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 16th 1.Diffusion/osmosis notes2.Start Lab3.Demo4.Look at Elodea

All late work is due Nov 29th 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

5

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

10

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

15

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 gradient17

18

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

20

Transport of Large ParticlesEndocytosis – cell surrounds a substance in the

outside environment and brings it into the cell

21

Transport of Large ParticlesExocytosis – 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 17th 1.Review2.Start lab3.Demo4.Practice stuff

Osmosis, diffusion, cell membrane, other QUIZ tomorrow

All Late work due Nov 29th 23