Question

If the cell membrane is semi permeable, how do the substances get through the cell wall?

Answer 1

Semi permeable means it can let some molecules pass the membrane but not all

small molecules like water would easily pass through the semi permeable membrane

while large molecules like sugar will not pass through the membrane because they are too big to pass

Answer 2

It only lets some molecules pass through.

Explanation:

Small molecules like water `(H_2O)` and oxygen `(O_2)` can easily diffuse through the cell wall, since they are not big, only composed of one or two elements.

Whereas, large molecules like glucose `(C_6H_12O_6)` and nitrates `(NO_3^-)` (maybe?) cannot pass through as easily as they have to be broken down by substances such as enzymes to be smaller.

After that, they can pass through the cell wall like small molecules and be absorbed by the cell.