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1. Add to table of contents Osmosis Drawings Pg. 34 Cell Membrane & Tonicity Pg. 35

2. Cell Membrane and Tonicity Pg. 35

3. Cell Membrane Functions • Controls the flow of nutrients in & out of cell. • Maintains homeostasis • Selectively Permeable: allows some substances to cross more easily than others.

4. Cell Membrane Structure • Composed of: • 1. Phospholipid Bilayer:double layer. • A. Head: Hydrophilic (“water-loving”) • B. Tails: Hydrophobic (“water-fearing”) • 2. Proteins: act as channels or pumps to move substances in & out. • 3. Carbohydrates:act as ID tags for other cells.

5. Diffusion • Diffusion: the movement of molecules from an area of higher concentration to an area of lesser concentration. • Eventually evens out (“Equilibrium”) • Does NOT require any energy • Concentration Gradient: the difference in concentrations inside and outside a cell.

6. Osmosis • Osmosis: the diffusion of water across a membrane. • Does NOT require energy. (is passive) • Whether water moves into or out of the cell depends on solute concentrations. • Solutes = salt, sugars, proteins, etc.

7. Isotonic Solutions • Isotonic: solute concentrations are equal on both sides of cell membrane. • Water will osmose IN & OUT of cell equally. • Most cells exist in isotonic solutions.

8. Hypertonic Solutions • Hypertonic: more solute outside cell than inside. • i.e.: a weak/dilute solution inside cell. • Water will move OUT of cell. • May cause animal cells to shrivel up & die. • Causes plants to wilt.

9. Hypotonic Solutions • Hypotonic: less solute outside cell than inside. • i.e.: a strong solution inside cell. • Water will move INTO cell. • May cause animal cells to swell & burst. • Cell walls keep plant cells from bursting.

10. Tonicity – Do tonicity drawings