Question

Who am I l am single layered, but maintain cellular osmotic pressure

Answer 1

semipermeable membrane

Answer 2

As it's single layered then the first two priorities i.e cell membrane and cell wall can be removed because both are multilayered and cell wall can't help maintaining cellular osmotic pressure.

It must be a semi-permeable membrane ( and not selectively permeable membrane).

Single layered cellulose membrane is a good example of single-layered semi permeable membrane.