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Cellular Transport
Review of Diffusion
• Movement of particles
from an area of higher
concentration to an
area of lower
concentration.
Osmosis
• Diffusion of water across a selectively
permeable membrane.
• Controlled by concentration gradients.
– Regulation of osmosis by the cell maintains
homeostasis.
Cells in Isotonic Solutions
• Concentration of both dissolved substances and
water in the solution is the same as the
concentration of dissolved substances and water
in the cell.
• Osmosis occurs with water diffusing in and out
of the cell at the same rate.
• Cell retains its original shape.
Cells in Isotonic Solutions
Cells in Hypotonic Solutions
• Concentration of dissolved substances is
lower in the solution outside the cell than
the concentration of dissolved substances
inside the cell.
• More water outside the cell than inside the
cell.
• Water moves through the plasma
membrane into the cell.
• Cell swells and the internal pressure
increases.
Cells in Hypotonic Solutions
•http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm
Cells in Hypotonic Solutions
• If the solution is extremely hypotonic,
pressure may be so great that animal cells
may burst.
• Plant cells will not usually burst because
they contain a rigid cell wall against which
the plasma membrane is pressed, causing
the cell to become more firm.
Cells in Hypertonic Solutions
• Concentration of dissolved substances outside
the cell is higher than the concentration of
dissolved substances inside the cell.
• Water is greater inside the cell and flows out of
the cell across the plasma membrane.
Cells in Hypertonic Solutions
http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm
Cells in Hypertonic Solutions
• Animal cells will shrivel because of the
decreased pressure.
• The cell wall maintains the shape of plant
cells, but the plasma membrane pulls
away from the cell wall, causing the plant
to wilt.
Passive Transport
• Movement of particles across the
membrane in which the cell does not need
to use energy to move particles.
• 2 Main Types:
– Simple Diffusion
– Facilitated Diffusion
Simple Diffusion
Facilitated Diffusion
• Passive transport of materials across the
membrane using transport proteins.
• Two types of transport proteins:
– Channel Proteins
– Carrier Proteins
Channel Proteins
• Type of transport protein.
• Form channels that allow
specific molecules to flow
through.
• Movement of material is with the
concentration gradient.
• No energy input by the cell is
required.
Carrier Proteins
• Change shape to allow a substance to pass
through the plasma membrane.
Active Transport
• Movement of particles from a region of
lower concentration to an area of higher
concentration (against the concentration
gradient.
• Cell must expend energy to counteract the
force of diffusion moving particles in
opposite direction.
Steps in Active Transport
1. Carrier protein bonds with the substance
to be transported.
•
In general, each type of carrier protein has a
shape that fits a specific molecule or ion.
2. When the proper molecule bonds with
the protein, chemical energy allows the
cell to change the shape of the carrier
protein.
Steps in Active Transport
3. The substance to be moved is released
on the other side of the protein.
4. The original shape of the protein is
restored.
Active Transport
Endocytosis
• Process by which a cell surrounds and
takes in material from its environment.
• The material doesn’t pass through the
membrane but is engulfed by a portion of
the plasma membrane.
• The portion of the plasma membrane then
breaks away and the resulting vacuole,
along with its contents, moves to the
inside of the cell.
Endocytosis
Exocytosis
• Expulsion or secretion of materials from a cell.
• Used to expel wastes and to secrete substances
such as hormones produced by the cell.