Download Cell Membrane Notes

THE CELL AND ITS
ENVIRONMENT
HOMEOSTASIS
 Homeostasis
“ steady state” or balance
cells constantly seek homeostasis
 The
Cell Membrane is responsible for
maintaining the steady state within cells.
Most cells live in some kind of fluid
 Single celled organisms – ponds, oceans,
other bodies!?!
 Multicellular organism cells are surrounded
by body fluid

HOMEOSTASIS CONTINUED:
Cells
have limits to the changes
they can survive:
 Temperature
 Salt concentrations in water
 Interstitial fluid – body fluid
between cells
DIFFUSION
 Molecules
move from a area of high
concentration to an area of low
concentration
Takes place in both solutions and air
 Gradual spreading out of the molecules
 The spread out until the reach
equilibrium

 REQUIRES
NO ENERGY!
DIFFUSION THROUGH MEMBRANES
 Permeable

when membranes allow all substances to pass
through
 Selectively

Permeable
when membranes allow some substances to
pass through, & others not
CELL MEMBRANES ARE SELECTIVELY
PERMEABLE!
Osmosis-
 diffusion
of water through a
selectively permeable membrane
Remember
from high
concentrations to low
concentrations or…
“HIGH to LOW”
Q?:
What decides what moves into the cell???
A:
Compare the solution outside the cell to the
solution inside the cell.
Hypotonic- a solution having a lower concentration
of solutes than the cell

Hypertonic- a solution having a higher
concentration of solutes than the cell

Isotonic- a solution having the same concentration
of solutes as the cell

RULES FOR DECIDING WHAT WILL HAPPEN
TO CELLS…
look at the solute concentrations to set up the
picture puzzle
2.
water moves first and fastest….so
3.
look at the water concentrations to decide what
will happen to the cell…try some problems
…OR
“Water Follows Solute”
1.
TURGOR PRESSURE term
used to describe water pressure within
a cell, (usually plant cells)
 will continue to build up until equilibrium is
reached
 Even if that means EXPLODING! This
doesn’t happen often – plant cells are
protected by their cell wall
PLASMOLYSIS
water diffuses out of a cell and turgor pressure is
lost
 plants “wilt”
 cells shrink

CYTOLYSIS
when cells burst because water pressure inside the
cell is too great
 This is why sea animals can not live in fresh water
(lakes).
 They are not built to pump out the extra water

2 WAYS SUBSTANCES ARE
TRANSPORTED THROUGH
MEMBRANES
PASSIVE TRANSPORT- the movement of
substances through the cell membrane when NO
ENERGY taken from the cell

Osmosis
Diffusion
 Facilitated Diffusion 




Has the help of a protein channel
These both happen “naturally”
SUBSTANCES THAT USE PASSIVE
TRANSPORT
Water
 Carbon Dioxide
 Oxygen
 Steroids
 Alcohol
 Glucose

ACTIVE TRANSPORT
Transporting substances across
membranes USING ENERGY from the
cell
 Examples:

Sodium (Na+)
 Potassium (K+)

The cells have high needs of these ions
 Active Transport moves against natural
diffusion


Plants have the ability to absorb Na and K
when concentrations are higher inside the
cell than outside the cell
ACTIVE TRANSPORT (CONT.)
Endocytosis- taking into a cell
 Exocytosis- putting out of a cell
 Phagocytosis- taking in large solid
 Pinocytosis- taking in or putting out fluid drops



excrete or secrete (like sweat!)
Cells reach around the particle to be taken in and form a
pouch!
REVIEW QUESTIONS!
Describe the functions of the cell membrane and
cell wall.
 What happens during diffusion?
 Describe how water moves during osmosis.
 What is the basic structure of a cell membrane?
 What is the difference between phagocytosis and
pinocytosis?
 Critical Thinking Comparing and Contrasting
What is the main way that active transport
differs from diffusion?
