Describe the cell membrane and its components. Agenda for Wednesday Feb 16 th 1.Finish work from yesterday 2.Diffusion and Osmosis 1.Starch Demo and Questions 1

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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. 4

Concentration Substance dissolved in something is called a solute What a solute is dissolved in is called a solvent Concentration – amount of solute dissolved in a solvent – Concentration decreases as the area/liquid increases 5

Starch Demo Start 6

Diffusion Particles in gases, liquids, and solids are in constant motion – Substances dissolved in water move constantly in a random motion called Brownian motion Diffusion – net movement of particles from an area of high concentration to an area of low concentration – No additional energy since particles are already in motion 7

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Diffusion Flow of particles eventually reaches equilibrium – Particles continue to flow but no further change in equilibrium or concentration on each side Larger particles move slower (large mass) – may be influenced by collisions with many nearby smaller particles Hotter particles move faster (more energy) – Rate of diffusion increases as temperature increases 9

Diffusion and Membrane Membrane has selective permeability – *some particles can pass through, others cannot Nonpolar molecules pass through more readily than polar molecules – Lipid bilayer (the fatty acid tails) is nonpolar and does not readily interact with polar molecules 10

What can pass through? Substances that can pass through the cell membrane: Nonpolar molecules (example: lipids) Small polar molecules such as water Substances that cannot pass through the cell membrane: Ions & charged molecules (example: salts dissolved in water) Large polar molecules (example: glucose) Macromolecules 11

Facilitated Diffusion Uses transport proteins to move ions and small molecules across membrane – Protein channels in the membrane 12

Carrier Proteins Carrier proteins within the membrane change shape as the molecule enters allowing it to enter or leave the cell 13

Osmosis Diffusion of water across a selectively permeable membrane When water can pass through a membrane and a solute (substance) cannot then osmosis occurs 14

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Osmosis Isotonic – concentration of solute is the same inside the cell and outside Water enters and leaves at same rate 16

Osmosis Hypotonic – concentration of solute is greater inside the cell, more water outside of cell – Cells gain water – Animal cells can burst due to osmotic pressure – Cell wall of plant cells prevents the cell from rupturing The osmotic pressure, turgor pressure, supports the cell A cell in which the contents are under pressure is turgid 17

Osmosis Hypertonic – concentration of solute is greater outside the 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 18

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What happens to a cell in isotonic, hypertonic, and hypotonic solutions? Agenda for Thursday Feb 17 th 1.Finish Starch Demo Questions 2.Gummy Bear Lab start 3.Finish Notes 4.Cells, Diffusion, Osmosis Review Sheet 20

Active Transport Def. – substances moving from lower to higher concentrations that require energy – Need energy because they move against the gradient Use carrier proteins – Some move particles in one direction – Some move particles in both directions 21

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 22

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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 allow other particles (sucrose/sugar) to move across membrane – Spend very little energy 24

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Transport of Large Particles Endocytosis – c ell surrounds a substance in the outside environment and brings it into the cell 26

Transport of Large Particles Exocytosis – secretion of materials at the plasma membrane – Expels waste, secrete substances (such as hormones) produced by cell 27

How does a large molecule get across the membrane? Agenda for Friday Feb 18 th 1.Finish Gummy Bear Lab 2.Quiz 3.Cell, Osmosis, Diffusion, Transport Review 28