Which of the following normally pass through the plasma membrane only by transport in vesicles?

Question

a. water molecules

b. sodium ions

c. proteins

d. oxygen molecules

e. hydrogen ions

and why.

I'm not cheating or trying to get an easy way out of my homework. I just have an exam tomorrow, I'm doing the questions in my book, and I don't get this one. Thanks!

Answer 1

Proteins - they are too large to pass through the membrane without a specific process/mechanism to do so.

Answer 2

c. proteins.

well, the other four molecules pass through plasma membrane via different means. water can pass through easily as it is a small molecule. O2 and H2 passes through the lipid membrane as they are uncharged, non-polar molecules. Na+ ions via sodium channels.

proteins, by vesicles because they are large. Think of endoplasmic reticulum and Golgi body. Once protein has been syntesised (in bulk) in rough e.reticulum, it is packed into vesicle and then sent to Golgi Body.