1. Passive Transport

2. The Cell Membrane
There are 2 important parts of the cell membrane regarding transport:
Phospholipids
Proteins
Cells need nutrients from the exterior environment. As cells process these nutrients, wastes build up in the cell = must eliminate them.
Ext. env. 1. 2.
Inside cell
CMs are selectively permeable – only certain substances can go in and out of them!

3. The Living Cell Membrane
CM is composed of 2 layers of phospholipids
each phospholipid molecule has a head and 2 tails
the head is hydrophilic (attracts water) and soluble in water
the tails are hydrophobic (repels water) and insoluble in water

4. The Living Cell Membrane
A variety of protein molecules are embedded within the bilayer
Many of these proteins carry special sugar molecules (glycoproteins)
help distinguish type A vs. type B blood cells
The protein molecules serve different functions:
Gatekeepers - opening and closing paths through the cell membrane
Receptor sites for hormones - chemical messengers that allow cells to communicate with one another
Transport - pick up materials and move them into and out of the cells

6. Types of Passive Transport
Transport of materials across CM without using energy.
There are 3 types:
Simple Diffusion
Osmosis
Facilitated Diffusion

7. 1. Simple Diffusion
Movement of molecules from an area of high concentration to an area of low concentration
Goal is to achieve equilibrium
Affected by concentration, temperature and pressure
*** HIGH  LOW ***

8. Examples of Simple Diffusion
H2O, CO2, O2 molecules with cells (involved in life processes)
Air freshener cones
Perfume sprays

9. 2. Osmosis
Diffusion of water molecules across a selectively permeable membrane
Cells are ideally bathed in isotonic solutions (where conc. inside cell equals conc. outside cell)
H2O molecules move from a side with low conc. to a side with high conc. across a selectively permeable membrane to obtain equilibrium
SP membrane allows water to go through, but not other molecules

10. Osmosis happens when there is a difference in solute conc.
Result:
Equal conc. of sugar solution on BOTH sides
SP membrane keeps sugar molecules from moving to other side! (impermeable to them)

11. Types of Solutions
Recall: A solution is a uniform mixture made up of a solvent (the bigger part) and a solute (the smaller part)
3 Types:
Isotonic – conc. of solute inside cell EQUALS conc. of solute outside the cell
Hypertonic – conc. of solute inside cell is HIGHER than conc. of solute outside the cell
Hypotonic – conc. of solute inside cell is LOWER than conc. of solute outside cell
Now… if you have red blood cells in a beaker full of water and you add salt to the beaker… what would be the hypothetical situation for each of these solutions?

12. Isotonic – conc. of salt inside cell EQUALS conc. of salt outside cell
Isotonic – conc. of salt inside cell EQUALS conc. of salt outside cell. Water moves in and out at equal rates. Nothing happens to cell size.
Hypertonic – conc. of salt inside cell LOWER than conc. Of salt outside cell. Water moves OUT to adjust conc. = cell SHRINKS
Hypotonic – conc. of salt inside cell GREATER than conc. Of salt outside cell. Water moves IN to adjust conc. = cell SWELLS & may burst 1. 2. 3.

15. 3. Facilitated Diffusion
Protein carrier molecules speed up movement of molecules moving already
The carrier proteins must be specialized to aid the diffusion of these molecules as it has a specific fit.

16. high concentration outside cell lower concentration inside cell
molecule bounces into a specific carrier protein
carrier protein binds molecule
carrier changes shape & flips over, bringing molecule into cell
carrier protein resumes its shape 16

17. Summary of Passive Transport higher concentration outside of the cell1 2 3
1. directly through phospholipid bilayer
ex • O2
• CO2 • H2O
• diffusion
and osmosis
2. protein channels
charged ions & water
ex. Na+, Ca2+, K+, Cl-
diffusion and osmosis
3.carrier protein
facilitated diffusion
larger molecules
ex. glucose, amino acids 17