What is osmosis (and how is it different to diffusion and active transport)?
Osmosis is diffusion of water
Osmosis is the diffusion / movement of water from a high to low concentration of water through a semi-permeable membrane (i.e. down a concentration gradient). So requires no energy to occur.
A semi- permeable membrane only allows small molecules (in thus case, water) to pass through, so large molecules such as sugar cannot pass.
Active transport is the net movement of molecules / particles from a low to high concentration (i.e. up a concentration gradient) and so requires energy for this to occur.