transport

• passive transport


  doesn't require energy from an external source (ATP)

  the kinetic energy that the particles possess means they are constantly in motion- motion is random
• passive transport includes

  diffusion

  facilitated diffusion

  osmosis
• diffusion

  the movement of molecules or ions from a region where they are more highly concentrated to one where concentration is lower until they are evenly distributed

  only small, non polar molecules such as oxygen and carbon dioxide would be able to freely diffuse
• facilitated diffusion

  charged ions and polar molecules would enter the cell this way.

  it uses transmembrane proteins such as channel or carrier proteins.

  It is still the movement of molecules or ions from an area of high concentration to an area of lower concentration, just through transmembrane proteins
• osmosis

  the passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a selectively permeable membrane
• water potential

  he pressure created by water molecules

  measured in kilo pascals
• active transport

  the movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins
• cotransport and absorption of glucose (+amino acids) in the ileum (small intestine)

  microvilli- creates a brush border and provides a larger surface area

  increased number of channel and carrier proteins

  diffusion only works until equilibrium is reached- cotransport is used after equilibrium has been reached
• co transport (first 2 stages)


  1. sodium ions are actively transported out of epithelial cells, by the sodium-potsium pump into the blood. This takes place in the carrier protein found in the cell surface membrane of epithelial cells
  2. this maintains a much higher concentration of sodium ions in the lumen of the intestines of the epithelial cells
• cotransport (second 2 stages)

  3. sodium ions diffuse into the epithelial cells down the concentration gradient through a cotransport protein in the cell surface membrane. As the sodium ions diffuse through the sec and carrier protein, they either carry amino acid molecules ir glucose molecules into the cell with them

  4. the glucose amino acids pass into the blood plasma by facilitated diffusion using another type of carrier
• more on cotransport

  both sodium ions and glucose/amino acid molecules move into the cell, but while the sodium ions move down their concentration gradient, the glucose molecules move against the gradient. It is the sodium ion concentration that powers movement of glucose and amino acids into the cels, rather than ATP directly. this make sit an indirect active transport rather than direct active transport