Imagine a tea bag, the bags walls are porous (holes in them) just like a membrane.
The
water displaces inside the bag, now although this has a lot to do with environmental pressure (ie. the
water) it is mostly to do with diffusion, Osmosis is a form of diffusion*, specifically across a
semi - permeable (porous) membrane.
*
Diffusion is displacement of molecules so that they are equal.
E.g. Imagine your friend sprays deodorant/perfume on the far side of the room, it takes a couple of seconds to reach you.
It is a highly concentrated
cloud at first but then spreads (diffuses) into the air until there are an EQUAL concentration of
spray to the air.
E.g. five 1 pennies to every three 2 pennies