What happens when we place gram positive cell in hypotonic solution?

Salts and sugars in solution will diffuse away from areas of high concentration into the surrounding solution. This is called simple diffusion. Water also diffuses away from areas of high free water concentration into areas of more solute concentration. Said another way, pure water diffuses into salt water and the dissolved salts in the salt water diffuse into pure water.

Cells have membranes which are permeable to water diffusion but which do not allow the salts to pass. Thus, only water can diffuse. This diffusion of water across a semi-permeable membrane is called osmosis. The membrane allows the cell to choose, by means of receptors and channels, the things it will let in and it allows the cell to hold onto the many vital substances which are dissolved in its cytoplasm.