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Cell Transport. Modern Biology Chapter 5. Passive transport. Transport across a membrane without the expense of energy Video. Equilibrium. Equal concentration of molecules of a substance throughout a space All things move toward equilibrium unless energy is added. Diffusion.

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Cell transport

Cell Transport

Modern Biology Chapter 5

Passive transport
Passive transport

  • Transport across a membrane without the expense of energy

  • Video


  • Equal concentration of molecules of a substance throughout a space

  • All things move toward equilibrium unless energy is added


  • random movement of molecules

  • Involves molecules that are small enough to fit between the phospholipids

  • Molecules move from areas of higher concentration to areas of lower concentration

  • Example: perfume or food dye


  • Diffusion of water across a semi-permeable membrane

  • Water moves from areas of high water concentration to areas of lower water concentration

Osmotic pressure1
Osmotic pressure

  • Hypertonic

    • [solute] inside cell < [solute] outside cell

    • Water moves out of cells

    • Cell collapses

    • Video

Osmotic pressure2


[solute] outside cell < [solute] inside cell

Water moves into cells

Cell explodes

Osmotic pressure

Osmotic pressure3
Osmotic pressure

  • Isotonic: water levels are even inside and outside cell

    • [solute] outside cell = [solute] inside cell

    • Cell remains in balanced equilibrium

Osmotic pressure4
Osmotic pressure

  • Cells attempt to prevent death due to osmotic pressure in a number of ways

    • Cell wall: rigid cell wall prevents membrane from rupturing (turgor pressure)

    • Pump out water: specialized organelles called vacuoles remove excess water

    • Bathe cells in blood: blood is fairly isotonic with cells

Facilitated diffusion
Facilitated diffusion

  • Diffusion of specific molecules

  • Works with the aid of carrier proteins

  • Each carrier protein is molecule specific

  • Diffusion through ion channels

  • Facilitated diffusion flick

Ion channels
Ion channels

  • allow passage of ions

  • ions are not lipid soluble so they need help

  • each specific to one kind of ion

  • may always be open or have “switches”

Active transport

Active Transport

Active Transport

Example na k pump
Example: Na+/K+ pump

  • Cells pump Na+ out and K+ in

  • For every 3 Na+ that exit cell, 2 K+ enter

  • Ions affect shape of protein causing the appropriate channels to open and close.

  • Creates a charge across the membrane

    • Outside membrane has + charge

    • Inside membrane has a – charge

    • Allow for electrical conduction

    • Sodium potassium pump

    • Another Na+/K+ pump

Active transport1
Active transport

  • Movement across a semi-permeable membrane that requires the use of energy

  • Used to move molecules against the concentration gradient

  • Video

Active transport2
Active Transport

  • Endocytosis: movement of large molecules into cell by pinching off of the cell membrane

  • Pinocytosis: movement of water

  • Phagocytosis: movement of solids

  • Exocytosis: endocytosis in reverse

  • Endo and Exocytosis

  • ER and Golgi animation

  • Internal Transport

Cell transport

  • Transport movies

  • More transport

  • Cotransport

  • The Inner Life of Cells

  • Inner Life with Narrative

Evolution of multi cellular organization
Evolution of multi-cellular organization

The origin of eukaryotic cells

The endosymbiont theory: Lynn Margulis

Cell transport

Stromatolites are good evidence

Stromatolites and their close cousins the thrombolites, are rock-like buildups of microbial mats that form in limestone- or dolostone-forming environments.