Questions Describe how the cell membrane helps maintain homeostasis. Explain what affect more cholesterol would have on the cell membrane. Explain what the proteins in the cell membrane do. 1

Describe the structure of the cell membrane. Agenda for Wednesday Nov 16 th 1.Diffusion/osmosis notes 2.Start Lab 3.Demo 4.Look at Elodea All late work is due Nov 29 th Membrane, osmosis, diffusion QUIZ Friday 2

Concentration Solute – stuff we want to dissolve Solvent – substance in which we dissolve something Concentration – amount of a solute dissolved in a given volume of solution – A lot of solute is called concentrated – Little solute is called dilute 3

Diffusion Particles in gases, liquids, and solids are in constant motion – Substances in water move in a random motion called Brownian motion Diffusion – movement of particles from high concentration to low concentration – No energy 4

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Diffusion Flow of particles eventually reaches equilibrium – Particles continue to flow but no change in concentration on each side Larger particles move slower (large mass) – Collide with other particles Hotter particles move faster (more energy) 6

Diffusion and Membrane Membrane has selective permeability – Not all particles can pass through – Polar/nonpolar lipid bilayer Cannot pass through: Ions (salts dissolved in water) Hydrophilic molecules (glucose) Macromolecules 7

Facilitated Diffusion Proteins in the membrane move ions and small molecules across membrane 8

Carrier Proteins proteins change shape as molecule enters 9

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Osmosis Diffusion of water across a membrane 11

Osmosis Isotonic – concentration of solute is the same inside the cell and outside – Water enters and leaves at same rate – Cell is normal 12

Osmosis Hypotonic – more solute inside cell – more water outside cell – Cells gain water – Animal cells can burst – Cell wall prevents plant cells from rupturing The osmotic pressure, turgor pressure, supports the cell 13

Osmosis Hypertonic – more solute outside cell – Cells lose water – Animal cells shrivel up – Plants: membranes pulls away from the cell wall The cell wall is rigid and does not shrink 14

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Active Transport Def. – substances move from low to high concentrations – Need energy – Use carrier proteins 16

Na/K ATPase Pump Found in animal cells Helps maintain levels of sodium and potassium Uses energy (ATP) to move 3 Na ions out of the cell and 2 K into the cell High levels of sodium on outside creates a gradient 17

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Coupled Transport Linked, simultaneous transport of two substances across a cell membrane As sodium moves to one side it creates a high concentration gradient – This allows protein channels to open allowing other particles (sucrose/sugar) to move across membrane – Spend very little energy 19

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Transport of Large Particles Endocytosis – c ell surrounds a substance in the outside environment and brings it into the cell 21

Transport of Large Particles Exocytosis – secretion of materials at the plasma membrane – Expels waste, secrete substances (such as hormones) produced by cell 22

What is diffusion? Osmosis? Agenda for Thursday Nov 17 th 1.Review 2.Start lab 3.Demo 4.Practice stuff Osmosis, diffusion, cell membrane, other QUIZ tomorrow All Late work due Nov 29 th 23