Table of Contents

1
Table of Contents
Homeostasis and Cell Transport
Chapter 5

• Section 1 Passive Transport
• Section 2 Active Transport

2
Objectives
Section 1 Passive Transport
Chapter 5

• 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.

3
Standards
Section 1 Passive Transport
Chapter 5

• 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.
  

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Passive Transport
Chapter 5
Section 1 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

5
Diffusion
Section 1 Passive Transport
Chapter 5

• 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

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Section 1 Passive Transport
Chapter 5
Concentration Gradient
Click below to watch the Visual Concept.
7
Diffusion
Section 1 Passive Transport
Chapter 5
8
Osmosis
Section 1 Passive Transport
Chapter 5

• Osmosis is the diffusion of water across a
  membrane.

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Section 1 Passive Transport
Chapter 5
Osmosis
Click below to watch the Visual Concept.
10
Osmosis, continued
Section 1 Passive Transport
Chapter 5

• Direction of Osmosis
• The net direction of osmosis is determined by the
  relative solute concentrations on the two sides
  of the membrane.

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Osmosis, continued
Section 1 Passive Transport
Chapter 5

• 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 cells shrinking due to water loss

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Osmosis, continued
Section 1 Passive Transport
Chapter 5

• 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 cells bursting due to water gain

13
Osmosis, continued
Section 1 Passive Transport
Chapter 5

• 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.

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Hypertonic, Hypotonic, Isotonic Solutions
Section 1 Passive Transport
Chapter 5
15
Osmosis, continued
Section 1 Passive Transport
Chapter 5

• 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.

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Facilitated Diffusion
Section 1 Passive Transport
Chapter 5

• 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.

17
Facilitated Diffusion
Section 1 Passive Transport
Chapter 5
18
Diffusion Through Ion Channels
Section 1 Passive Transport
Chapter 5

• 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

19
Ion Channels
Section 1 Passive Transport
Chapter 5
20
Section 2 Active Transport
Chapter 5
Crash Course 5 Cell Membranes and Transport
21
Section 2 Active Transport
Chapter 5
Objectives

• Distinguish between passive transport and active
  transport.
• Explain how the sodium-potassium pump operates.
• Compare endocytosis and exocytosis.

22
Standards
Section 1 Passive Transport
Chapter 5

• 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.
  

23
Section 2 Active Transport
Chapter 5
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.

24
Section 2 Active Transport
Chapter 5
Cell Membrane Pumps, continued

• Sodium-Potassium Pump
• The sodium-potassium pump moves three Na ions
  into the cells 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.

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Sodium-Potassium Pump
Section 2 Active Transport
Chapter 5
26
Sodium-Potassium Pump
Section 2 Active Transport
Chapter 5

• 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

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Section 2 Active Transport
Chapter 5
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

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Section 2 Active Transport
Chapter 5
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)

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Section 2 Active Transport
Chapter 5
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

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Section 2 Active Transport
Chapter 5
Exocytosis and Endocytosis
Click below to watch the Visual Concept.
Visual Concept
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Endocytosis and Exocytosis
Section 2 Active Transport
Chapter 5