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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

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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

What affects the rate of diffusion

What affects the rate of diffusion?



  • Diffusion of water across a semi-permeable membrane

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

Osmotic pressure

Osmotic Pressure

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.

Evolution of multicellular organisms

Evolution of Multicellular Organisms

Some bacteria were more useful confined and alive than as food

Some Bacteria were more useful “confined and alive” than as food

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