A question in relation to movement across a cell membrane - how do you know which different ions and other substances pass through via facilitated diffusion or active transport? e.g. glucose is through active transport but calcium Ca2+ is through facilitated diffusion. Both are through either carrier proteins or protein channels. Are there a set few that we should be expected to just know ? Thank youu
I answered a similar question on the last page , here's a copy paste of it (its basically like a criterion you could follow to decide what method of movement ) :
-Simple diffusion : small molecules , hydrophobic/lipophilic, uncharged, nonpolar (eg: O2 , urea)
- Facilitated diffusion: large molecules , hydrophilic/ lipophobic , charged (including ions ) , polar (eg: glucose due to its large size and polarity)
-Active transport :for this one , it is ANYTHING going against the concentration gradient
The reason Ca2+ is through facilitated is cause its an ion , and because glucose in this situation is being taken against the concentration gradient it would be active transport. The reason they use membrane proteins is cause both facilitated and active methods utilise membrane proteins.
Also, no I don't think you would need to know a set few. Its just if a question asks you about it , it will provide hints about the structure that will allow you to answer the question. Like it might say its polar and large , and you would say facilitated .
hope this clears things up