Transcript cell membrane

CELL MEMBRANE: a thin, flexible
barrier which surrounds all cells.
- regulates what enters & leaves cell
- provides protection and support.
- semi-permeable (allowing only
certain molecules (like water) to pass
freely through into or out of the cell)
Two processes to this
movement:
* Passive Transport
* Active Transport
PASSIVE TRANSPORT
Takes place without the
support of cell energy.
The most common form
of passive transport is
diffusion.
DIFFUSION: The movement
of molecules (other than
water) from a higher
concentrated area to a lower
concentrated area.
Examples: gases such as oxygen and
carbon dioxide, lipids, alcohol, some
vitamins
Importance of Diffusion to Cells and
Humans:
Cellular Respiration
Alveoli of Lungs
Capillaries
Red blood cells
Time-released medications
Rate of diffusion -depends on
temperature and size of molecules.
-molecules diffuse faster at higher
temperatures then lower
temperatures.
-- small molecules diffuse faster
than large molecules
OSMOSIS: The diffusion of
pure water (and only water) from
a higher concentrated area to a
lower concentrated area.
Cell
membrane
salt
Importance of Osmosis on Cells
and Humans:
- Cells remove water produced by
cellular respiration
- Large intestines cells transport water
to the bloodstream
- Kidney cells form urine
THE EFFECTS OF
OSMOSIS ON CELLS
HYPERTONIC SOLUTION:
the concentration of solutes is higher
outside the cell than inside – cell loses
water and shrinks.
Example: pouring salt
onto a snail/slug.
HYPOTONIC SOLUTION:
the concentration of solutes is lower
outside the cell then inside the cell – cell
gains water and swells (If the cell bursts, this is
referred to as lysis or cytolysis)
Example: Putting 100% pure
water into a patient’s IV bag
would cause excess water to get
into their cells. To keep cells
from bursting, IV’s usually
contain a salt or sugar solution.
ISOTONIC SOLUTION:
the concentration of solutes
are equal inside and outside of
the cell – cell stays the same
size
Example: Blood is isotonic to
body cells. This means that
the body cells will not shrink or
burst when they come in
contact with blood.
FACILITATED DIFFUSION:
Protein Channels assist molecules such
as glucose, amino acids, ions, etc.
across the cell membrane WITHOUT
the use of the cell’s ENERGY.
Proteins
Carbohydrate
chains
Cell
membrane
Protein
channel
Lipid bilayer
Importance of Facilitated Diffusion
to Cells and Humans:
Cells obtain food to carry out cellular
respiration
Neurons can communicate
Small intestines cells transport food to the
blood stream
Muscle cells contract
Active Transport
• Molecules move from areas of low
concentration to areas of high concentration
with the aid of ATP energy.
• Requires protein carriers called Pumps.
Importance of Active Transport
Gets rid of unwanted molecules such
as sodium from urine in the kidneys
Maintains internal conditions that are
different from the environment
Controls cellular pH levels
BULK MOVEMENT: large
molecules, like proteins, are
transported across the cell
membrane.
2 processes:
* Exocytosis
* Endocytosis
EXOCYTOSIS: wastes & cell
products such as polysaccharides,
hormones and mucous are packaged
by the Golgi Apparatus and secreted
out of the cell.
Tears
ENDOCYTOSIS: portion of the
cell membrane surrounds a desirable
molecule (such as food) outside of the
cell and takes it in (Phagocytosis &
Pinocytosis).
Phagocytosis
• “Cellular Eating” – engulfing large molecules,
whole cells, bacteria
• Ex. Macrophages ingesting bacteria or worn
out red blood cells.
• Ex. Unicellular organisms engulfing food
particles.
Pinocytosis
• “Cellular Drinking” – engulfing liquids and
small molecules dissolved in liquids;
unspecific what enters.
• Ex. Intestinal cells, Kidney cells, Plant root
cells