Download The Cell Membrane

The Cell Membrane
Cell Transport
The Cell(Plasma) Membrane
• A thin flexible layer that surrounds all cells and
regulates what enters and leaves the cytoplasm
of the cell.
Parts of the Cell Membrane
• The cell membrane is
made primarily of
phospholipids.
• Phospholipids have a
hydrophilic,
phosphate head and
2 hydrophobic fatty
acid tails.
• Water molecules
surround the
membrane.
• The result is a double
layer called a
phospholipid bilayer.
Parts of the Cell Membrane
• Cholesterol is needed
in animal cell
membranes to prevent
the body from freezing
at low temperatures. It
also makes the
membrane more firm.
• The arrangement of
phospholipids in the
bilayer makes the cell
membrane selectively
permeable.
Fluid Mosaic Model
Parts of the Cell Membrane
• Integral Proteins-exposed to the interior
and exterior of the membrane. They
detect environmental signals and transmit
them to the inside of the cell. Usually has
carbohydrates attached.
– These carbohydrates acts as labels on the
surface. Some labels help cells recognize
each other and stick together.
– Unfortunately, viruses can use these labels as
docks for entering and infecting cells.
Parts of the Cell Membrane
• Peripheral Proteins-not embedded in the
membrane.
• Transport Proteins- helps substances
move across cell membrane.
Fluid Mosaic Model
• Scientists describe the cell membrane as
a fluid mosaic.
– The fluid mosaic states that the phospholipid
bilayer behaves like a fluid more than a solid.
What needs to move into and out of
the cell?
• Oxygen, Water, Nutrients need to enter
the cell.
• Carbon Dioxide, other wastes, and
proteins need to leave the cell.
• Where would you rather be traveling on the road?
• We would want to get away from the high
concentration of cars, to a more open or less
concentrated road.
Types of Cell Transport
• Diffusion- Particles move from an area of
high to low concentration without using
any of the cell’s energy
» A type of passive transport (No energy required)
» Diffusion will eventually cause the molecules to be in
equilibrium.
» Even after equilibrium is reached, the movement of
molecules continue to move.
Diffusion
Osmosis
• The process by which water molecules
diffuse across a membrane from an area
of high concentration to low concentration.
– Energy is not needed for osmosis to
occur. (Passive Transport)
– http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_os
mosis_works.html
• Concentration Gradient- the difference in
the concentration from one point to
another.
What happens to a cell in different
situations?
• Plasmolysis -the shrinking or contraction
of a cell.
– What type of solution would the cell be in for
this to occur?
• Cytolysis- the bursting of cells.
– What type of solution would this cell be in for
this to occur?
Finding Nemo
• Saltwater Fish vs. Freshwater Fish
• Why do you think that some fish cannot
survive in freshwater?
Facilitated Diffusion-(passive)
• A protein channel in the cell membrane
helps a molecule into or out of the cell.
•
•
Facilitated Diffusion 2
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.ht
ml
Active Transport
• Particles move from LOW to HIGH
concentration (against the concentration
gradient) with the use of ENERGY (ATP).
•
Active Transport
Types of Active Transport
• Endocytosis – Particles enter the cell
– Pinocytosis-the transport of solutes or fluids
– Phagocytosis-the movement of large particles
or whole cells.(food)
• Exocytosis – Particles are released or
exits the cell
The membrane is Semi-Permeable
(Only some things can enter the cell)
• Small polar and non-polar molecules can enter
through the cell membrane.
– Water, Oxygen, Carbon Dioxide
• Large polar molecules cannot make it through
the “water hating” areas. They need help to
enter the cell.
– ions
• Large non-polar molecules also need help to
enter the cell.
– Glucose
Semi-Permeable Animation
Where salt goes, water flows!
• If there is a higher concentration of salt in
one area, water will flow toward the higher
salt concentration. (Toward the area
where there is less water).
• Why do you feel
thirsty when you
eat french fries?