Osmosis is the diffusion of water through a partially permeable membrane from an area of higher water concentration to lower concentration. It is important in plants and animals for maintaining homeostasis, or constant internal conditions. In animal cells, too little water causes cells to shrivel and too much causes them to burst. In plant cells, osmosis allows water movement into cells to swell the cytoplasm and press against cell walls, making the cells rigid and supporting stems and leaves. The fluid outside plant cells must have a higher water concentration to keep osmosis moving water into the cells.

1. Osmosis What is osmosis? Why is osmosis so important in plants and animals? Starter: What is your definition of Osmosis?

2. Osmosis is: “ the diffusion/movement of water from a high concentration (dilute solution) to a low concentration (concentrated solution) through a partially permeable membrane.” Osmosis is a special case of diffusion

3. Observation Using a model describe in your own words what is happening in this demonstration? 2. How is this happening? 3. How is this an example of osmosis/diffusion? 4. How is the colour change related to diffusion? 5. What parts if this demonstration are related to osmosis/diffusion? 6. How does diffusion compare/contrast to osmosis? 7. What ideas can you add? 8. How would you create/design a new demonstration/experiment to show osmosis? 9. What would happen if you added sugar to the solution?

4. Why is osmosis important in plants and animals? Internal concentration of cells needs to stay the same all the time for reactions to take place. Animal cells – homeostasis (maintaining constant internal conditions) - too little water an the cell will shrivel up - too much water and the cell will burst

5. Plant cells Plants need well regulated osmosis to support their stems and leaves. Water movement in makes the cytoplasm swell and press against the cell wall. Makes cell hard and rigid. Fluid outside of the cells needs to be of a higher concentration of water (dilute) to keep osmosis moving in the right direction. Substances moved against a concentration gradient are done so by active transportation.