Movement across membranes

• We say that membranes are selectively permeable as they act as a barrier to most substances: allows materials to be concentratein cells, excluded, or separated from outside environment (eukaryotic also compartmentalise inside organelles)
• Molecules need to be able to enter and exit cells, there are 5 main ways substances can move across a cell membrane:

  1. Simple Diffusion
  2. Facilitated Diffusion
  3. Active Transport
  4. Osmosis
  5. Endocytosis/Exocytosis
• ATP in bulk transport: Provide energy for the vesicle movement along cytoskeleton microtubules (via motor proteins) and help fuse vesicle and plasma membrane together