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Cell Membrane and Cell Transport Mechanisms

Explore the structure and functions of cell membranes, including passive and active cell transport processes such as diffusion, osmosis, facilitated diffusion, endocytosis, and exocytosis. Learn how these mechanisms maintain cellular homeostasis and enable the movement of materials in and out of cells.

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Cell Membrane and Cell Transport Mechanisms

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  1. Cell Membrane & Cell Transport

  2. Cell Membrane Cell Wall Cell membrane Cell membrane vs. cell wall All cells have cell membranes Flexible barrier Function: maintain homeostasis within the cell

  3. protein channel Layer 1 Cell Membrane Layer 2 lipid bilayer protein pump Cell membrane structure • Many names… cell membrane, plasma membrane, phospholipid bilayer • Phospholipid bilayer – two layers of phospholipids with embedded proteins

  4. Cell membrane structure Hydrophilic head – “water loving” attracts water Hydrophobic tail – “water fearing” repels water Creates a constant push and pull Phosopholipid Bilayer

  5. Cell membrane structure Small materials can pass easily: Push and pull of water Porous nature Vibrating phospholipids, creating openings Phosopholipid Bilayer

  6. Cell membrane structure “Fluid Mosaic Model”: explains the structure of the cell membrane Proteins and other embedded materials “float” within the cell membrane

  7. Cell membrane structure Carbohydrate Chain Cholesterol Phospholipid Bilayer Membrane Protein Transport/Channel Proteins

  8. Cell membrane Function • “Gatekeeper” • Semipermeable : Allows certain materials in and out of the cell • Nutrients IN • Waste OUT • CELL TRANSPORT: MOVEMENT OF MATERIALS IN AND OUT OF CELLS

  9. Cell transport • The movement of materials in and out of cells (cell transport) … can be passive or active • Passive Transport: Does NOT require energy • Active Transport: Requires energy

  10. Cell transport • Passive Transport • Does NOT require energy • Movement of materials from HIGH  LOW • “with the concentration gradient” • Diffusion, Osmosis, Facilitated Diffusion

  11. Cell transport • Active Transport • REQUIRES the use of energy • Movement of materials from LOW  HIGH • “against the concentration gradient” • Endocytosis and Exocytosis

  12. Passive Transport - diffusion Diffusion: movement of small particles from high to low until equilibrium is reached

  13. Passive Transport - diffusion Diffusion: movement of small particles from high to low until equilibrium is reached Particles are small enough to pass through the porous cell membrane

  14. Passive Transport - OSMOSIS Osmosis: the diffusion of water across a selectively permeable membrane Outside Cell Water will travel from HIGH concentration  LOW concentration Inside Cell

  15. Passive Transport - OSMOSIS Osmosis: the diffusion of water across a membrane Water travels from high  low Osmosis will take place until equilibriumis reached 25% sugar 75% water 60% sugar 40% water 50% sugar 50% water 50% sugar 50% water

  16. Passive Transport - OSMOSIS Osmosis: the diffusion of water across a membrane Water will move in and out of cells when they are placed in various solutions

  17. Passive Transport - OSMOSIS Isotonic Solution – equal amount of solute in and out of cell. Water moves in and out of cell in equal amounts Cell size does not change

  18. Passive Transport - OSMOSIS Hypertonic Solution – higher concentration of solute outside cell. Water diffuses out of cell through osmosis. Cell shrinks/shrivels in size.

  19. Passive Transport - OSMOSIS Hypotonic Solution – higher concentration of solute inside cell. Water diffuses into cell through osmosis. Cell expands and can even burst.

  20. Glucose molecules outside of cell inside of cell Passive Transport – facilitated diffusion Facilitated Diffusion – Diffusion of larger molecules which must be “helped” through the membrane by traveling through channel proteins & carrier proteins High  Low! No energy!

  21. Outside cell Inside cell squeezing motion “bridge”

  22. Active Transport review • Active Transport • REQUIRES the use of energy • Movement of materials from LOW  HIGH • “against the concentration gradient” • Endocytosis and Exocytosis

  23. Active Transport - endocytosis Endocytosis – the movement of large molecules INTO the cell Low  High Requires energy

  24. Active Transport - endocytosis Molecule “bumps” into cell membrane Cell membrane wraps around and engulfs particle Creates a temporary vesicle/vacuole for transport

  25. Active Transport - endocytosis • Examples: • Your white blood cells use energy to engulf bacteria • An amoeba bumps into something tasty!

  26. A white blood cell chasing a bacterium https://www.youtube.com/watch?v=JnlULOjUhSQ

  27. Active Transport - exocytosis Exocytosis – the movement of large molecules OUT OF the cell Low  High Requires energy

  28. Active Transport - exocytosis The golgi body plays a major role in the secretion (release) of proteins and other materials through exocytosis

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