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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”
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

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


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.