The function of the membrane is to let the water and small molecules pass through while retaining the protein.

Small molecules can pass through it, so the shell allows gas exchange for the growing embryo.

If there are a lot of branches, only small molecules can pass through.

If there are few branches, big molecules can pass through.

However, since the larger molecules will have a tougher time going through the channels, the large molecules will pass outside the spheres.

Also, negatively charged molecules will pass through far less frequently than positively charged ones.

Smaller molecules can pass through a pore and then pass through another one.

The larger molecules simply pass by the pores as they are too large to enter the pores.

They form hexagonal pores or channels through which ions, sugars, and other small molecules can pass.

It also has narrow channels; through which only molecules having dimensions within certain limits can pass.