Download Chapter 5 Section 1 Passive Transport

Chapter 5
Homeostasis and Cell Transport
Table of Contents
Section 1 Passive Transport
Section 2 Active Transport
Chapter 5
Section 1 Passive Transport
Objectives
• Explain how an equilibrium is established as a result
of diffusion.
• Distinguish between diffusion and osmosis.
• Explain how substances cross the cell membrane
through facilitated diffusion.
• Explain how ion channels assist the diffusion of ions
across the cell membrane.
Chapter 5
Section 1 Passive Transport
Standards
SPI 3210.1.7 Predict the movement of water and other
molecules across selectively permeable membranes.
SPI 3210.1.8 Compare and contrast active and passive
transport.
 3210.1.8 Analyze experimental data to distinguish
between active and passive transport.
CLE 3210.1.5 Compare different models to explain the
movement of materials into and out of cells.
Chapter 5
Section 1 Passive Transport
Passive Transport
•Involves the movement of molecules across the cell membrane
•without an input of energy by the cell.
• NO ENERGY REQUIRED to move substances
across membrane -- water, lipids, and other lipid
soluble substances.
• Types:
– Diffusion
– Osmosis
– Facilitated Diffusion
– Filtration
Chapter 5
Section 1 Passive Transport
Diffusion
• Diffusion is the movement of molecules from an area
of higher concentration to an area of lower
concentration, driven by the molecules’ kinetic energy
until a state of dynamic equilibrium* is reached.
– Concentration gradient, i.e., the difference in
concentration across space.
• Occurs because of Brownian Motion, i.e., the random
movement of particles.
*Dynamic equilibrium – continued movement of molecules
with no net change in concentration
Chapter 5
Section 1 Passive Transport
Concentration Gradient
Click below to watch the Visual Concept.
Chapter 5
Diffusion
Section 1 Passive Transport
Chapter 5
Osmosis
• Osmosis is the
diffusion of
water across a
membrane.
Section 1 Passive Transport
Chapter 5
Section 1 Passive Transport
Osmosis
Click below to watch the Visual Concept.
Chapter 5
Section 1 Passive Transport
Osmosis, continued
• Direction of Osmosis
– The net direction of osmosis is determined by the
relative solute concentrations on the two sides of
the membrane.
Chapter 5
Section 1 Passive Transport
Osmosis, continued
• Direction of Osmosis
– When the solute concentration outside the cell is
higher than that in the cytoplasm, the solution
outside is hypertonic (more solute, less water) to
the cytoplasm, and water will diffuse out of the
cell.
– Plasmolysis = cell’s shrinking due to water loss
Chapter 5
Section 1 Passive Transport
Osmosis, continued
• Direction of Osmosis
– When the solute concentration outside the cell is
lower than that in the cytosol, the solution outside
is hypotonic (less solute, more water) to the
cytosol, and water will diffuse into the cell.
– Cytolysis = cell’s bursting due to water gain
Chapter 5
Section 1 Passive Transport
Osmosis, continued
• Direction of Osmosis
– When the solute concentrations outside and inside
the cell are equal, the solution outside is isotonic
(same solute, same water), and there will be no
net movement of water.
Chapter 5
Section 1 Passive Transport
Hypertonic, Hypotonic, Isotonic Solutions
Chapter 5
Section 1 Passive Transport
Osmosis, continued
• How Cells Deal With Osmosis
– To remain alive, cells must compensate for the
water that enters the cell in hypotonic
environments and leaves the cell in hypertonic
environments.
– Cells in multicellular organisms respond to
hypotonic environments by pumping solutes out of
the cytosol (RBCs cannot compensate for
changes in solute concentration)
– Contractile vacuoles are organelles that regulate
water levels in paramecia.
Chapter 5
Section 1 Passive Transport
Facilitated Diffusion
• Diffusion of molecules across a membrane when they
are not soluble in lipids or are too large (e.g. glucose)
to pass through pores in membrane
• In facilitated diffusion, a molecule binds to a carrier
protein on one side of the cell membrane.
• The carrier protein (specific for one type of molecule)
then changes its shape and transports the molecule
down its concentration gradient to the other side of
the membrane.
Chapter 5
Section 1 Passive Transport
Facilitated Diffusion
Chapter 5
Section 1 Passive Transport
Diffusion Through Ion Channels
• Ion channels are proteins, or groups of proteins, that
provide small passageways across the cell
membrane through which specific ions can diffuse.
• Ions important in cell function include sodium,
potassium, calcium, and chloride
Chapter 5
Ion Channels
Section 1 Passive Transport
Chapter 5
Section 2 Active Transport
Crash Course #5
Cell Membranes and Transport
Chapter 5
Section 2 Active Transport
Objectives
• Distinguish between passive transport and active
transport.
• Explain how the sodium-potassium pump operates.
• Compare endocytosis and exocytosis.
Chapter 5
Section 1 Passive Transport
Standards
SPI 3210.1.7 Predict the movement of water and other
molecules across selectively permeable membranes.
SPI 3210.1.8 Compare and contrast active and passive
transport.
 3210.1.8 Analyze experimental data to distinguish
between active and passive transport.
CLE 3210.1.5 Compare different models to explain the
movement of materials into and out of cells.
Chapter 5
Section 2 Active Transport
Cell Membrane Pumps
• Active transport moves molecules across the cell
membrane from an area of lower concentration to an
area of higher concentration.
• Unlike passive transport, active transport requires
cells to expend energy.
• Some types of active transport are performed by
carrier proteins called cell membrane pumps.
Chapter 5
Section 2 Active Transport
Cell Membrane Pumps, continued
• Sodium-Potassium Pump
– The sodium-potassium pump moves three Na+
ions into the cell’s external environment for every
two K+ ions it moves into the cytoplasm.
• Animal cells must have a higher concentration of Na+
ions outside the cell and a higher concentration of K+
ions inside the cell
– ATP supplies the energy that drives the pump.
Chapter 5
Section 2 Active Transport
Sodium-Potassium Pump
Chapter 5
Section 2 Active Transport
Sodium-Potassium Pump
• The exchange of three Na+ ions for two K+ ions
creates an electrical gradient across the cell
membrane
– Outside becomes positively charged relative to the
inside, which becomes negative
• Difference in electrical charge is important for
the conduction of electrical impulses along
nerve cells
Chapter 5
Section 2 Active Transport
Movement in Vesicles
•
Endocytosis
– In endocytosis, cells ingest external fluid,
macromolecules, and large particles, including
cells by folding around them and forming a
pouch.
– The pouch then pinches off and becomes a
membrane-bound organelle called a vesicle.
*Some vesicles fuse with lysosomes, and
their contents are digested by lysosomal
enzymes
Chapter 5
Section 2 Active Transport
Movement in Vesicles, continued
• Endocytosis
– Endocytosis includes pinocytosis, in which the
vesicle contains solutes or fluids, and
phagocytosis, in which the vesicle contains large
particles or whole cells.
• Bacteria and viruses are ingested in this way
– Receptor-mediated endocytosis – molecules are
brought into the cell via coated pits (proteins)
Chapter 5
Section 2 Active Transport
Movement in Vesicles, continued
• Exocytosis
– In exocytosis, vesicles made by the cell fuse with
the cell membrane, releasing their contents into
the external environment.
• Used to release large molecules, such as
proteins, waste products, or toxins that would
damage the cell if they were released within the
cytoplasm
Chapter 5
Section 2 Active Transport
Exocytosis and Endocytosis
Click below to watch the Visual Concept.
Visual Concept
Chapter 5
Section 2 Active Transport
Endocytosis and
Exocytosis