The Cell in Action

1. The Cell in Action Exchange with the Environment

2. “Close that window! Do you want to let in all the bugs??? How do you prevent unwanted things from coming through a window? What part of a cell does the same thing?

3. Moving Cellular Materials Cells take in food, oxygen and other substances from their environments. They also release waste materials into their environments. What organelle works as a gatekeeper to let materials in and out of a cell?

4. Gatekeeper = Cell membrane . Found in both plant and animal cells, the exchange of materials between a cell and its environment takes place in the cell membrane.

5. Small particles cross the cell membrane by way of Diffusion Osmosis Passive Transport Active Transport

6. Diffusion is the movement of particles from areas of high density to areas of lower density. When the molecules are evenly spread, equilibrium occurs. To understand how materials move in and out of a cell, you need to know about diffusion….

7. Example of a diffusion in a solid: • You put a metal spoon into hot tea or coffee and the entire spoon is hot after a few minutes. • Example of diffusion in a liquid: • Adding a more dense liquid (such as corn syrup) to water • Example of diffusion in a gas: • Someone puts on too much Axe Body Spray after PE. You can smell him before AND after you see him Diffusion occurs in …. Solids Liquids Gasses

8. Osmosis is a special example of diffusion. It is the diffusion of water through a semi-permeable membrane . Semi = partial Permeable= go through, cross Osmosis

9. Osmosis Osmosis is the process by which water enters our tissues. All of our cells are surrounded by a membrane that selectively allows anything the cell needs, but prevents unwanted molecules from entering.

10. This works because the membrane contains lots of tiny holes that will let anything smaller through but obviously will stop big molecules from entering the cell. • Water is small enough to get through and enters by diffusion. • Water will enter until equilibrium is achieved. How osmosis works

11. Osmosis • If cells weren’t surrounded by water that contains few dissolved substances, the water in the cells would diffuse out of them. • Plants=wilting • However, the dissolved substances (solutes), such as salts, sugars, and other substances in the water that surrounds cells, prevent this from happening. • Equilibrium

12. Active and Passive Transport Active Transport Passive Transport • The movement of substances across the cell membranethat requires using energy by the cell • Endocytosis and Exocytosis • Low concentration to high concentration • Riding a bike up a hill! • The movement of substances across the cell membrane withoutusing energy by the cell. • Diffusion and Osmosis • High to low concentration • Coasting down a hill on your bike

13. Endocytosis The cell membrane surrounds a particle and encloses this particle in a vesicle to bring the particle into the cell A hug http://www.youtube.com/watch?v=HndmASfmI8Y Endocytosis

14. Exocytosis The cell membrane encloses a particle in the cell in a vesicle, then moves to the surface, fuses with the cell membrane, and expels the particle. Shoving someone

15. Hypertonic, Hypotonic and Isotonic • A hypertonic solution is a solution(mixture) containing more solute than solvent • A lot of salt (solute) dissolved in water (solvent) • A hypotonic solution is a solution containing more solvent than solute • Purified water --- almost no solute dissolved in the solvent (water) • An isotonic solution is a solution where the solute and solvent are equally distributed. • Cells normally want to remain in an isotonic solution, where the concentration of liquid inside is the same as the concentration of the liquid outside of it. • Equilibrium!