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Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter Presentation Transparencies Standardized Test Prep Visual Concepts Resources

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Homeostasis and Cell Transport Chapter 5 Table of Contents Section 1 Passive Transport Section 2 Active Transport

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Passive Transport Chapter 5 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Passive Transport Chapter 5 Diffusion Passive transport involves the movement of molecules across the cell membrane without an input of energy by the cell. 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 equilibrium is reached.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 5 Concentration Gradient Section 1 Passive Transport

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Passive Transport Chapter 5 Diffusion, continued Diffusion Across Membranes –Molecules can diffuse across a cell membrane by dissolving in the phospholipid bilayer or by passing through pores in the membrane.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 5 Diffusion Section 1 Passive Transport

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Passive Transport Chapter 5 Osmosis Osmosis is the diffusion of water across a membrane.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 5 Osmosis Section 1 Passive Transport

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Passive Transport Chapter 5 Osmosis, continued Direction of Osmosis –The net direction of osmosis is determined by the relative solute concentrations on the two sides of the membrane.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Passive Transport Chapter 5 Osmosis, continued Direction of Osmosis –When the solute concentration outside the cell is higher than that in the cytosol, the solution outside is hypertonic to the cytosol, and water will diffuse out of the cell.