What are the different substances that can move across the plasma membrane via facilitated diffusion and active transport? Is the following list correct?
Channel-mediated Diffusion
- small, polar molecules- hydrophilic and uncharged e.g. glucose
- ions- charged e.g. Na+
Carrier-mediated Diffusion
- large, polar molecules- hydrophilic and uncharged
Carrier Pumps (Active Transport)
- small, polar molecules- hydrophilic and uncharged
- ions- charged
I would appreciate more detail (examples) and clarity regarding size, polarity, and charge. I'm a little confused
Hey,
So you're looking at this a bit wrong, anything travelling by active transport will either travel via a carrier proteins or by bulk transport (endocytosis or exocytosis). The only things you'll really talk about as travelling via bulk transport for VCE will be proteins exported or imported into the cell, or other cells/cellular components engulfed by the cell (in immune reactions). Therefore every other type of molecule will travel via carrier proteins when it's going against the concentration gradient (when it's being actively transported) - regardless of whether it's polar, non-polar, small, large, or charged, if it's active transport it'll be going via a carrier protein.
In regards to facilitated diffusion, while some molecules can use either channel or carrier proteins generally for VCE we just refer to facilitated diffusion as being via channel proteins and active transport as being via carrier proteins. Best to check with your teacher for what they expect on SACs, but on the exam you don't need to separate what travels via channel proteins and what travels via carrier.
Note: Carrier proteins that allow facilitated diffusion of glucose are actually fairly well studied - however for VCE you don't need to know that they specifically travel via carrier proteins.
Simple diffusionI'm going to start with this because some of the things you've listed above don't need to travel via facilitated diffusion - they still do sometimes though, particularly when a cell needs a lot of them (e.g. water can travel through aquaporins).
- Small, polar molecules (e.g. water) & non polar molecules (e.g. carbon dioxide).
Facilitated diffusion- Large polar molecules (e.g. glucose)
- Charged molecules (anything represented with a + or - next to it)
Active transport (carrier proteins)- Any molecules travelling against the concentration gradient (excluding extra large molecules as below)
Active transport (Bulk transport)Concentration gradients are irrelevant for bulk transport, substances can be transported in either direction.
- Transport of very large molecules (e.g. proteins or cellular material) into or out of a cell.