1. Diffusion and Osmosis

2. Homeostasis To maintain homeostasis cells regulate what enters and leaves the cell The main “controller” is the cell membrane Substances can cross with or without energy Passive verses active transport Depends on the size and type of molecule

3. Diffusion Diffusion: the movement of molecules from an area of higher concentration to an area of lower concentration Based on the principle of a concentration gradient Difference in the concentration of a substance across a space Substances diffuse down their concentration gradient Movement continues until an equilibrium is reached Passive process Does not require energy Typically small non-polar molecules

4. Diffusion - Start

5. Diffusion - Equilibrium

6. Diffusion - Solutions

7. Osmosis Osmosis is a specialized form of diffusion Definition: movement of water across a membrane Water flows to the area with higher concentration of dissolved particles/substances Water still moves down its concentration gradient Water can flow into or out of cells Water gradient creates Osmotic Pressure The force or strength of osmosis Often viewed as the pressure within a cell Helps support plant cells

8. How many water molecules are on the left? Right? Which side has a higher solute concentration? Which way will the water move? Why?

9. Types of Solutions Hypertonic, Hypotonic, & Isotonic – relates to concentration of dissolved particles in water Hyper – “over”, ex. higher conc. of particles, less ‘free’ water Hypo – “lower” Iso – “same” Descriptions refer to the concentration outside of the cell

10. Labels refer to the solute concentration outside of the cell

11. Hypotonic Solutions There is a lower concentration of solute outside of the cell Water moves into the cell Cell swells and can even burst (lyse) Some plant and bacteria cells have cell walls that prevent this Some cells release water or even particles to reduce osmotic pressure 90% H 2 O 10% solute 85% H 2 O 15% solute

12. Hypertonic Solutions There is a higher concentration of solute outside of the cell Water moves out of the cell Cell shrinks 90% H 2 O 10% solute 95% H 2 O 5% solute

13. Isotonic Solutions The concentration of solutes is the same in both the cell and the solution The water diffuses into and out of the cell at the same rate iso = same Cell maintains its same size 90% H 2 O 10% solute 90% H 2 O 10% solute

14. What does it mean? The type of solution cause different situations in plants and animals Plants like hypotonic solutions to maintain pressure against the cell wall Animals like isotonic solutions

15. Contractile Vacuoles An organelle in microorganisms that excretes excess water Collect Water  contract  squeeze water out

16. Explain the caption…

17. Study the diagram below. It represents a container divided by a semi-permeable membrane. A different solution in its initial state is shown on each side of the membrane Describe which molecule(s) will move through the membrane and which molecule(s) will not. Describe the relative rates at which the molecule(s) will move across the membrane. Describe in which direction the molecule(s) will move. Describe how long the molecule(s) will continue to move