Download Methods of Cell Transport, Such As Diffusion, Osmosis, and Active

Methods of Cell Transport, Such As
Diffusion, Osmosis, and Active Transport
Plasma Membrane Is a Fluid Mosaic
• The plasma membrane is a selectively semipermeable barrier
that defines the cell and controls the passage of substances
into and out of the cell.
• Fluid Mosaic composed of Phospholipids, Proteins,
Cholesterol, Glycolipids, and Glycoproteins.
Phospholipid
Phospholipid Bilayer
Phopholipids are the main components of
membranes. They arrange themselves in a
bilayer, with their water-hating tails facing
each other, and their water-loving heads
facing the outside of the cell on one side,
and the inside of the cell on the other side.
Phospholipid Bilayer
Membrane Proteins
Roles of
membrane
proteins
include:
•Structural
•Enzyme
•Transport
•Cellrecognition
Transport Across the Membrane
Diffusion is the passing of a substance from a region
of high concentration of the substance to a region of low
concentration of the substance until equilibrium of the
substance is achieved. This is a passive process that
does not require an energy input.
Facilitated Diffusion
• Transport
Proteins
on the cell
membrane serve
as channels for
substances to
enter or exit the
cell through
passive diffusion.
Active Transport
• Active transport occurs when the cell uses ATP energy
for diffusion.
• During active transport substances may move against
their concentration gradients, that is from a region of low
concentration on one side of the membrane to a region
of high concentration on the other side.
Osmosis: Diffusion of Water
• Osmosis is the
diffusion of water,
across a
semipermeable
membrane, from a
region of high
concentration of
water to a region of
low concentration
of water, until
equilibrium of
water on both
sides of the
membrane is
reached.
Osmoregulation: Control of H2O Balance in Cells
• Tonicity: the movement of water into and out of cells in response to the
water concentration on the outside of the cell. Water moves from where it
is in high concentration to where it is in low concentration until an
equilibrium of the water concentration is reached.
Transport of Large Molecules Across the Membrane
• Endocytosis – Large
substances enter the
cell through
phagocytosis, cell
“eating” or pinocytosis,
cell “drinking”.
• Exocytosis – vesicles
fuse with the plasma
membrane and its
contents are ejected
from the cell
The Cell Is a Unit of Structure and
Function Defined by Its Membrane
• The cell’s internal environment can be very different
than that of its surroundings.
• The plasma membrane defines the area of the cell and
controls the exit and entrance of substances into and
out of the cell.