1. Passive Transport: Simple Diffusion & Osmosis
Cellular Transport
Passive Transport:
Simple Diffusion & Osmosis

2. There are two ways that materials move into & out of the cell membrane:
1. PASSIVE TRANSPORT– does not use energy
Examples: simple diffusion
osmosis
facilitated diffusion
2. ACTIVE TRANSPORT– requires energy (ATP)
Examples: endocytosis
exocytosis
pumps 2

3. Simple Diffusion Molecules are in CONSTANT, RANDOM motion
Molecules will naturally move from areas of HIGH concentration to LOW concentration; this DOES NOT require energy
Eventually, EQUILIBRIUM is reached and the concentration is approximately equal, but the molecules NEVER STOP MOVING
The difference between two areas of concentration is called a concentration GRADIENT 3

4. Simple Diffusion HIGH concentration EQUILIBRIUM LOW concentration

5. Example of simple diffusion:
If you spray air freshener in one corner of a room, it will eventually diffuse to all parts of the room, because of the random collision of air molecules.
(click on picture below for demo)
Question:
Will the scent spread quicker in warm air or cold air and WHY?
WARM air, because the air and perfume molecules are moving faster, meaning they collide more often. 5

7. Simple Diffusion, continued
In simple diffusion, molecules move “WITH” or “DOWN” the concentration gradient, meaning they travel from high to low; (no energy used)
the ability of a molecule to diffuse through the cell membrane depends on the SIZE and POLARITY of the molecule
Small molecules or molecules that are nonpolar can diffuse easily across the cell membrane, such as CO2 and O2
Large molecules (sugars, enzymes) or charged ions (Na+, K+) cannot easily diffuse across the membrane; they need “help” or “facilitation” to get through 7

8. Osmosis

9. What is Osmosis?
Osmosis is a type of passive transport; no energy is required
Osmosis is the movement of water across a membrane from high to low concentration

10. The Direction of Osmosis
Water will move in response to the SOLUTE concentration inside the cell and outside the cell.
Examples of solutes: salt, glucose, urea
Water molecules move to where the HIGHEST solute concentration is.

11. Types of Solutions
HYPERTONIC: there is a HIGHER solute concentration outside the cell
What is the direction of osmosis?
Water will move OUT of the cell
HYPOTONIC: there is a LOWER solute concentration outside the cell.
Water will move INTO the cell

12. Types of Solutions
ISOTONIC: the solute concentration outside the cell EQUALS the solute concentration inside the cell
Example of an isotonic solution:
BLOOD PLASMA (the clear part of our blood) has the same concentration of solutes as red and white blood cells

13. Isotonic Solution

14. Osmosis in Animal Cells
Animal cells contain cytoplasm, surrounded by a SEMIPERMABLE cell membrane.
nucleus

15. Osmosis Scenario #1
What would happen to a human skin cell if it were placed into concentrated salt water?

16. Water moves OUT of the cell by osmosis
What type of solution is salt water, relative to a normal human skin cell?
HYPERTONIC
In which direction will the water move?
Higher NaCl concentration
Lower NaCl concentration
Higher H20 concentration
Lower H20 concentration
Water moves OUT of the cell by osmosis

17. The cell loses water volume

18. The cell continues to lose water volume

19. The skin cell will SHRIVEL
End result
The skin cell will SHRIVEL

20. Osmosis Scenario #2
What would happen to a human skin cell if it were placed into distilled (pure) water?

21. Water moves INTO the cell by osmosis
What type of solution is distilled water, relative to a normal human skin cell?
HYPOTONIC
In what direction will the water move?
Lower NaCl concentration
Higher NaCl concentration
Lower H20 concentration
Higher H20 concentration
Water moves INTO the cell by osmosis

22. The cell gains volume and expands

23. The cell gains volume and expands

24. The cell gains volume and expands

25. The cell continues to expand…

26. End Result:
The skin cell will BURST/ LYSE because the cell membrane does not have the ability to resist the expansion pressure

27. Osmosis in Plant Cells
Plant cells are surrounded by a cell wall composed of CELLULOSE which…
Is freely permeable to water
Is inelastic
Able to resist cell expansion
Plant cells also have a large VACUOLE which…
Contains a solution of salt, sugars and other ions
Is bound by a selectively permeable membrane
Takes in or releases water by osmosis

28. Osmosis in Plant Cells
Cell wall

29. Osmosis in Plant Cells
Cell wall
Cell membrane

30. Osmosis in Plant Cells
Cell wall
Cell membrane
Vacuole

31. Water moves INTO the vacuole.
Osmosis Scenario #3
What would happen to a plant cell if it were placed into distilled water?
Lower Solute concentration
Higher Solute concentration
Lower H20 concentration
Higher H20 concentration
Water moves INTO the vacuole.

32. Osmosis Scenario #3 Distilled water = hypotonic solution
Lower Solute concentration
Higher Solute concentration
Lower H20 concentration
Higher H20 concentration
The vacuole swells, pushing the cytoplasm and cell membrane up against the cell wall

33. The cell wall resists expansion and the plant cell becomes TURGID.
Osmosis Scenario #3
End Result:
The cell wall resists expansion and the plant cell becomes TURGID.

34. Water moves OUT OF the vacuole
Osmosis Scenario #4
What would happen if a plant cell were placed into a solution of concentrated sugar water?
Higher Sugar concentration
Lower Sugar concentration
Higher H20 concentration
Lower H20 concentration
Water moves OUT OF the vacuole

35. The vacuole shrinks, pulling the cytoplasm away from the cell wall
Osmosis Scenario #4
Sugar water = hypertonic solution
Higher Sugar concentration
Lower Sugar concentration
Higher H20 concentration
Lower H20 concentration
The vacuole shrinks, pulling the cytoplasm away from the cell wall

36. Osmosis Scenario #4 End Result:
The cell membrane “peels” away from the cell wall
The plant would appear WILTED and limp and after a while, could die from dehydration

37. Discussion Question
Why does your skin become “pruney” after taking a bath or swimming in a pool?
A bath is a HYPOTONIC solution: there are more solutes inside your cells than in the water. When osmosis occurs, water will move INTO your skin cells, causing them to swell and appear wrinkled or “pruney”