Download Passive Transport - Liberty Union High School District

Homeostasis
and
Membrane Transport
Part 1
Chapter 3
The big picture!
 Living
things strive for balance or
homeostasis

Homeostasis: Stable internal conditions
of a living thing; balance.
Equilibrium: Everything is in
perfect balance.
 Transport
across a membrane is one
way the body achieves balance.
 Cell

membrane is semi-permeable
Semi-permeable: only certain things can
enter or exit the cell
Close-up view of the
cell membrane
 Cell
Membrane is made of 2 main parts…
 1) Phospholipid bilayer (2 layers of
special lipids)
Hydrophilic
“heads” are
attracted to
water
Hydrophobic
“tails” repel
water and point
away from it
Video clip of membrane (1:27):
http://www.youtube.com/watch?v=Qqsf_UJcfB
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Pair Share #1
 Define
homeostasis in your
own words.
 What are some things your
body tries to keep balanced?
Our bodies must balance various
solutions
 Solution:
a mixture of things
dissolved in water.
 Ex: Blood is a solution of cells,
nutrients, oxygen, carbon dioxide,
waste products, and other
molecules floating in water
 Concentration:
is a measure of how
much substance there is compared to
how much water
 Solute: substance being dissolved,
like sugar or salt
 Solvent: substance doing the
dissolving
(water)
LOW
CONCENTRATION
Less Solute
More Solvent (water)
HIGH
CONCENTRATION
More Solute
Less Solvent (water)
Pair Share #2
 Which
solution is more
concentrated:
3% salt solution or 5% salt
solution?
 Concentration
Gradient: when
there is a difference of
concentrations between two
sides.
Not a concentration
gradient (equal on
both sides)
Concentration
gradient
There are 3 Solution Types:
1. Isotonic: Two solutions have the
same concentration
2. Hypotonic: A LESS concentrated
solution
• Water > solute
3. Hypertonic: A MORE concentrated
solution
• Water < solute
When a cell is in an isotonic
solution…
•Water and solutes move both
ways equally.
When a cell is in a hypertonic
solution…
•Solution is more concentrated than cell
•Water leaves the cell and goes into the
solution
•Cell shrinks, shrivels
When a cell is in a
hypotonic
solution…
•Solution is less
concentrated than cell
• Water from solution
will go into the cell
• Cell swells and can
burst (“lyse”) unless it
has a cell wall to
prevent this
ISOTONIC
SOLUTION
ANIMAL
CELL
PLANT
CELL
HYPOTONIC
SOLUTION
HYPERTONIC
SOLUTION
 Passive
Transport: No energy
(ATP) is needed. Moves WITH
the concentration gradient
 (high
3
 low)
Types of Passive Transport:
1. Diffusion
2. Osmosis
3. Facilitated Diffusion
1. Diffusion: movement of molecules
(other than water) from an area of higher
concentration to an area of lower
concentration
 Diffusion will continue until an
equilibrium is reached.
Osmosis
2. Osmosis: Osmosis is the
diffusion of water
 Water moves from where there is
more water molecules to less
water molecules.
Pair Share #3
 True
or false?
 Osmosis
is the diffusion of starch
molecules through a selectively
permeable membrane.
3. Facilitated Diffusion: When
molecules cannot squeeze through
phospholipids, they use
channel/carrier proteins to enter/exit
the cell