Additional Science - Biology- Unit 2 - Osmosis

Water can move across cell membranes because of osmosis. For osmosis to happen you need:

• two solutions with different concentrations
• a partially permeable membrane to separate them

Osmosis is the movement of water from a less concentrated solution to a more concentrated solution through a partially permeable membrane.

Osmosis is important to plants. They gain water by osmosis through their roots. Water moves into plant cells by osmosis, making them turgid or stiff so they that able to hold the plant upright.

When Osmosis takes place, particles of different sizes hit the partially-permeable membrane. The smaller particles flow through the membrane, whilst the bigger particles are left where they are. The level of the more concentrated side of the partially-permeable membrane rises, while the level one with the less conctentrated side falls. When the concentration is the same on both sides of the membrane, the movement of molecules will be same in both directions. At this point, there is no futher change in the liquid levels and some of the particles have moved from one place to another because of Osmosis.