Living Cells

1. Living Cells Diffusion and Osmosis

2. Diffusion and Osmosis • In order to stay alive cells must be able to transport water and other substances in and out. • Substances useful to cell move IN • Substances which are waste move OUT • Two vital processes for both animal and plant cells are osmosisand diffusion.

3. Diffusion • This is the movement of molecules of a substance through a selectively permeable membrane, from a region of high concentration to a region of low concentration along a concentration gradient, until evenly spread. • See sheets page 9.

4. Osmosis • This is the movement of WATER molecules through a selectively permeable membrane, from a region of high concentration to a region of low concentration along a concentration gradient, until evenly spread.

5. Selectively Permeable Membrane • The cell membrane contains small pores. • See sheet page 11. • The movement of molecules depends on; • Pore size • Molecule size • HC to LC

6. Concentration Gradient • The difference in concentration that exists between a region of high concentration and a region of low concentration. • During diffusion and osmosis movement of molecules always occurs down a concentration gradient, from HC to LC.

7. Concentration Gradient

8. Concentration • Examples; • A 10% sugar solution contains : 10% sugar and 90% water. • A 30% salt concentration contains: 30% salt and 70% water. ect.

9. Diffusion in action • Which direction would glucose move if inside the cell has a 20% glucose solution, and outside in the beaker has a 40% glucose solution?

10. Osmosis in action • Which direction would water move if inside the cell has a 20% sugar solution, and outside in the beaker has a 10% sugar solution?

11. Relative water concentration • When two solutions have a different water concentration, the solution with the highest water concentration is said to be hypotonic. • The one with the lower concentration is said to be hypertonic. • Since pure water has the highest possible water concentration, it is said to be hypotonic to all other solutions. • When two solutions are found to have the same water concentration, we say they are isotonic to one another. • See sheets page 12.

12. Unicellular organisms • (eg. Paramecium, animal cell) – See sheets page 9. • Oxygen is constantly being used up as the animal respires. • This means that oxygen conc. inside the cell is lower than outside. • Oxygen will enter by diffusion. • As respiration occurs, oxygen is used up and carbon dioxide is produced. • Carbon dioxide will leave the cell as a waste product by diffusion.

13. Multicellular organisms • (eg. mammals) - see sheets page 10. • In mammals diffusion plays an important rolein the movement of oxygen entering the lungs, passing to the air sacs (alvioli), to the blood capillaries and then to the body cells. • Carbon dioxide moves out in the opposite direction.

14. Osmosis in potato cells • Activity 1.6 (See sheets page 12) • Passage answers page 13; • In your experiment with potato cells, an overall movement of water molecules occurred from a region of high water concentration (hypotonic) to a region of low water concentration (hypertonic) through the cell membrane. • The cell membrane prevents larger molecules like sugar from diffusing across it because it only contains small pores. A membrane which only lets small molecules through like water and not larger molecules is called a selectively permeable membrane. The movement of water through this selectively permeable membrane is called osmosis.