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Table of Contents

Learn about diffusion, osmosis, facilitated diffusion, ion channels, and cell membrane pumps in the process of passive and active transport across the cell membrane.

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Table of Contents

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  1. Section 1 Passive Transport Section 2 Active Transport Chapter 5 Homeostasis and Cell Transport Table of Contents

  2. Explainhow an equilibrium is established as a result of diffusion. Distinguishbetween diffusion and osmosis. Explain how substances cross the cell membrane through facilitated diffusion. Explainhow ion channels assist the diffusion of ions across the cell membrane. Section 1 Passive Transport Chapter 5 Objectives

  3. Passive transport involves the movement of molecules across the cell membrane without an input of energy by the cell. The simplest type is known as diffusion. Diffusionis the movement of molecules from an area of higher concentration to an area of lower concentration, driven by the molecules’ kinetic energy until equilibrium is reached. Equilibrium is when the concentration of molecules are the same throughout the space the molecules occupy. Section 1 Passive Transport Chapter 5 Diffusion

  4. Section 1 Passive Transport Chapter 5 Concentration Gradient Click below to watch the Visual Concept. Visual Concept

  5. Diffusion Across Membranes Molecules can diffuse across a cell membrane by dissolving in the phospholipid bilayer or by passing through pores in the membrane. Section 1 Passive Transport Chapter 5 Diffusion, continued

  6. Section 1 Passive Transport Chapter 5 Diffusion

  7. Osmosisis the diffusion of water across a membrane. Section 1 Passive Transport Chapter 5 Osmosis

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

  9. Direction of Osmosis The net direction of osmosis is determined by the relative solute concentrations on the two sides of the membrane. If the salt concentration is higher inside the cell, water is going to diffuse into the cell (this process is called osmosis) until equilibrium is reached. Section 1 Passive Transport Chapter 5 Osmosis, continued

  10. Direction of Osmosis When the solute concentration of molecules outside the cell is higher than that in the cytosol, the solution outside ishypertonicto the cytosol, and water will diffuse out of the cell. When the solute concentration of molecules outside the cell is lower than the concentration in the cytosol, the solution outside is hypotonic to the cytosol, and water will diffuse into the cell. Section 1 Passive Transport Chapter 5 Osmosis, continued

  11. Direction of Osmosis When the solute concentrations outside and inside the cell are equal, the solution outside isisotonic, and there will be no net movement of water. Section 1 Passive Transport Chapter 5 Osmosis, continued

  12. Section 1 Passive Transport Chapter 5 Hypertonic, Hypotonic, Isotonic Solutions

  13. Hypertonic, Isotonic, and Hypotonic

  14. Section 1 Passive Transport Chapter 5 Comparing Hypertonic, Isotonic, and Hypotonic Conditions Click below to watch the Visual Concept. Visual Concept

  15. 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. Contractile vacuoles are organelles that regulate water levels in paramecia. Section 1 Passive Transport Chapter 5 Osmosis, continued

  16. Animal cells, and most plant cells, live in hypotonic environments. Plant cells take in water from their environment until the cell membrane pushes against the cell wall. The pressure that water molecules exert against the cell wall is called turgor pressure. In hypertonic environments, water leaves the plant cells causing the cell membrane to pull away from the cell wall in a condition called plasmolysis. Section 1 Passive Transport Chapter 5 Osmosis, continued

  17. In facilitated diffusion, a molecule binds to a carrier protein on one side of the cell membrane. The carrier protein then changes its shape and transports the molecule down its concentration gradient to the other side of the membrane. Section 1 Passive Transport Chapter 5 Facilitated Diffusion

  18. Section 1 Passive Transport Chapter 5 Facilitated Diffusion

  19. Ion channelsare proteins, or groups of proteins, that provide small passageways across the cell membrane through which specific ions can diffuse. Section 1 Passive Transport Chapter 5 Diffusion Through Ion Channels

  20. Section 1 Passive Transport Chapter 5 Ion Channels

  21. Section 2 Active Transport Chapter 5 Objectives • Distinguish between passive transport and active transport. • Explainhow the sodium-potassium pump operates. • Compareendocytosis and exocytosis.

  22. Section 2 Active Transport Chapter 5 Cell Membrane Pumps • Active transportmoves 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.

  23. Section 2 Active Transport Chapter 5 Cell Membrane Pumps, continued • 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 pumpmoves three Na+ ions into the cell’s external environment for every two K+ ions it moves into the cytosol. • ATP supplies the energy that drives the pump.

  25. Section 2 Active Transport Chapter 5 Sodium-Potassium Pump

  26. Sodium-Potassium Pump1. 3 Na+ ions located in the cytosol bind to the carrier protein2. A phosphate group is removed from ATP and bounds to the carrier protein3. The binding of the phosphate group changes the shape of the carrier protein, allowing the 3 Na+ ions to be released to the outside of the cell4. 2 K+ ions located outside the cell bind to the carrier protein5. The phosphate group is released, restoring the original shape of the carrier protein so that the 2 K+ ions are released into the cytosol6. The cycle is now ready to be repeated

  27. Section 2 Active Transport Chapter 5 Movement in Vesicles • Endocytosis • In endocytosis, cells ingest external materials by folding around them and forming a pouch. • The pouch then pinches off and becomes a membrane-bound organelle called a vesicle.

  28. Section 2 Active Transport Chapter 5 Movement in Vesicles, continued • Endocytosis • Endocytosis includespinocytosis, in which the vesicle contains solutes or fluids, and phagocytosis, in which the vesicle contains large particles or cells.

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

  30. 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.

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

  32. Section 2 Active Transport Chapter 5 Endocytosis and Exocytosis

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