Describe the cell membrane and its components.

Agenda for Wednesday Feb 16th 1.Finish work from yesterday2.Diffusion and Osmosis

1. Starch Demo and Questions

1

2

3

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

increases5

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

8

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

15

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

19

What happens to a cell in isotonic, hypertonic, and hypotonic solutions?

Agenda for Thursday Feb 17th 1.Finish Starch Demo Questions2.Gummy Bear Lab start3.Finish Notes4.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 gradient22

23

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

25

Transport of Large ParticlesEndocytosis – cell surrounds a substance in the

outside environment and brings it into the cell

26

Transport of Large ParticlesExocytosis – 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 18th 1.Finish Gummy Bear Lab2.Quiz3.Cell, Osmosis, Diffusion, Transport Review

28