Membrane Transport

Endocytosis
1. fluidity of membrane
  1. allows materials to be taken in
  2. allows structures surrounded by membrane to change shape and structure
2. vesicles pinched off from membranes
  1. done by proteins in membrane using ATP
  2. forms inside plasma membrane
  3. carries materials from outside
3. contents
  1. water
  2. solutes
  3. molecules too large to pass through membrane
  4. sometimes large undigested food particles
  5. sometimes pathogens to kill
Vesicle movement in cells
1. vesicle
  1. small sac of membrane with drop of fluid inside
  2. spherical
  3. present in eukaryotic cells usually
  4. called contractile vacuole
2. move materials within cells
3. movement of cell contents or proteins
Exocytosis
1. fluidity of membrane
  1. allows materials to be released
  2. vesicle fuses with plasma membrane; contents out of cell
  3. digestive enzymes released
  4. expel waste products
Simple diffusion
1. moves particles across membrane
2. higher concentration to lower concentration down concentration gradient
3. passive process
4. particles pass between phospholipids in membrane
5. non-polar particles enter easily
6. polar particles can enter at low rates
7. smaller the easier
Facilitated diffusion
1. particles move across membrane
2. particles that cannot diffuse pass through a channel in membrane
3. channels
  1. holes with narrow diameter
  2. protein walls
  3. diameter and chemicals ensure only one type enters
4. high conc to low conc
Osmosis
1. particles move across membrane
2. net water movement
3. low conc solute to high conc
4. passive
5. water channels aquaporins
  1. narrowest point - slightly larger than water molecules
  2. positive charge prevents proton entry
6. small enough to flow freely through membrane
Active transport
1. particles move across membrane
2. against conc gradient
3. requires ATP
4. carried out by pump proteins
5. allows cell to control cytoplasm
6. pumped in from central chamber

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