LOW concentrations.
This fact is key to understanding
much of this chapter.
This is called moving DOWN the
Concentration Gradient.
OSMOSIS
Osmosis is the name for an important type
of diffusion. It is the diffusion of water
across the cell membrane. Since cells
are usually bathed in a watery
environment, they have to deal with water
moving in/out of them. Too much water in
or out of the cell can become a problem.
4
Osmosis – water moves from high to low
concentration
100% pure water 90% water
10% salt
level falls
level rises
membrane
More water passes from
Pure water to salt solution...
...until water
concentrations
become equal
 Water passes easily across
membranes
 Osmosis is the diffusion of
water across a selectively
permeable membrane
 Osmosis exerts a pressure
known as osmotic pressure on
the hypertonic side of a
selectively permeable
membrane
Osmosis between cells
20
If the concentration of the cell sap is greater in one cell than
in its neighbour, water will pass by osmosis from the less
concentrated to the more concentrated.
cell sap more
concentrated
cell sap less
concentrated
Osmosis in animal cells
There is a greater concentration
of free water molecules outside
the cell than inside
so water diffuses into the cell
by osmosis
and the cell swells up
Plant cells
cell wall
vacuole
The cell absorbs water
by osmosis ....
cytoplasm and
cell membrane
....but the cell wall stops the
cell expanding any more
Solutions
The relative concentrations of solutions to one
another inside/outside of the cell can lead to 3
different situations. These situations are
known as:
1. Isotonic
2. Hypertonic
3. Hypotonic
** The next few slides will illustrate how these
situations affect the cell.
Isotonic
Hypertonic
 Solute concentration is
greater outside the cell,
so water moves OUT of
the cell
 Remember, hypertonic,
the cell shrinks
 The shrinking of cells is
called Plasmolysis
Hypotonic
 Solution
concentration is
greater inside the
cell, so water moves
INTO the cell
 Remember,
hypotonic, the cell
POPS!!!
• The bursting of cells
is called Cytolysis
How Single Celled Critters
Deal with Osmosis
 Unicellular organisms in
hypotonic environments
need to get rid of the
excess water that
diffuses into them
 Contractile vacuoles are
organelles that collect
water and pump it out of
the cell (uses energy)
How Multi-celled Critters
Deal with Osmosis
 Other cells (especially in multicellular
organisms) respond to a hypotonic
environment by pumping solutes
out of the cytoplasm
 Water molecules are less likely
to diffuse into the cell
Types of Passive Transport
(How cells transport materials in/out of
themselves) – NO CELL ENERGY REQUIRED
1. Osmosis
2. Facilitated Diffusion
3. Ion Channels
**Refer to the next 2 slides.
Facilitated Diffusion
 Some molecules cannot diffuse
through the cell membrane
because they are:
 Not soluble in lipids
 Or are too large to pass through
the pores in the membrane (I.E.
Glucose)
 These molecules are helped
across the membrane by carrier
proteins
 The carrier proteins change
Diffusion Through
Ion Channels
 Ions such as sodium (Na+),
potassium (K+), calcium (Ca2+),
and chloride (Cl-) are important
for cell functions
 Since they are not soluble in
lipids they will not pass through
the cell membrane on their own
Diffusion Through
Ion Channels…
 Ion channels provide small tunnels
across the cell membrane
 Each type of ion channel is usually
specific for one type of ion
 Some channels are always open, some
are gated
 The gates respond to three stimuli:
 Stretching of the cell membrane
 Electrical signals
 Chemicals in the cytosol or external
environment
Active Transport – (cells actively work to
move some substances in/out) – CELL
ENERGY IS REQUIRED
1. Pumps in the cell membrane – proteins in the cell
membrane use cell energy to change their shape to
actively pump molecules in/out of cell. Ex.)
Sodium/Potassium Pump.
2. Endocytosis – moving very large molecules INTO the
cell. Cell wraps its membrane around the large
molecule. This requires the cell to spend energy.
3. Exocytosis – moving large OUT OF the cell. Cell
membrane changes its shape to push molecule out of
cell. This requires cell energy.
***See pages 101 to 104 in book.