Download 8.2 Cell Transport

Key Ideas
• What determines the direction in which
passive transport occurs?
• Why is osmosis important?
• How do substances move against their
concentration gradients?
8-2 Cell Transport
Cell Transport
•
Must move substances of varying size, electrical
charge, and composition into and out of the cell
2 types of transport
1. Passive
–
–
Does not use energy
Moves from a high concentration to a low
concentration
2. Active
–
–
Requires energy
Moves from a low concentration to a high
concentration
Passive Transport- Terms
• Equilibrium
– Results when the concentration of a substance is the
same through out a space
• Concentration
– The amount of a particular substance in a given
volume
• Concentration gradient
– Occurs when one area has a higher concentration
than another area does.
Passive Transport-Simple Diffusion
Diffusion
• The movement of particles from regions
of higher density to regions of lower
density across the cell membrane.
• The direction of movement depends on
the concentration gradient and does not
require energy.
Passive Transport-Simple Diffusion
Diffusion
Facilitated
Diffusion
Passive Transport
Facilitated Diffusion
• Transport proteins
– Helps ions and polar molecules diffuse through
the membrane
2 types
• Channel proteins or pores
• Carrier proteins
Passive Transport
Facilitated Diffusion
• Channel proteins or pores
– Act as a tunnel through the membrane
– Allow specific ions, sugars, and polar
molecules to pass
• Carrier
– Transports substances that fit within their
binding site
– Results in changing the shape of the protein
and the delivery of the substance to the other
side of the cell
Passive Transport
Facilitated Diffusion
Passive Transport: Osmosis
Osmosis
• the diffusion of water across a selectively
permeable membrane
• Allows cells to maintain balance as their
environment changes.
Passive Transport: Osmosis
Passive Transport: Osmosis
Water Channels
• form of facilitated diffusion
• Polar water molecules must rely on channel
proteins in the cell membrane that only allow
water molecules to pass through.
Passive Transport: Osmosis
Predicting Water Movement
• Hypertonic
– Water moves out
• Hypotonic
– Water moves in
• Isotonic
– Water diffuses in and out of the cell at an equal rate
Effects of Osmosis
• If left unchecked, the swelling caused by a hypotonic solution
could cause a cell to burst.
Ways to prevent the cell from bursting
• rigid cell walls of plants and fungi prevent the cells from
expanding too much.
– many plants are healthiest in a hypotonic environment.
• Some unicellular eukaryotes have contractile vacuoles
– which collect excess water inside the cell and force the water out of the
cell.
• Animal cells have neither cell walls nor contractile vacuoles.
– avoid swelling caused by osmosis by actively removing solutes from
the cytoplasm.
Active Transport
Review
• Requires energy
• Moves against the concentration
gradient – move from low concentration
to high concentration
Active Transport
Pumps
• Requires carrier proteins
• Ex. sodium-potassium pump
– sodium ions bind to the carrier protein
– through the use of energy(ATP) changes shape
releasing sodium to the outside of the membrane
– while open to the outside, potassium ions bind to the
carrier protein
– when the pump returns to its original shape the
potassium ions are released on the inside.
– For every 3 sodium ions taken out there are 2 potassium
ions taken in
Active Transport
Vesicles
• Allows proteins, polysaccharides, and other
substances that are too large to be transported by
carrier proteins
• Contain the same lipid bilayer as the membrane
so vesicles can easily break off and fuse with the
membrane
2 types
• Exocytosis
• Endocytosis
Endocytosis
• the movement of a large substance into a cell by
means of a vesicle
• cell membrane folds inward creating a pouch for
the substance to enter
• once in the pouch it pinches off and forms a
vesicle
• these vesicles can fuse with lysosomes and other
organelles
Active Transport
Exocytosis
• The movement of material out of the cell by the
means of a vesicle
• Reverse process of Endocytosis
• Vesicles fuse with the cell membrane and releases
its contents to the outside of the cell
• Used to export proteins modified by the golgi
apparatus
Active Transport