Biological membranes are permeable to water, but impermeable to larger molecules such as sugar.

1

• Biological membranes are permeable to water, but
  impermeable to larger molecules such as sugar.
• Membranes may be selectively permeable, allowing
  only substances of their choice into the cell.
• When a cell is at equilibrium with the
  surrounding solution, the cell is isotonic.
• Cell membranes are completely permeable to water,
  therefore, the environment the cell is exposed to
  can have a dramatic effect on the cell.

2
3 types of solutions

• Isotonic, Hypotonic and Hypertonic
• Osmosis in cells

Lets take a look!